Design and feasibility study for the application of an inflatable rubber structure in a navigation lock.

Transcription

1 Delft University of Technology Master of Science Thesis report Design and feasibility study for the application of an inflatable rubber structure in a navigation lock. Steffen Woudstra Steffen Woudstra I

2 II Master thesis Application of an IRS in a navigation lock

3 Design and feasibility study for the application of an inflatable rubber structure in a navigation lock. Author: S.D. Woudstra Assessment Committee: Prof. dr. ir. S.N. Jonkman Ir. W.F. Molenaar Ir. S. Pasterkamp Ing. D.H.M. Adriaansens Document: Master of Science Thesis report Date: Steffen Woudstra III

4 PREFACE This report consist of the results of the Master of Science Thesis Design and feasibility study for the application of an inflatable rubber structure in a navigation lock. The application of an inflatable rubber structure in a navigation lock is an innovative water saving concept. The study has been conducted for the specialisation Hydraulic Structures and Flood Risk, which is part of the master studies Hydraulic Engineering. The idea of the application of an inflatable rubber structure in a navigation lock was founded by engineering consultancy firm Grontmij N.V. In Dutch the concept is called Balgsluis. The study has been conducted in the Grontmij office in De Bilt and was guided and supervised by Delft University of Technology and Grontmij. I especially would like to thank my graduation committee consisting of Prof. dr. ir. S.N. Jonkman, Ir. W.F. Molenaar, Ing. D.H.M. Adriaansens and Ir. S. Pasterkamp for their support and advice throughout the master thesis. Furthermore, I would like to thank my colleagues at the office of Grontmij for sharing their experience in the design of hydraulic structures. Utrecht, November 2014 Steffen Woudstra IV Master thesis Application of an IRS in a navigation lock

5 ABSTRACT Navigation locks separate a waterway in two sections with a different water level. During locking levelling is executed under free flow. The net flow from the upper section into the lower section of the waterway is considered as a water loss. In case of water scarcity, a water loss can be undesirable. For such situations, water saving measures are applied in navigation locks. An innovative water saving concept is an IRS Lock (in Dutch: Balgsluis). IRS stands for inflatable rubber structure. The IRS Lock concept consists of an air filled IRS applied in a lock chamber. In this way part of the water in the lock chamber is substituted by air, and in that part the water loss is substituted by an air loss. Before the start of this thesis it was not clear whether or not the IRS Lock concept is a feasible water saving solution. Theoretical background Inflatable rubber structures are formed by a rubber sheet connected to a foundation. The structure is filled with a filler medium. The rubber sheet is so flexible that it is considered to have no bending stiffness. The shape of the IRS results from the loads acting on the sheet. Therefore a different load condition results in a different equilibrium shape of the IRS. Similarly, for dynamical loads the shape of the IRS is variable. During the use of an IRS, four phases are distinguished; the inflation phase, the inflated phase, the deflation phase and the deflated phase. In each phase, the internal pressure is different. During the inflation and deflation phases, the internal pressure varies over time. This results in a different shape and stiffness at each phase. Currently, IRSs are applied in hydraulic environments as storm surge barriers, dams and weirs. These structures have in common that the main load on the IRS caused by a head difference acting perpendicular to the longitudinal axis of the IRS. In case of the IRS Lock, no head difference is present inside the lock chamber and the IRS is completely submerged. The hydrostatic load is the main external load. Smaller, locally acting, loads occur by flows from lock operations and vessel movements. The different phases of use, shapes and the new application area make the design of the IRS Lock a complex process. Design IRS Lock In this thesis, a first design of the IRS Lock has been developed. The Eastern Lock, located in the Terneuzen Lock complex, was used as an environment for the design of the IRS Lock. The lock separates the Gent-Terneuzen Canal and Western Scheldt. Because of the available lift and the size of the lock chamber (CEMT class 6b), an average water loss of m 3 per lock cycle occurs. Several alternative designs have been developed for the IRS Lock. With help of a Multi Criteria Analysis the best alternative was selected. The sheet connected to the walls design was found to meet the criteria best and this alternative has been elaborated. A cross section of the selected alternative is given in Figure 1. The connection of the sheet to the lock chamber walls leads to a design in which the volume inside the IRS is relatively large compared to the other alternatives. Figure 1 Impression of the cross section of the design 'sheet connected to the walls'. Steffen Woudstra V

6 In navigation locks a minimum keel clearance is required between the vessel and the lock chamber bottom. The IRS is located above the bottom of the lock chamber and therefore impacts the available keel clearance. The tidal movement in the Western Scheldt varies the water level in the lock chamber, and therefore also the available depth and keel clearance. The first design of the IRS is optimized in such a way that the design results in a large water saving while maintaining the minimum required keel clearance. The designed IRS has a crest height of 2,5 meter and still allows the draught of the design vessel of 4,3 meter. During all phases of use, the designed sheet has a relatively small vertical reach. Therefore the design minimally affects the available keel clearance. Equilibrium equations were used to determine the shape of the IRS. After the shape of the midsection of the submerged IRS was found, a 3D layout of the total IRS has been designed. In total three IRSs are applied in the length of the Eastern Lock. Additionally, several elements of the IRS Lock have been elaborated. Among others the strength of the rubber sheet has been verified and an impression of the sheet connections and the bottom recess has been made. Furthermore, the required pump capacity for inflating the IRS has been calculated. Functional performance of the design The functional performance of the first design of the IRS Lock has been assessed. First, the water volume that will be saved has been calculated. Per Lock cycle the designed IRSs will save 9056 m 3 of water. Because of the tidal fluctuations in the water level of the Western Scheldt, and the limitations in available depth and keel clearance, the IRS can only be used for 6 of the 18 lock cycles per tidal period. The total amount of water that is saved per tidal period is calculated to be m 3. This amounts results in a saving of on average 25% of the total water loss. If the Eastern Lock would be located in an environment with a constant lift of 2,5 meter, the water saving is expected to be 52%. Besides the saved water volume, the energy consumption and the total life cycle cost (LCC) of the IRS Lock have been determined. The LCC are estimated to be 124 million (Net Present Value, 2% discount rate) for a lifetime of 20 years. The largest cost component is the periodic renewal of the sheet, which represents 55% of the total LCC. An alternative for the IRS Lock is a pumping station that pumps the lost volume of water back into the upper section of the waterway. It has been found that in all possible situations the IRS Lock will use more energy per unit of saved volume than a pumping station. Also the LCC are higher. This makes a pumping station a more economical solution. As part of a RAMS-analysis, a Failure Mode Effect Analysis (FMEA) has been performed. The FMEA gives insight in the failure mechanisms of the IRS Lock and the quality of the system. The failure mechanisms with the largest risk are related to maintaining the required pressure inside the IRS. Measures have been taken to keep the risk of failure at an acceptable level. Conclusion From the functional performance of the first design it follows that the designed IRS Lock is technically feasible. Economically the IRS Lock concept is less attractive. The application of the IRS leads to a longer duration of the lock cycles, a smaller availability of the lock chamber and larger life cycle costs. VI Master thesis Application of an IRS in a navigation lock

7 Content Preface... IV Abstract... V Symbols and units... XI Abbreviations... XIV 1 Introduction The IRS Lock concept in short Structure of the report Introduction in locks and water losses Functions Types of navigation locks Layout and dimensions Water loss in locks Water saving concepts Inflatable rubber structures Introduction to IRSs State of the art: Ramspol barrier Equilibrium in the rubber sheet Shape of the sheet Behaviour during inflation and deflation Sheet material Filler medium Stiffness of IRSs Bottom recess Hydraulic loads in navigation locks Loads by lock operations External loads Loads by moving vessels Incidental loads Problem and objective Problem and objective Approach Analysis of the IRS Lock concept Background Steffen Woudstra VII

8 6.2 The principle of the IRS Lock System Functional requirements Case for the design of the IRS Lock Optimal case selection Description selected case: Eastern Lock Boundary conditions Development of alternatives Development of alternatives Multi Criteria Analysis alternatives Optimal crest height and shape of the midsection of the IRS Water levels for which IRS is used Crest height of the IRS Shape and equilibrium midsection Hydraulic loads in the IRS Lock Loads per phase of use of the IRS Size of the loads Loads taken into account in the design of the IRS Lock Design layout total IRS and sheet Layout midsection Layout ends Layout of transition section Overview total layout IRSs and sheet Integration of the IRS in the lock chamber Amount and length of the IRSs Availability minimum keel clearance during all phases of use Overview final design IRS Lock Design elements Sheet Connections Bottom recess Pumping equipment Functional performance Lock cycle time IRS Lock VIII Master thesis Application of an IRS in a navigation lock

9 14.2 Effectiveness for water saving RAMS-analysis Energy consumption Life Cycle Cost Conclusions and recommendations Conclusions Recommendations References List of figures List of tables Steffen Woudstra IX

10 Content appendices Appendix 1 Field with unknowns for further research Appendix 2 Case selection process Appendix 3 Shape and equilibrium IRS in Large Sea Lock Appendix 4 Assessment alternatives Multi Criteria Analysis Appendix 5 Calculations for the height of the optimal IRS Appendix 6 Selection filler medium Appendix 7 Calculation hydraulic loads acting on the IRS Appendix 8 Alternatives layout ends of the IRS Appendix 9 Vertical reach of the rubber sheet Appendix 10 Improvements of the sheet Appendix 11 Estimation life cycle cost Appendix 12 RAMS-analysis Appendix 13 Failure Mode Effect Analysis List of figures appendices List of tables appendices X Master thesis Application of an IRS in a navigation lock

11 SYMBOLS AND UNITS Main report a Half the major axis of the ellipse [m]. A Horizontal cross sectional area of the lock chamber [m 2 ] A tide The amplitude of the average astronomical tide: 2,09 [m]. b Half the minor axis of the ellipse [m]. B Base width of IRS, distance between the two parallel clamp lines [m]. d keelclearance Minimum required keel clearance [m] d minkeel Minimum required depth for keel clearance [m] d minkeel,def Minimum required depth for keel clearance during deflated phase [m] d minkeel,inf Minimum required depth for keel clearance during inflated phase [m] d min,deflated Minimum available depth during the deflated phase [m] d min,deflation Minimum available depth at start deflation phase [m] d min,inflated Minimum available depth during the inflated phase [m] d min,inflation Minimum available depth at start inflation phase [m] d vessel Draught design vessel [m] ds The length of a rubber element in unloaded state (Parbery) [m] dt Membrane force at the start of a rubber element (Parbery) [kn] dα Angle of the element, previously called dφ (Dorreman) [rad] dφ Angle at the start of a rubber element (Parbery) [rad] E p Potential energy [kj] F f the friction force [kn] F 1, F 2 Foci of ellipse [-] g Gravitational acceleration [m/s 2 ] h Water depth [m] h max,sheet The largest height to which the sheet can reach [m] H Resulting horizontal load per meter from head difference [kn/m] H Internal pressure, previously called p (Dorreman) [m water column] HW HW = external water level measured from the level of the connections [m] H WS The water level in the Western Scheldt only by the tide [m NAP] L Width of the rubber sheet [m] m The mass of an object [kg] n The number of water saving basins [-] n The amount of gas [mol] N force normal to surface bottom recess [kn] p Working pressure inside the IRS, positive when outwards directed [kpa] P Point on ellipse [-] p internal The pressure inside the IRS acting on the sheet [bar] p external The pressure outside the IRS acting on the sheet [bar] P f The probability of failure [-] p hydrostatic Hydrostatic water pressure [kpa] P min,lift Period during which a at least a defined lift is available [hours] P 1 The original pressure in the gas [bar] P 2 The second pressure in the gas [bar] R Resistance, representing the strength of an element R Gas constant [J/(molK] R d Design value of the strength R rep Representative value for the strength RH Horizontal support reaction force [kn] Steffen Woudstra XI

12 RV Vertical support reaction force [kn] r 1, r 2 Distances from point P to Foci [-] R 1, R 2 Radii of curvature in respectively meridional and hoop direction [rad] S The coordinate in warp direction of the rubber sheet (Parbery) [-] S Load acting on an element SCF Factor giving ratio stress concentrations relative to stress at midsection due to static membrane force[-] S d Design value of the load S rep Representative value for the load t The time which is 0 at the start of the tidal cycle [hours]. T Membrane force [kn/m] T The absolute temperature [K] T gates Time needed for opening or closing the gates [min] T levelling1 Base time needed for levelling [min] T levelling2 Additional time for levelling per meter lift [min/m] T lockcycle The total time needed for a lock cycle in both directions [min] T tide The period of the tide: 24,84 [hours] T vessel Time needed for vessels moving in or out of the lock chamber [min] T θ The membrane force in the meridional direction [kn/m] T τ Friction force per meter width of the IRS [kn/m] T φ The membrane forces in the hoop direction [kn/m] T 1 The temperature in the original gas [ K] T 2 The temperature in the compressed gas [ K] V Volume [m 3 ] V end Internal volume of the end of the IRS [m 3 ] V IRS Internal volume IRS [m 3 ] V levelling Volume needed for levelling [m 3 ] V loss Water loss per lock cycle [m 3 ] V midsection Internal volume of the midsection of the IRS [m 3 ] V transition Internal volume of the transition section of the IRS [m 3 ] V water Volume of water needed for levelling [m 3 ] V 1 The original volume of the gas [m 3 ] V 2 The second volume of the gas [m 3 ] w Weight of a rubber element (Parbery) [kn/m] W down Amount of water displaced by vessels sailing downstream [m 3 ] W up Amount of water displaced by vessels sailing upstream [m 3 ] W 1-2 Work done for compressing a gas [kj] x Coordinate in x-direction [m] x 0 Coordinate origin ellipse [m] y Coordinate in y-direction [m] y i The height of an element above the sheet connections [m] y 0 Coordinate origin ellipse [m] z The lift over a lock [m] Z Limit state function [-] z tide The mean water level of the average astronomical tide: +0,2 [m NAP]. γ dyn Factor giving ratio dynamical membrane force relative to static membrane force at midsection [-] γ end Factor giving ratio membrane force at end relative to membrane force midsection [-] γ longitudinal Factor giving ratio membrane force in longitudinal direction to membrane force at midsection [-] γ m Material factor [-] γ R Safety factor for the strength [-] XII Master thesis Application of an IRS in a navigation lock

13 γ S Safety factor for load [-] Δz IRS Change in the water level by the inflation or deflation of the IRS [m] Δz levelling Total change in the water level by levelling operations, which is equal to the lift [m] Δz water Change in the water level by adding or removing water from the lock chamber [m] κ Curvature in a rubber element (Parbery) [m -1 ] μ f friction coefficient [-] ρ Mass density of water [kg/m 3 ] φ 1, φ 2 Angle between the rubber sheet and lock chamber floor at the support [radians] Appendices A lc Wet cross section of the lock chamber [m 2 ] A v Wet cross section of the vessel [m 2 ] b lc The width of the lock chamber [m] b n Total width of the jet flow just behind the opening for levelling [m] b v Width of the vessel [m] c k Propagation speed of the translation wave, (g*d) 0,5 [m/s] d lc The depth of the lock chamber [m] d n Total height of the jet flow just behind the opening for levelling [m] d p The vertical distance from the centre of flow to the bottom [m] d v Draught of the vessel [m] D 0 Effective diameter of the propeller [m] e n Height of the centre of the jet flow above the lock chamber floor [m] g Gravitational acceleration [m/s 2 ] h lc Water level in the lock chamber [m NAP] h opening Height above the sill of the opening for levelling [m] h sill Height of the sill above the lock chamber floor [m] i Slope of the energy line in a uniform flow [-] l k Length of the lock chamber [m] L Length of the slope [m] n 1 The initial wave height [m] n 2 The water level depreciation [m] P d Engine power that is used by the propeller [kw] Q f Discharge by flushing [m 3 ] Q n Maximum discharge through the openings for levelling [m 3 /s] R Hydraulic radius of the waterway [m] T k Eigen period of the translation wave [s] T τ Friction force per meter width of the IRS [kn/m] u Velocity averaged over the height and time [m/s] u bp The maximum flow velocity at the bottom [m/s] u dp The maximum velocity occurring at location x dp [m/s] u f Current by flushing [m/s] u n Velocity just behind the opening by levelling operations [m/s] u p Velocity just behind the propeller [m/s] u r Return current [m/s] u xn Velocity at a distance x from the origin of the jet flow [m/s] v bp2 The maximum flow velocity at the bottom at a horizontal distance y bp2. v l Limit speed [m/s] v max Maximum speed of vessel (equal to the limit speed v l ) [m/s] v p Velocity of the flow just in front of the thrusters [m/s] v si Sailing speed, the limit speeds are governing [m/s] x Horizontal distance from the origin of the jet flow [m] Steffen Woudstra XIII

14 x bn Horizontal distance from the origin of the jet to the location at the bottom [m] x dp Horizontal distance from the propeller to the maximum velocity at the bottom or top of the IRS [m] y bp2 The horizontal distance to the intersection of a line from the centre of the flow with a slope of 1:10 with the bottom. z b Level of the lock chamber bottom [m NAP] α Angle of the centreline of the jet flow with the horizontal [degrees] β Coefficient return current [-] γ Slope of the water surface caused by a translation wave [-] Δh Vertical difference in the energy line along the slope [m] Δh Amplitude of the translation wave [m] ζ A factor for the energy loss because of the canal system of bow thrusters with a sideways outflow. λ 1 Coefficient water level increase primary wave [-] λ 2 Coefficient water level decrease primary wave [-] τ b Bottom shear stress [N/mm 2 ] ABBREVIATIONS CEMT GTC IRS IRSs LAT LCC LLWS NPV RAMS SCF UHMWPE WS WSB Conférence Européenne des Ministres de Transport Gent-Terneuzen Canal Inflatable rubber structure Inflatable rubber structures Lower Astronomical Tide Life Cycle Cost Low Low Water Spring Net Present Value Reliability, Availability, Maintainability, Safety Stress Concentration Factor Ultra-High-Molecular-Weight Polyethylene Western Scheldt Water saving basin XIV Master thesis Application of an IRS in a navigation lock

15 1 INTRODUCTION Engineering consultancy firm Grontmij N.V. has found an innovative concept for reducing the water loss by levelling operations in navigation locks. The concept consists of an inflatable rubber structure (IRS) applied in a navigation lock. In English the concept is called IRS Lock. In this chapter a short introduction on the concept is given together with the structure of this report. 1.1 THE IRS LOCK CONCEPT IN SHORT Because of increasing navigation intensities the capacity of lock complexes is enlarged by constructing more and larger lock chambers. In general in The Netherlands the available space in lock complexes is already limited and the construction of extra lock chambers leads to scarcity of space. With the increasing intensities of navigation also the intensity of locking increases and thus the water loss due to levelling operations. A water loss is a problem in cases where water scarcity exists. In practice for such cases several water saving solutions are applied. The solutions have in common that they require a lot of space, which is already scarce in lock complexes. Pumping stations require the least amount of space, but pumping of water costs a lot of energy. Engineering consultancy firm Grontmij N.V. initialized the IRS Lock concept as a solution for the above problems. In the IRS Lock concept a large volume of the water in the locking chamber is substituted for an air filled IRS, see Figure 2. The IRS is air and water tight. The IRS will be inflated and deflated as part of the levelling operations of the navigation lock. In this way, part of the water loss will is substituted by an air loss. Besides the advantage in quantitative water management, the rubber structure can also have an advantage for qualitative water management. In the case of a navigation lock that separate different water qualities, the intrusion of low quality water will be reduced by the use of an IRS Lock. The IRS Lock concept needs further technical elaboration and a study of the economic and technical feasibility. Figure 2 Overview of the IRS Lock concept. The inflatable rubber structure is shown in yellow. Steffen Woudstra

16 Design IRS Lock Theoretical background System and boundaries 1.2 STRUCTURE OF THE REPORT This report consists of three main parts. These parts are grouped in the schedule below. The numbered boxes are representing the individual chapters. The first part of the report covers the theoretical background of the IRS Lock. Thereafter the system and boundaries are described. After that a design has been developed for the IRS Lock. The design has been evaluated for its functional performance. With help of the results of the evaluation the design is further improved in a cyclic manner. 1 Introduction 2 Introduction in locks and water losses 3 Inflatable rubber structures 6 Analysis IRS Lock concept 4 Hydraulic loads in a navigation lock 7 Case for the design of the IRS Lock 8 Development of alternatives 5 Problem and objective 9 Crest height and shape of the midsection 10 Hydraulic loads in the IRS Lock 11 Design layout total IRS and sheet 12 Integration of the IRS in the lock chamber 13 Design elements 14 Functional performance 15 Conclusions and recommendations 2 Master thesis Application of an IRS in a navigation lock

17 2 INTRODUCTION IN LOCKS AND WATER LOSSES This chapter describes in short some general aspects of navigation lock. After the general aspects the water loss in navigation locks is explained. In the end existing solutions for reducing the water loss in navigation locks are presented. 2.1 FUNCTIONS One of the functions of a navigation lock is maintaining a water level difference. In other words, the navigation lock is retaining the higher water level. The water head difference between both sections of the waterway is called the lift of the lock. Another function of a navigation lock is offering ships the possibility for passing the lock in horizontal and vertical direction. Besides the water retention and ship passage function, a navigation lock can have a water quality management function. This function depends on the surrounding of the navigation lock. For example in the case of a navigation lock in a coastal area, the navigation lock separates salt and fresh water. Summarized the main functions of a navigation lock are: Water retention Ship passage Water quality management In case the lock is part of a primary sea defence, the lock also has the function of storm surge barrier. 2.2 TYPES OF NAVIGATION LOCKS Different types of structures can perform the functions of a lock. The most common structure used for navigation locks is the so called traditional lock. The traditional lock consisting of among others a (generally) rectangular lock chamber located in the centre axis of the waterway, lock doors and a filling and emptying system. Additional measures and structures providing a save and clear approaching route for vessels are also part of the lock. A typical traditional lock is shown in Figure 3. Figure 3 Traditional navigation lock in Terneuzen ([W1] Other types of locks are the lift lock, inclined plane, the rotating wheel and Pente d eau. The lift lock and rotating wheel are moving a closed chamber in vertical direction. The lock chamber is accommodating a vessel(s) and the surrounding water. In the inclined plane a closed lock chamber is moved over a slope in horizontal and vertical direction. The Pente d eau is making use of a sloping channel where a vessel and the surrounding water is being moved using a more or less watertight door, pushing the water up or down the sloping channel. Steffen Woudstra

18 2.3 LAYOUT AND DIMENSIONS The design of the layout and dimensions of navigation locks is based on the possibility for safe and quick navigation through the lock and also on economical considerations Layout The most obvious part of traditional navigation locks are commonly the lock chamber and the lock approach route. In the approach route measures are taken to provide a save and clear guidance from the waterway into the lock. Waiting berths, number(1) in Figure 4, are situated in front of the lock to provide a safe mooring place for vessels that have to wait before entering the lock. A guiding wall (2) is used to guide vessels and protect the lock structure from vessels. The main parts of the lock structure are the lock gates (3), the lock heads (4) and the lock chamber (5). During the locking cycle a filling and emptying system (6) is used to alter or lower the water level in the lock chamber. The difference in water head over the lock will result in a groundwater flow underneath and along the lock structure. This flow, called seepage, may result in piping (erosion of the soil). Therefore cut-off walls and/or cut of screens (7) are applied that prevent. Additionally, a bottom protection (8) at both ends of the lock is applied if needed for preventing bottom erosion by flows from shipping and lock operations. Figure 4 Lay-out of a navigation lock ([L1] W.F. Molenaar and others). The layout described before is the typical layout for inland navigation locks. For navigation locks in coastal areas additional measures can be needed. Breakwaters are usually applied to protect incoming and outgoing vessels from waves and alongshore currents. 4 Master thesis Application of an IRS in a navigation lock

19 2.3.2 Dimensions The horizontal and vertical dimensions of locks are described by standards and codes supplied by authorities. In The Netherlands, Rijkswaterstaat (the executive body of the Dutch ministry of Transport, Public Works and Water Management) supplies standards called Waterway Guidelines. The standards are describing minimum horizontal dimensions of navigation locks. The size of cargocarrying commercial vessels are governing for the dimensions of the main waterways and accompanying structures. The design process of an inland waterway and related structures starts with the definition of the desired CEMT class. The CEMT classes are defined by the Conférence Européenne des Ministres de Transport and called CEMT classes. After the definition of the CEMT class the design process of a waterway continues with the definition of the so-called reference vessel. The reference vessels is the largest vessel that can smoothly and safely navigate in the waterway. For a waterway used by sea vessels a similar approach is used. Because the water consumption and construction cost of a navigation lock are increasing with horizontal dimensions of the lock, the horizontal dimensions are kept as small as possible. The final dimensions are chosen based on the risk of damage and the requirement that vessels can enter and exit the lock smoothly and within a short time. The depth of a lock is determined by the vessels maximum draught and squat, a hydraulic margin and a safety margin as well as a margin for wave phenomena which can cause water level fluctuations. In Figure 5 an overview of these vertical components is given. The squat is the phenomenon by which a vessel moving quickly through shallow water creates an area of low pressure that causes the ship to be closer to the bottom of the waterway. More about the wave phenomena around a vessel sailing in navigation locks is given in chapter 4. Figure 5 Overview components of the keel clearance ([L2] Rijkswaterstaat). Steffen Woudstra

20 2.4 WATER LOSS IN LOCKS The IRS Lock idea was founded for Eefde (The Netherlands) where during dry periods water lost by navigation locks is pumped back from the lower to the higher section of the Twentekanaal. In a traditional navigation lock the water loss per locking cycle can be schematised as in Figure 6. Figure 6 Water loss during locking cycle ([L1] W.F. Molenaar and others). The amount of water lost per locking cycle in a traditional navigation lock is: Where: A = the horizontal cross sectional area of the lock chamber [m 2 ] z = the lift over the lock chamber [m] W up = amount of water displaced by vessels sailing upstream [m 3 ] W down = amount of water displaced by vessels sailing downstream [m 3 ] As can be seen with Figure 6 and the different lock types described before, the amount of water lost per cycle will be larger in a traditional navigation lock than in the other navigation lock types. The amount of water lost per cycle in the locks with a moving chamber is in principle only W up W down. If there is a need for levelling the water in the lock chamber with the adjacent waterway, an additional volume A*z could be lost. In practice usually an imbalance in the direction of shipping traffic occurs, and so W up and W down will be unequal. The IRS Lock idea is created in order to reduce the part of the water loss A*z. The loss A*z happens due to the water head difference over the navigation lock (lift). In case there is no lift z is zero and so is A*z. The part of this area filled by the rubber structure is representing the reduction of the water loss. When the area A*z is small (small lift or small horizontal dimensions of the lock chamber), water saving measures generally are not needed. To get an idea of the volume lost per cycle an example from practice are given for the Eefde navigation lock. For Eefde the area A is equal to 140 meter by 12 meter. On average the lift of the lock is more or less 6 meter. This result in a water loss per locking cycle of 140*12*6 = m 3. Obviously, larger lock dimensions are a larger lift will quickly increase the lost volume of water. 6 Master thesis Application of an IRS in a navigation lock

21 2.5 WATER SAVING CONCEPTS In practice the water in locks is reduced with help of several water saving concepts, reducing or compensating for the part of the water loss indicated before as A*z: Pumping Intermediate gates Twin locks (parallel) Water Saving Basins (WSBs) Lock ladder Pumping Pumping in principle is not a saving concept but a way to compensate for the water loss. When filling the lock chamber, a water volume A*z flows from the higher section of the waterway into the lock chamber. The lock chamber is emptied by pumping the volume A*z from the lock chamber into the higher section of the waterway. With the above levelling procedure there is no water loss Intermediate gates An intermediate gate can be used if the vessels in a navigation lock only occupy part of the inner length L of the lock chamber. By using the intermediate gates, the total length L between the lock gates becomes smaller, and so is the volume of the water loss. The reduction in the water loss depends on the location of the intermediate gates Lock ladder The lock ladder is a series of locks connected to each other. When leaving a lock chamber, the next lock chamber is entered. In principle the lock ladder is the same as a lock with water saving basins: a portion of the water flowing out of the lock chamber during emptying, is used as part of the filling water for the next lock chamber Twin locks Two lock chambers are placed parallel to each other and joined by one or more culverts with valves withstanding reverse water heads. A lock chamber is filled with water from the other lock chamber. That means filling of one lock chamber will take place at the same time as emptying of the other lock chamber. The maximum saving possible is 0,5*A*z, achieved for the same amount of traffic in both directions (W up = W down ). For vessels going in one direction the situation is comparable to one lock chamber with one Water Saving Basin. In such a situation the maximum saving possible is 0,3*A*z. A top view of the lay-out of a twin lock is given in Figure 7. The culvert between the lock chambers is indicated with a 1, the valve withstanding a reverse water head is indicated with a 2. Figure 7 Top view of a twin lock ([L3] PIANC). Steffen Woudstra

22 2.5.5 Water Saving Basins The principle of WSBs is that a portion of the water flowing out of the lock chamber during emptying, is used as part of the filling water for the next lock cycle. Neglecting energy losses, for basins with similar horizontal dimensions as the lock area (a), the ratio of the water saving compared to the loss without saving basins becomes: Where: n = the number of saving basins. A typical emptying and filling operation with two water saving basins (A and B) is shown in Figure 8. obviously the ratio of the water saving will be 0,5 in case of two saving basins. Figure 8 Method water saving basins ([L4] Panama Canal Authority). A recently constructed navigation lock with water saving basins is the Hohenwarthe navigation lock. The lock is located near Magdeburg, Germany. The lock complex consist of two parallel lock chambers with six parallel water saving basins each. An overview of the Hohenwarthe navigation lock is given in Figure 9. The length of the lock chambers is 200 meter, the width of each lock chamber is 12,5 meter and the lift of the lock is between 18,55 and 19,05 meter. Hence, on average the theoretical water loss per lock cycle per lock chamber for equal traffic in both directions is 200*12,5*18,8 = m 3. The use of the WSBs are resulting in a 60% reduction of the water loss for both lock chambers. This equals a water volume of m 3 per lock cycle per lock chamber. Figure 9 Overview Hohenwarthe navigation lock ([W2] 8 Master thesis Application of an IRS in a navigation lock

23 3 INFLATABLE RUBBER STRUCTURES In this chapter the theoretical background of IRSs applied in hydraulic environments is given. At first the structure and equilibrium of forces are explained. Later the material properties, and information about the stiffness, inflation and deflation and the bottom recess of the IRS are given. 3.1 INTRODUCTION TO IRSS IRSs applied in hydraulic environments are well known as inflatable weirs and inflatable dams. In 1955 the inflatable dam concept has been found by Mesnager (France). In 1957 the first inflatable dam has been constructed in the Los Angeles River (USA). Inflatable weirs are often used to create temporary closure dams or water basins and are applied in smaller rivers and channels. An inflatable weir in practice is shown in Figure 10. Figure 10 Inflatable weir ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics). One of the most controversial inflatable dams so far constructed is the Ramspol barrier (The Netherlands). The Ramspol barrier consists of three separate rubber dams. The dams each have a crest length of more or less 78 meter and a crest height of 8 meter above the foundation. An impression the Ramspol barrier is shown in Figure 11. Figure 11 The Ramspol barrier during the construction, deflated on the left and inflated on the right ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics). An IRS consists of at least a foundation, the rubber sheet, a filling and emptying system and, if needed, abutments. The filling and emptying system normally includes pumps and conduits through the foundation or abutments. The pumps are usually filling the rubber structure with water or air or a combination of both air and water. The rubber sheet is connected to the foundation with help of clamps, which are forming a water and air tight connection between the sheet and the foundation. Steffen Woudstra

24 Both the longitudinal edges of the rubber sheet can be clamped together in one line, or in two separate lines. The result is a so-called one-sided clamped rubber structure or a two-sided clamped rubber structure. The clamps together are forming the clamp line(s).the Ramspol barrier obviously is a two-sided clamped IRS. In Figure 12 an impression of a one-sided clamped IRS is given. Also the clamps used to connect the sheet to the foundation is clearly visible in Figure 12. Figure 12 One-sided clamped IRS dam. Inflatable rubber dams and weirs are retaining two different water levels. The weirs and dams are mainly loaded by a horizontal load that results from the head difference over the IRS. In order to retain this load, stiffness has to be formed in the IRS by compressing the filler medium. The rubber sheet is then loaded by the internal pressure and the external hydraulic loads. Also stresses are present in the rubber sheet, forming the so-called membrane forces. The membrane forces make that an equilibrium exists between the internal pressure, the weight of the sheet and the external loads. The membrane forces are tension forces transferring the resulting load to the foundation. Inflatable rubber dams and weirs are designed such that this load transfer occurs in the cross section of the IRS. As an example the global equilibrium of an inflatable weir is considered, see Figure 12. A horizontal load H is present as a result of the head difference over the IRS. Figure 13 Global equilibrium inflatable weir ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics). The forces in the supports (clamp lines) can be decomposed in a horizontal and a vertical component. The distribution of the horizontal load H over both the supports is determined by the angles φ of the sheet at the supports. The largest part of the load H is distributed to the support with the smallest angle φ. In formula form this can be described by: Where: RH 1, RH 2 = the horizontal load in the supports [kn/m] Φ 1, Φ 2 = the angle between the sheet and foundation in the supports [radians] T = the membrane force [kn/m] 10 Master thesis Application of an IRS in a navigation lock

25 3.2 STATE OF THE ART: RAMSPOL BARRIER The Ramspol barrier has been in use from 2003 and is still the world wide state of the art for IRSs applied in a hydraulic environment. The Ramspol barrier is a storm surge barrier that is located in the parallel waterways Ramsdiep and Ramsgeul (these waterways are separated by a levee). Two of the three IRSs of the Ramspol barrier are located in the Ramspol and the third is located in the Ramsdiep. Figure 14 shows the Ramspol barrier during the inflated state. Figure 14 Ramspol barrier during the inflated state ([L6] Bouwdienst Rijkswaterstaat). The Ramspol barrier is a unique structure because of among others the following features 1 : The design head difference of 4,4 meter is the largest head difference for an IRS dam or weir. The length of the IRSs of 78 meter, base width of 13 meter and crest height of 8 meter. A combination of an air and water filler. The applied combination of fillers, base width and internal pressure are leading to the smallest width of the rubber sheet for the desired crest height. Furthermore, because of the combined filler the stress in the rubber sheet is limited. The unique bottom recess with rollers. The rollers are applied to accommodate space for the rubber sheet and favour an equal distribution of the sheet over the bottom recess. The required maximum probability of failure of the sheet of 1*10-5. The combination of the fillers and the bottom recess with the rollers are clearly visible in the cross section of the Ramspol barrier in Figure 15. Figure 15 Cross section Ramspol barrier ([L6] Bouwdienst Rijkswaterstaat). Throughout the design of the IRS Lock the knowledge and experiences from the design and construction of the Ramspol barrier has been used as a reference. More specific properties of the Ramspol barrier are described later. 1 [L6] Bouwdienst Rijkswaterstaat, Kennis- en Ervaringsdocument Balgkering Ramspol, December Steffen Woudstra

26 3.3 EQUILIBRIUM IN THE RUBBER SHEET As described before an equilibrium exists in the sheet. In this paragraph the equilibrium is mathematically described. The rubber sheets used for IRSs are considered to have no bending stiffness. The shape of sheet, and therefore the shape of the total IRS, results from the loads acting on the sheet. In structural mechanics, mathematical descriptions of the mechanics of flat plates are available. Plates are defined as plane elements with a small thickness compared to the planar dimensions (thickness/width < 0,1). The plate theory transforms specific 3D elements into a 2D-problem. Usually distinction is made between plates, shells and membranes. In plates and shells the load is transferred by bending stresses and in-plane stresses. In membranes the loads are only transferred by in-plane stresses. The bending stiffness of the rubber sheet used for the IRS is usually that small that it can be neglected. Only in-plane stresses will occur and the rubber sheet behaves like a membrane. Hence, membrane theory is applicable on IRSs D-static equilibrium for an IRS (single curved membranes) The sheet of an IRS is loaded by the internal pressure in the filler, the external water pressure and the weight of the sheet. An impression of the pressures acting on the sheet of an IRS is given in Figure 16. The water and air pressures are acting perpendicular to the sheet. The atmospheric pressure has no influence in the equilibrium. Therefore the size of the pressures is given relative to the atmospheric pressure. Figure 16 Pressure and weight acting on a cylindrical IRS ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics). An equilibrium exists in the sheet formed by the loads and the membrane force. Parbery derived a set of differential equations for the equilibrium using membrane theory 2. The derivation of the equilibrium equations of Parbery is described. A vertical cross section of a uniform, cylindrical IRS is considered. Each part of the sheet has such a shape that an equilibrium is present in the sheet. Parbery describes the equilibrium in small elements of the vertical cross section of the sheet. The elements are curved in only one direction. In Figure 17 such an element and the loads acting on the element are given. 2 [L7] R.D. Parbery, A continuous method of analysis for the inflatable dam, Master thesis Application of an IRS in a navigation lock

27 S is the coordinate in warp direction of the rubber sheet. The static equilibrium of an element of the rubber sheet with unloaded length ds and loaded length ds* is given for the limit case ds* 0. Figure 17 Loads on a rubber element ([L7] Parbery). In tangential direction the membrane force T is making equilibrium with the weight of the sheet w. Mathematically this is described as: For small elements, dφ is very small. Hence, cos(dφ) is more or less equal to zero. The equation becomes: From the last equation is obvious that in case the weight of the sheet is neglected the membrane force is constant. In radial direction the membrane force is in equilibrium with the resulting pressure p and the weight of the sheet: dφ is very small for small elements, so sin(dφ) is more or less equal to dφ and dφ.dt is more or less 0. The equation becomes: Where: T = membrane force in hoop direction (normal force) [kn/m] w = weight rubber sheet per meter length [kn/m] p = resulting pressure on rubber (difference between internal and external pressure) [kpa] Steffen Woudstra

28 The curvature κ of the rubber sheet is given by: In case the weight is neglected the following expressions for the membrane force can be found: This equations is the general equilibrium equations for a single curved membrane loaded by an internal and external pressure. By rewriting this equilibrium equation the angle dφ can be found for each element of a rubber sheet. Hence, also the shape of the sheet can be found. The angle dφ of each element is described by: The geometrical boundary conditions for the rubber sheet are known, these are the locations of the connections of the sheet to the foundation. The geometrical boundary conditions are: Where: L = the circumferential length of the sheet, or width of the flat sheet [m] B = the base width of the IRS, which is the distance between the two parallel clamp lines [m] Finding the shape for the 2D static equilibrium With the above membrane equilibrium equation the shape and membrane force of a single curved IRS under static loads can be found. The procedure of solving the membrane equations starts with dividing the sheet into small connecting line elements. An initial angle φ and the constant membrane force T are estimated for the first element in one of the boundaries. The boundaries (locations of connections), the width of the sheet, the internal and the external pressures are known and fixed input in the solving procedure. With help of the membrane equilibrium equation the location and angle of each connecting element of the sheet is determined. This leads to the equilibrium shape of the IRS. The initial membrane force T and angle φ are adjusted until an equilibrium is found that is in accordance with the geometrical boundary conditions. This iterative process can be easily executed with the help of a computer program. During the design phase of this thesis an Excel spreadsheet has been used for the execution of the iterative calculations. 14 Master thesis Application of an IRS in a navigation lock

29 D-static equilibrium (double curved membranes) Previously the rubber sheet has been modelled as connecting line elements in order to find the shape of a single curved cross section. A similar approach can be used for finding the shape for double curved elements of the sheet. In this approach the sheet is modelled as small plates joined together. Since the sheet is considered as a membrane, only in-plane stresses will occur. The in-plane stresses consist of normal stresses and shear stresses. In the principal directions of the curvature of an element the shear stresses are zero and hence will not contribute to the force transfer. Thus, only the normal stresses remain. These stresses occur in the principal directions, called the meridional and hoop direction. A double curved membrane element as in Figure 18 is considered. Figure 18 Normal forces in a double curved membrane loaded by an internal overpressure. For double curved membrane elements only considering normal stresses, a general membrane equilibrium equation exists: Where: R 1 and R 2 = main radii of curvature [m] T θ = the normal force in meridional direction [kn/m] T φ = the normal forces in the hoop direction [kn/m] In the above equilibrium equation the weight of the membrane elements is neglected and therefore the membrane force T is constant in both directions. In meridional direction the force per meter width is: Steffen Woudstra

30 In the hoop direction the force per meter width is: A cylindrical IRS with spherical ends is used as an example for explaining the load transfer in an IRS as a hole. The IRS is shown in Figure 19. The midsection and ends are having the same constant radius, R. The IRS is filled with air and surrounded by air. Figure 19 Example IRS for the explanation of the equilibrium in an IRS. The cylindrical midsection of the IRS is curved in only one direction. The curvature exists in hoop direction and has a constant radius R 2. It is obvious that no curvature exists in the other direction, and R 1 =. Filling in R 1 = in the membrane equilibrium equations for the double curved membrane logically leads to the membrane equilibrium equations for a single curved membrane. For the spherical ends of the IRS the sheet is double curved. Since in the example the radius for both curves are equal (R = R 1 = R 2 ) the membrane force for both the hoop and meridional direction becomes: It follows that the membrane force in both directions at the ends is half the membrane force in the midsection. Because of the double curved ends, a membrane force in the meridional direction in the ends leads to a tension force in the longitudinal direction of the IRS. For air inflated beams this longitudinal tension is used for pre-tensioning the inflatable beam. For the cylindrical IRS in Figure 19 the final membrane forces in the sheet are given in Figure 20. Figure 20 Force distribution in example IRS. 16 Master thesis Application of an IRS in a navigation lock

31 3.4 SHAPE OF THE SHEET In paragraph 3.3 general membrane equilibrium equations are given for an IRS. The equations are giving the membrane force as a function of the curvature and the resulting pressure on the sheet. By rewriting the equations the curvature on the sheet can be described. For a single curved membrane the radius of curvature is given by: The radius of curvature is a function of the resulting pressure and the membrane force. In case of an IRS applied in a hydraulic environment, the resulting pressure p can vary along the sheet. Since the weight of the sheet has been neglected, the membrane force T φ is constant along the sheet. Therefore, the radius of curvature R 2 will vary along the sheet. Three situations can occur: 1) p internal > p external p > 0: the sheet will be curved towards the inner side of the IRS 2) p internal = p external p = 0: the sheet is straight 3) p internal < p external p < 0: the sheet will be curved towards the outer side of the IRS All three situation can occur in the cross section at the same time, but along different parts of the sheet. In the IRS Lock the IRS will be submerged in the lock chamber. An overpressure will be applied in the total IRS. Due to the varying resulting overpressure over the height, the radius of curvature will be smaller in the top of the IRS than at the parts closer to the bottom. An impression for the situation in the IRS Lock is shown in Figure 21. During the inflation of the IRS the internal air pressure will be lowered. Then all the three situations given above can occur. Figure 21 Pressure situation for a submerged air filled IRS Dynamic loads In case of dynamic loads the IRS will deform as a function of time. The response of the IRS is influenced by the mass of the sheet and the filler medium, the mass of the external water, the stiffness of the IRS, the internal pressure and damping mechanisms. In case of a dynamic load, also inertial forces are playing a role. In addition, the membrane force T is not constant anymore when the weight of the structure is neglected. When a dynamic load is deforming the rubber sheet, the rubber sheet is interacting with the surrounding water. The movement of the IRS in the surrounding water, leads to interaction forces between the IRS and the surrounding water. Compared to regular concrete and steel structures, the response of the IRS for hydrodynamic loads can be really large. The changing structural properties (for example internal pressure) and loads make that, in fact, for each load situation a different construction results. Steffen Woudstra

32 3.5 BEHAVIOUR DURING INFLATION AND DEFLATION The inflation and deflation will be part of the levelling operations of the IRS Lock. The time needed for the lock operations should be kept as small as possible to minimize the delay for shipping. This makes the time needed for inflation and deflation is an important aspect for the economic feasibility of the IRS Lock. The behaviour of the sheet during the inflation and deflation will give insight in how much time is needed for the inflation and deflation. In comparison to existing IRSs in a hydraulic environment, the boundary condition are different in the case of an IRS lock. Inflating and deflating of the structure will be done while a vessel is present in the lock chamber and the space is restricted by the lock chamber walls. The rubber sheet may never hit vessels because of the risk of damage of the rubber sheet or vessels. During the inflation and deflation the internal pressure in the IRS is variable. As described before, the shape of the IRS, and therefore the behaviour during inflating and deflating, depends on the loads acting on the sheet Sheet behaviour during filling and emptying During the development of the Ramspol barrier scale tests have been conducted for the inflation and deflation of a large IRS in a hydraulic environment. An important difference with the case of a the IRS Lock, was the head difference over the Ramspol barrier during the deflation. The Ramspol barrier is filled through the abutments with a combination of air and water. In the case of filling with only water, the rubber sheet raises in a more uniform way over the full length of the IRSs. In the case of filling with only air, the sheet first raises close to the abutments. From the abutments the sheet rises up towards the midsection of the IRS where constriction of the flow over the barrier occurs. During the deflation of an IRS, also a difference in sheet behaviour takes place for a water and air filled structures. In the case of emptying a water filled IRS, the sheet lowers in a uniform way over the complete length of the structure. While deflating an air filled IRS, the pressure in the IRS lowers and from a certain moment the air pressure in the IRS will be smaller than the external hydrostatic pressure (starting from the bottom). As a result the rubber structure will be pushed together from the sides, see Figure 22. Figure 22 Pressure situation during deflation pushing IRS together leading to a larger height. During the inflation a similar situation occurs. First the middle part of the structure raises and the sides of the rubber sheet are pushed together. How the rubber sheet will exactly raise depends on the hydraulic boundary conditions, the distribution of the filling points and the weight and stiffness of the rubber sheet. A scale test for inflating and deflating a submerged air filled IRS has been conducted by graduation student Peet Versteegt. An overview of his model is shown in Figure 23. It is important to note that the scale model of the IRS is not especially scaled to model a certain design or structure. 18 Master thesis Application of an IRS in a navigation lock

33 Since the model is not scaled, the relevance of this scale test is questionable. Photos of the inflation process are shown in Figure 24. The deflation process is shown in Figure 25. Figure 23 Scale model P. Versteegt ([L8] P. Versteegt). During the inflation the middle part of the rubber structure is rising first. It should be noted that the model only consists of one filling point which is located in the centre of one end of the IRS model. With several filling points at several location and a regulation of the discharge through each point, it might be possible to influence the way the rubber sheet will rise. The rise of the rubber sheet could be regulated with the help of a guiding structure, but yet a guiding structure is never applied due to complexity and the necessary maintenance in places that are hardly accessible. Figure 24 Inflation of the scale model ([L8] P. Versteegt). During deflation the sheet lowers and at the same time is pushed together by the hydrostatic water pressure. The water level is not visible in the photos, otherwise it could be clearly seen that the depth above the rubber structure is not constant during both the inflation and deflation. This may form a problem for the availability of the minimum required keel clearance in the IRS Lock. Figure 25 Deflation of the scale model ([L8] P. Versteegt). Steffen Woudstra

34 3.6 SHEET MATERIAL The rubber sheet has to transfer the membrane force to the foundation of the IRS. Based on the expected membrane force the material composition of the rubber sheet is designed. The sheet of the IRS needs to be flexible to make inflating and deflating go relatively easy. A more flexible sheet also makes connection of the sheet to the foundation easier. In general a rubber sheet is used for inflatable dams and weirs. Rubber is an elastomer which in fact is a polymer with viscoelasticity. Rubber generally has a low Young s modulus and a high failure strain and also the ability to undergo a large elastic deformation compared to other materials. Rubber can be harvested in the form of latex from specific rubber trees. The latex then is refined into rubber ready for commercial use. Another type of rubber is synthetic rubber, which is produced out of petroleum by-products. Synthetic rubber has often superior properties to natural rubber, especially with respect to its thermal stability and its compatibility with petroleum products. The rubber sheet must be able to resist water, oil and other chemical substances which could possibly damage the rubber structure or influence its structural properties. Furthermore, the rubber structure needs robustness against floating debris, vandalism and loads by shipping. As the strength of a rubber sheet is normally not sufficient to transfer the membrane load, the rubber is reinforced with polymer fibres. Examples of such polymer fibres are Polyamide (Nylon), polyester, Aramid (Kevlar) or ultra high molecular weight Polyethylene (Dyneema) fibres. The strength properties of these fibres are given in Table 1. Material property Polypropeen (PP) Nylon (PA6) Polyester Kevlar Dyneema Tension strength [MPa] Failure strain [%] ,6 3,6 Table 1 Strength properties of reinforcement fabrics ((L6] Bouwdienst Rijkswaterstaat). With help of the reinforcement it is possible to give the structure anisotropic properties, which means the structural properties like strength and stiffness are different for different directions. The anisotropic properties can be helpful in creating an effective load transfer to the foundation. In case of the Ramspol barrier Nylon has been selected as a reinforcement for the rubber sheet. Nylon was selected for several reasons: The large deformation capacity (strain) of Nylon will redistribute concentrated stress peaks located in discontinuities and folds in the rubber sheet. The stiffer materials Kevlar and Dyneema should result in large stress peaks due to the large stiffness of these materials. Nylon has a relatively large strength compared to regular polymers. Nylon was applied for more or less thirty years in rubber weirs. Hence there was already a lot of experience and knowledge about the application of Nylon in rubber structures. New materials (Kevlar, Dyneema), with a larger stiffness than ever applied in rubber structures, should result in extrapolation in dimensions of existing applications with results which are hard to validate. The ability of the Nylon fibres to adhere to rubber. The rubber sheet finally applied in the Ramspol barrier consists of five layers, three layers with fibres and two synthetic rubber (EPDM) cover layers, see Figure 26. The total thickness of the rubber sheet is 16 millimetres. The weight of the sheet is 19,3 kg/m Master thesis Application of an IRS in a navigation lock

35 A short description of the five layers is given: 1) The rubber outer cover. Thickness 3,0 mm and water and UV-resistant (by adding carbon to the rubber). 2) Reinforced sheet of Nylon (Polyamide 6) between two layers of rubber each 1,4 mm thick. The thickness of the Nylon fibres can be neglected. The fibres are placed in the longitudinal direction of the barrier. 3) Reinforced sheet of Nylon between two layers of rubber. This layer is 5,4 mm thick and gives the main strength properties in the warp direction. 4) Identical to layer 2. 5) The rubber inner cover with a thickness of 2,0 mm. Figure 26 Composition rubber sheet Ramspol barrier ((L6] Bouwdienst Rijkswaterstaat). In Table 2 the initial properties of the rubber sheet used for the Ramspol barrier are given. Property Warp Longitudinal Tension strength (dry) 1870 kn/m 935 kn/m Tension strength (wet) 1602 kn/m 809 kn/m Young's modulus (dry) 5700 kn/m 3200 kn/m Young's modulus (wet) 3800 kn/m 2000 kn/m Bending stiffness more or less 15 Nm more or less 17 Nm Table 2 Properties rubber sheet Ramspol Barrier (L6] Bouwdienst Rijkswaterstaat) Lifetime prediction The lifetime of rubber sheets largely depends on ageing and the deterioration due to use of the sheet. The variety of conditions in combination with specific properties of reinforced rubber sheets are making a universal prediction of the lifetime extremely difficult. At present the lifetime of specific rubber sheets reinforced with polymer fibres is a field with a lot of unknowns. In the IRS Lock the rubber sheet will be loaded and unloaded in a cyclic way due to the ongoing lock cycles. Furthermore the intensity of inflating and deflating the IRS will be high compared to existing IRSs. Due to the repeating cyclic loads, stress concentrations can occur often in the same parts of the sheet and be concentrated in folds or stiffer parts of the sheet. Therefore it is possible that the sheet is susceptible to fatigue due to the inflation and deflation. For the Ramspol barrier test of the strength of the sheet have been conducted. For this specific case the lifetime of the rubber sheet is expected to be at least 25 years for an expected amount of use of 1,1 times a year. During the lifetime of the Ramspol barrier periodic test are executed with samples which were taken from the rubber sheet before the installation of the rubber sheet to the foundation. The samples are clamped and put under water close to the Ramspol barrier. Before the actual strength tests, the samples are loaded in a similar way as the barrier structure is loaded during the foregoing period. It is expected that with the help of these periodic test another 25 years of lifetime can be proven. Steffen Woudstra

36 3.7 FILLER MEDIUM Inflatable rubber structures can be filled with gasses, liquids or a combination of both. Due to structural reasons it could be beneficial to fill the rubber structure with a combination of a gas and a liquid. In existing inflatable rubber structures applied in a hydraulic environment usually only water and air fillers are applied. Water and air or always available close to hydraulic structures and therefore an easy obtainable and a reliable filler medium. A combination of a water and air filler is possible. In the case of the Ramspol barrier the combination of water and air is applied, a choice based on the pressure acting on the foundation, the speed of filling of the structure and practical issues during deflating of the rubber structure. The design of a rubber structure is largely related with the choice of the filler. The choice of the filler influences: The stiffness of the structure. The compressibility of air is much smaller than the compressibility of water. The compressibility of air increases when the air is pressurised, but the compressibility of the air will never be as large as the compressibility of water. The stresses in the rubber structure and at the foundation floor. The weight of air is small and the influence of the weight on the air pressure can be neglected. Thus, the air pressure can be assumed as being constant. Due to the weight of water, a hydrostatic pressure profile will result in a water filled rubber structure. The size of the overpressure on the rubber sheet influences the membrane force and the dimensions and shape of the structure, as is described later. The behaviour under dynamic loads. The weight of the filler influences the behaviour of the structure under dynamic loads like for instance wave loads or propeller wash. The behaviour of the rubber structure during inflating and deflating. For a water filled structure the sheet rises in a more uniform way than for an air filler. An air filled rubber structure can give problems during deflation. Vacuum can result in air bladders (in Dutch: luchtbellen). The filler largely influences the behaviour of the rubber sheet during inflation and deflation. The filling and emptying time. The time needed for filling and emptying the rubber structure and the volume of filler medium needed to realise the desired pressure inside the IRS. Also the properties of the compressors and/or pumps are influenced by the selection of the filler medium. Furthermore, some other aspects should be taken into account in the choice of the filler: A water filler can freeze during low temperatures. Anti-freeze substance can lower the point of freezing. The filler can influence the structural properties or effect the lifetime of the rubber sheet (for example anti-freeze substances). Possibly, a filler can even enlarge the lifetime of the rubber sheet. In several rubber dams and weirs only filled with air or water a blow-out occurred due to overpressure in the structures. After the blow-outs a total failure of the water retaining function occurred. 22 Master thesis Application of an IRS in a navigation lock

37 3.8 STIFFNESS OF IRSS The stiffness of a rubber structure in a vertical cross-section can be divided in several components 3 : The compression stiffness of the filler. The axial rigidity of the rubber sheet and the membrane force. The bending and shear stiffness of the rubber sheet in case a thick sheet is applied. Each of the components of the stiffness is described. For the determination of the components reference is made to the report Hydraulische Aspecten van balgstuwen en balgkeringen written by the Dutch Ministry of Infrastructures and Environment and WL Delft Hydraulics. Compression stiffness filler The compressions stiffness of air depends on the pressure inside the IRS. The stiffness can be enlarged by increasing the air pressure, but as a consequence the membrane force will increase and so is the pressure on the foundation. The compression stiffness of the air also depends on the radius of the rubber sheet (or volume). The larger the rubber structure, the smaller the compression stiffness. The compression stiffness of air is non-linear and leads to non-linear stiffness properties of the IRS. The compression stiffness of water is constant for fresh water without air bubbles (2,04*10 9 N/m 2 ). A water filler is nearly, and thereby often assumed, to be incompressible. In combination with the elastic IRS the IRS can never become infinitely stiff. Also, in longitudinal direction of the rubber structure the distribution of the of water volume in the structure can change. Which means that when phase differences take place in the deformation of the rubber sheet, water will be redistributed from an area with a decreasing volume into an area with an increasing volume. The axial rigidity of the rubber sheet and the membrane force. Changes in the external loads will result in an adaption of the membrane force. From equilibrium follows the larger the membrane force, the larger the external loads needs to be to deform and move the rubber sheet. Also the larger the resulting pressure, the larger the membrane force. In other words, the larger the resulting pressure, the stiffer the behaviour of the rubber structure. This relation between the resulting pressure and the membrane force is non-linear. The axial rigidity becomes smaller with an increasing radius of the IRS. Physical non-linear effects in the axial rigidity of a fibre reinforce rubber (stiffening effect) are contributing to the non-linear stiffness properties of the IRS. The bending and shear stiffness of the rubber sheet if a thick sheet is applied Bending stiffness and shear stiffness of the rubber sheet can be neglected for thin sheets. Only when the thickness of the sheet is large, the bending and shear stiffness are worth mentioning. Compared to the other stiffness components, the influence of the bending and shear stiffness of the rubber structure is small. Conclusion In short can be concluded that the stiffness of an IRS increases with an increasing overpressure inside the structure. As a result of the increasing overpressure also the membrane forces will increase. The stiffness decreases if the radius of the structure becomes larger. 3 [L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics, Hydraulische Aspecten van balgstuwen en balgkeringen, december Steffen Woudstra

38 3.9 BOTTOM RECESS In large inflatable rubber structures additional measures are needed to keep the rubber sheet stable on its location during the deflated state. If a hydraulic head is available during the deflation, a current will push the rubber sheet towards the downstream side of the foundation. To assure a free navigation dept for vessels, the rubber sheet is stored in a bottom recess. In the Ramspol barrier a bottom recess with rollers is applied, see Figure 27. The rollers are cylindrical bars being designed to roll easily around an axis. The rollers are applied to favour the distribution of the rubber sheet in the bottom recess. In a low maintenance structure like an IRS, the application of rollers that need regular maintenance may be not a perfect solution. Figure 27 Overview bottom recess Ramspol barrier ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics). In the Ramspol barrier the emptying process is started by opening valves. The air will flow out of the rubber structure by the water pressure. After that, the water is pumped out of the rubber structure under a small head difference. The current by the head difference will put the sheet horizontally downstream of the foundation, see Figure 28. Finally, the remaining water in the bottom recess is also removed by pumping, resulting in an under pressure in the bottom recess. An even distribution of the sheet in the bottom recess is more or less obtained by the application of rollers. The desired final storage of the sheet is shown in Figure 29. Figure 28 Flow pushes the rubber sheet downstream ([L9] Hollandsche Beton- en Waterbouw). Figure 29 Desired distribution sheet in bottom recess ([L9] Hollandsche Beton- en Waterbouw). 24 Master thesis Application of an IRS in a navigation lock

39 In practice the rubber sheet is not always correctly stored in the bottom recess. After a test closure of the Ramspol barrier in 2004, the sheet was unevenly distributed over the bottom rollers and part of the rubber sheet floated up due to a vacuum resulting in air bladders (the sheet was sucked together), see Figure 30. This part was hit by, luckily, a small vessel and both had no damage. After the test the contractor adapted the emptying process such that pressure management could be applied to evenly distribute the rubber sheet in the bottom recess. Later it turned out this adaption was not sufficient to prevent the formation of flaps and folds. With each deflation folds (20-30 cm) and flaps (30-60 cm) 4 remain after storing the rubber sheet in the bottom recess. Figure 30 Flap after test closure Ramspol barrier ([L9] Hollandsche Beton- en Waterbouw). In case a rubber structure is deflated in a situation with only really small or no currents, the rubber sheet will fold together at the foundation. Also in this case a bottom recess is needed to assure the sheet is stably stored and to prevent problems with shipping or movements of the rubber sheet. Experiences with the Ramspol barrier show that the stable and evenly distributed storage of the sheet cannot be assured. After deflating the Ramspol barrier visual inspections of the storage of the rubber sheet are executed by divers. Inspecting a rubber structure by divers is a large and time consuming operation. An IRS in the IRS Lock will often be inflated and deflated, inspections of the sheet by divers are too costly and time consuming. This makes improvements in the deflating process necessary. 4 [L10] M. van Breukelen, Improvement and scale enlargement of the inflatable rubber barrier concept, December Steffen Woudstra

40 4 HYDRAULIC LOADS IN NAVIGATION LOCKS In the IRS Lock idea the environment in which the IRS is located differs from the environment of existing IRSs. With the different environment also the loads acting on the IRS are different. In this chapter an inventory of the loads occurring in a navigation lock is presented. The loads are subdivided in four categories: loads by lock operations, external loads, loads by vessel movements and incidental loads. 4.1 LOADS BY LOCK OPERATIONS Gate operations can cause waves of translation and flows. Levelling operations and flushing can cause jet flows. A jet flows is a flow into a large body of water with a surplus velocity compared with the ambient fluid. Flow from a culvert and flow behind ship propellers show resemblance to jets. Jets are attracting water from the ambient fluid leading to an increase of the discharge in flow direction. The head difference over a lock chamber can produce jets during levelling operations. The combination of a head difference and slits under or along the lock gates can also result in jets. In downstream direction and due to horizontal and vertical divergence, the velocities and turbulence intensity in the jet flow are decreasing. This is called breaking of a jet flown which depends on: Influences of walls or other structures or vessel in the jet. The initial shape of the jet. The Influence of other surrounding jets. Jets can have a large influence area, especially when the cross section of the waterway is largely filled by for instance a wall or vessels (in the lock chamber). Jet flows can result in (locally) large loads on the rubber structure depending on the geometry and boundary conditions of the lock Levelling operations Filling and emptying is in general executed under free flow through openings in gates, short culverts in the lock heads or a longitudinal culvert system. During the filling and emptying process the water level in the lock chamber changes, resulting in a time-varying discharge and flow velocity through the openings, see Figure 31. At the downstream side of a filling point, breaker plates or a stilling chamber are applied to break the jet coming out of the valves. Valves in gates are normally located close to the bottom of the lock chamber to reduce the effect of the jet on the vessels moored in the lock. Normally several valves are applied in the width of a gate. The resulting jet from all valves depends on the shape, location and direction of the valves and as well on the distance between the valves. Figure 31 Jet flow behind an opening due to levelling ([L11] Bouwdienst Rijkswaterstaat). 26 Master thesis Application of an IRS in a navigation lock

41 The amount of water needed for levelling will be reduced by the volume of the rubber structure. If levelling of the water level in the lock can be done parallel with the filling and emptying of the rubber structure, the discharges possibly can be largely reduced as there might be more time will be available. Smaller discharges produce smaller jets and flow velocities. Besides the jets, waves of translations can occur during filling and emptying of the lock. The waves of translations will occur if for a short period water is added to or removed from the lock. As a result the water level in the lock chamber moves over a certain distance Gate operations Gate operations can lead to flows and waves of translation, depending on the type of gate. In Figure 32 a wave of translation is shown initialized by the opening of a lift gate. During the movement of mitre gates, flows appear around the tip of the gate, caused by water being pushed up in front of the gate (in the direction of the gate movement). Behind the gate the water pressure will be lowered. In front of the gate a positive wave of translation can occur if the gate is operated quickly. Under the same conditions a negative wave will occur behind the door. A head difference over the door ensues another wave of translation, resulting again in an increase or decrease of the head difference over the gate. As a rule of thumb for the safe mooring of vessels the slope of the water line in a lock chamber may only be one per thousand 5 (The Netherlands). If waves of translations are happening in a navigation lock, the waves propagating into the lock will partly reflect against the bow of a vessel(s) in the lock. By the reflection and propagation of waves of translations along the vessel(s), the wave heights and the slope of the water surface increases. This effect is also happening and be largest during emptying of the lock chamber and similarly in case the ratio of the wet cross section of the vessel(s) to the cross section of the water in the lock is large. Besides formation of a slope in a waterway, waves of translations are resulting in a (hydrostatic) water pressure difference along the lock. Figure 32 Wave of translation after opening a lift gate ([L11] Bouwdienst Rijkswaterstaat) Flushing In some cases navigation locks or used for flushing. During flushing large flow velocities can occur. An IRS Lock with also a flushing function could be realistic in an area with an extremely large difference in water availability, for instance between summer and winter. In periods when flushing is needed, the rubber structure is not needed anymore. Attention should be paid to the stable storage of the rubber sheet during flushing operations. 5 [L11] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 2, 2000 Steffen Woudstra

42 4.2 EXTERNAL LOADS External loads are loads from outside the lock chamber. Examples of external loads are wind generated waves, long waves and waves of translation Wind generated waves Wind generated waves (wind sea and swell) can enter a lock chamber when the lock gate is (partly) open. Normally locks are protected from large wind waves by wave breakers to reduce hindrance by waves for vessels entering the lock. That means in most locks the wind waves are only small. A submerged IRS in a navigation lock will not be directly loaded by the impact of wind waves. Wind waves in navigation locks are only relatively small compared to the depth of the lock and vertical accelerations (orbital motion) and pressure differences are likely not to have a large effect on the rubber structure. The height of the wind waves and loads by the waves in or near the lock is largely influenced by the following aspects: The approaching channel or waterway (also effecting waves of translation). The fetch and water depth will affect the wave height. So do structures like wave breakers in the approaching channel. The geometry of the area in front of the lock. If the width of the approaching channel is decreasing regularly and has closed walls, the wave height can increase with 35%. The direction of the waves compared to the centre axis of the lock chamber Long waves In long waves, that exist in tides, storm surges, tsunamis and river floods, the negligible vertical accelerations make the pressure distribution under the waves hydrostatic. In navigation locks, long waves will influence the water depth and hence water pressure in the lock chamber. In the design of navigation locks the long waves are taken into account in the boundary conditions via the highest and smallest water level wherefore locking is executed Waves of translation Waves of translations can be developed outside the lock chamber, for instance because of filling and emptying operations of other lock chambers, flushing, and during passage of shipping in junctions of waterways close to the navigation lock. Seiches in ports or other half open bays can result in waves of translations in navigation locks. Seiches are standing waves with a frequency equal to the resonance frequency of a basin and hard to predict. 28 Master thesis Application of an IRS in a navigation lock

43 4.3 LOADS BY MOVING VESSELS Movement of vessels is from a hydraulic point of view similar to the flow around a body. When water flows around a body, a water level depression around the body will occur. This water level depression takes also place along a vessels hull and is known as the primary wave. The primary wave has a wave length of about the vessels length. The primary wave starts with the front wave, followed by the depression and ending with the stern wave. Besides the primary waves, secondary waves occur originating from the hull and stern. A vessels propeller and eventually thrusters are causing a current called the propeller wash. The flow phenomena around a sailing vessel are explained in Figure 33. Figure 33 Flow phenomena around a sailing vessel ([L13] Ir. G.J. Schiereck). The primary wave leads to a return current along the vessel. The return current increases with the speed of the vessels and the ratio between the vessels wet cross-section and the waterways crosssection. The return currents due to the primary wave are causing a water level depression along the length of the vessel. The vessel is located inside this water level depression and will sink equal to the water level depression, this is called the squat of a sailing vessel. When the speed of the vessel increases, the return current will increase and so is the water level depression. This leads to a larger ratio between the ships wet cross section and the waterways cross section, and therefore again an increase of the return current. After a certain moment the return current and water level depression should theoretically increase to infinite. This occurs at the so called limit speed. In normal waterways the limit speed is usually not reached, since it requires a large engine power. In a normal waterway the ratio between the vessels wet cross section and the waterways cross section is large. In small cross-sections in a waterway, like the entrance of a navigation lock, the ratio is much smaller. When a vessel sails from a waterway into a navigation lock, narrowing of the cross section of the waterway can result in a temporary exceedance of the limit speed. In the narrow cross section of a lock the return current is more are less equally distributed along the side and bottom of the vessel. In that case the return currents can be categorized as jets along a wall. Steffen Woudstra

44 The secondary waves are much shorter than the primary wave. When vessels are entering or leaving a navigation lock with a high velocity, the secondary waves reflect against the lock gates, causing changing water levels and water pressures in front of the doors. Vessel propellers are causing the so called propeller wash, having the characteristics of a jet with large flow velocities. Additionally, some vessels have bow thrusters with similar characteristics as the vessels main propellers. The bow thrusters are directed sideways Vessels moving in and out a navigation lock The speed of vessels entering a lock normally varies largely. Generally loaded vessels are sailing with a smaller speed than unloaded vessels. Vessel velocities in locks with a spacious entrance are normally much larger than in locks with a narrow entrance and vessels increase speed with wind from across the sailing path. Velocities above the limit speed do normally not happen inside the lock chamber because the resulting waves are giving a deceleration of the sailing vessel as well as hindrance for other (moored) vessels. As a rule of thumb velocities above 4,5 m/s will never occur. 6 When a vessel enters a navigation lock, a positive wave of translation enters the lock with the sailing speed of the vessel. Along the vessel a water level depression occurs. The water level difference between the wave of translation and the water level depression can be large and has a steep profile because of the small horizontal distance over which the water level difference happens. The wave of translation in front of the vessel will reflect against the closed lock gates in the end of the lock. As a result the height of the wave of translation and the water level depression along the vessel will both reduce. While leaving the lock, a vessel needs to accelerate from zero speed and the hydraulic resistance of the small cross-section of the waterway is large in the lock. After some time the front part of the ship leaves the lock and the rear is still inside the lock. In this situation the squat of the vessel will be smaller. The water level behind the vessel will lower, because not enough water from the front enters the lock to the stern of the vessel. When the vessel completely leaves the lock, a positive wave of translation can enter the lock. Reflection occurs at the closed end of the lock and a water level almost two times the initial water level depression will occur. 4.4 INCIDENTAL LOADS Besides normal hydraulic loads and loads by movements of vessel, incidental loads can occur. During the design process of navigation locks risk of incidental loads should be taken into account. Different kinds of incidental loads are thinkable, among others: Structural failure. High water or a storm surge. Large temperature differences. Chemical substances in waterway. Vessel collision. Sinking of a vessel in the lock chamber. Ice loads. 6 [L11] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 2, Master thesis Application of an IRS in a navigation lock

45 5 PROBLEM AND OBJECTIVE In this chapter the unknowns related to the feasibility of the IRS are described. Thereafter the problem and objective of this master thesis are given. Besides that the approach used to fulfil the objective are presented. In existing IRSs in hydraulic environments (barriers, dams, weirs) the main load occurs by the head difference of the IRS. The load by the head difference acts perpendicular to the longitudinal axis of the IRS. Studies related to IRSs, so far, focussed on IRSs loaded by a head difference. In case of an IRS Lock concept, the IRS will be applied in a different hydraulic environment. The IRS will be completely submerged and the hydrostatic pressure is expected to be the main external load. Out of the previously given theoretical background an inventory of the unknowns has been made. In the scheme below the unknowns are given. The unknowns are more extensively described in Appendix 1. The numbers in the boxes in the scheme are equal to the numbers in Appendix 1 where the unknowns are described. 1) Filler medium A1.1.1 Structural design 2) Fibre reinforcement 3) Design formula A1.1.2 Structural behaviour 4) Load transfer 5) Specific loads or behaviour A1.1 Technical 6) Equipment A1.1.3 Inflating and deflating 7) Controlling inflating/deflating 8) Energy regeneration/storage Feasibility A1.1.4 Lifetime of the sheet 9) Fatigue and ageing 10) Robustness 11) Lock cycle time A1.2 Economical A1.2.1 Life cycle cost 12) Cost components 13) Optimal boundary conditions Steffen Woudstra

46 5.1 PROBLEM AND OBJECTIVE The IRS Lock is a new concept and so far no practical design has been made. Knowledge about the design of an IRS is limited. Also the situations in which the IRS is applicable are unexplored. Furthermore the effectiveness for water saving and the cost of the structure are unknown. It is not clear how, if and why the IRS Lock can be applied in practice. This situation leads to the following problem definition. Problem It is not clear why and whether the IRS Lock concept in practice is feasible. In order to solve the above problem, first it has to become clear how the IRS Lock will look like in practice. Besides that, the impact of the IRS on the functional performance of the navigation lock needs to be studied. Thus, a need exists for the development of a practical design of the IRS Lock and a study of the feasibility. This leads to the following objective of this master thesis: Objective Investigate the technical and economic feasibility of the IRS Lock. 5.2 APPROACH At first a design of the IRS Lock will be developed. A cyclic design approach will be used to develop the first design. During the development of the design more and more insight in the advantages and disadvantages of the IRS Lock will be gained. The cyclic process is used to incorporate new insights and improvements in the design. The final design will form the basis for the determination the functional performance of the IRS Lock. Based on the design and it s functional performance the technical feasibility of the IRS Lock will be assessed. The total Life Cycle Cost (LCC) of the designed IRS Lock will be estimated and based on the LCC the economic feasibility of the IRS Lock concept will be assessed. In the end will be concluded whether and why the IRS Lock is a feasible concept or not. 32 Master thesis Application of an IRS in a navigation lock

47 6 ANALYSIS OF THE IRS LOCK CONCEPT The IRS Lock idea has been found by Engineering consultancy firm Grontmij N.V.. Grontmij expects a large water saving and possibly extra benefits for the prevention of salt intrusion. In this chapter the background of the idea is given and the principle of the IRS Lock is presented. Furthermore the system and functional requirements for the IRS Lock are given. 6.1 BACKGROUND In the year 2010 Grontmij started a project for the expansion of the Eefde lock located in the Twentekanaal (The Netherlands). The Twentekanaal is a 48 kilometre long series of canals. It starts close to Eefde and is at the start connected with the river IJssel. The other end, in Enschede, is a closed end. The Eefde lock consist of a navigation lock, a pumping station and a flushing facility. The situation for the Eefde lock complex is shown in Figure 34. Figure 34 Situation Eefde lock complex ([W3] Google). The lift over the Eefde lock is usually 4 till 6 meter and the dimensions of the lock chamber are 140 by 12 meter. The largest lifts are occurring during dry periods when precipitation intensities are small. Precipitation is the main source of water for the Twentekanaal. During the dry periods the lowest water levels in the IJssel occur and the water loss per lock cycle becomes 140*12*6 = m 3. The water loss in the Eefde lock is on average 5,5*10 6 m 3 a month. During dry periods water scarcity in the Twentekanaal occurs and water is pumped from the IJssel into the Twentekanaal by the pumping station in Eefde. In Figure 35 the volumes of pumped water and the water loss in the Eefde lock are given for the period 1994 till 2004, clearly showing the need for a water saving solution. Figure 35 Pumped volume by the pumping station of the Eefde lock. Obviously pumping is usually needed from April to November. In the Eefde lock complex space for water saving solutions is limited. The IRS Lock was found for the Eefde lock complex in order to reduce the water loss with a minimum use of space. The reduction in water loss of the lock also means a reduction in the amount of water that needs to be pumped upstream. Steffen Woudstra

48 6.2 THE PRINCIPLE OF THE IRS LOCK In order to understand how the IRS Lock reduces the water loss of navigation locks, first the phases during the use of the IRS are described. Thereafter these phases will be integrated in the locking cycle. The execution process of an IRS in a lock cycle is divided in four phases: Inflation of the IRS The inflated phase Deflation of the IRS The deflated phase In each phase the shape and properties of the IRS are different. Furthermore during each phase different requirements and boundary conditions play a role. Therefore is important always to distinguish these four phases of use during the design process of the IRS Lock Integration inflation and deflation procedure in the lock cycle At first is assumed that the levelling with water and the air inside the IRS will be executed serial to each other. When a vessel is navigating upstream, the lock chamber is first filled with water, and after that the IRS is inflated. When a vessel navigates downstream first the IRS is deflated, thereafter the water is let out of the lock chamber. This sequence is beneficial for the available keel clearance above the IRS. Furthermore logically follows from benefits for the filling with water (large head available) and the deflation of the IRS (larger water pressure during emptying). The procedure for levelling for a vessel sailing upstream is given in Figure 36. Figure 36 Levelling procedure with IRS for vessel sailing upstream. 34 Master thesis Application of an IRS in a navigation lock

49 The procedure for levelling for a vessel sailing downstream is shown in Figure 37. Figure 37 Levelling procedure with IRS for vessel sailing downstream. The inflation and deflation phase are part of the levelling operations of the lock. The inflated and deflated phase are not contributing to the lock operations. The periods when the four phases of the IRS occur during the lock cycle are given, together with the lock operations, in Figure 38. Figure 38 Diagram lock operations and phases of use IRS ( [L13] PIANC (slightly adjusted). Steffen Woudstra

50 6.2.2 Reduction in the water loss For levelling in a regular lock a volume of water is needed which is equal to the horizontal area of the lock chamber multiplied by the lift. In formula form this is easily describe by: This volume is lost during lowering of the water level in the lock chamber. In case of the IRS Lock, part of the volume of water is substituted by the volume of the IRS. Now the volume needed for levelling can be described by the volume of the IRS, previously called V IRS, and the remaining volume of water that is still needed for levelling: Letting a volume of water in or out of the lock chamber and air in or out of the IRS will lead to a change of the water level inside the lock chamber. This water level change can be described by: Where: Δz levelling = the total water level change by levelling operations, which is equal to the lift [m] Δz water = the water level change by adding or removing water from the lock chamber [m] Δz IRS = the water level change by the inflation or deflation of the IRS [m] Before, the water loss in a navigation lock without an IRS but with vessels has been described as: With the use of the IRS the volume of the water loss can be written in formula form as: Potential benefits salt intrusion Most of the locks separate water with different qualities are located in coastal regions and these coastal locks separate fresh and salt water. In coastal locks in The Netherlands, tidal water level fluctuations are present. Often this water level fluctuates around the slightly fluctuating water level of the fresh waterway. This means that the higher water level can often occur at both sides of the lock (positive and negative lift). Two situations can be distinguished. Situation 1: high water at sea, and a lower water level in the fresh waterway. Situation 2: low water at sea, and a higher water level in the fresh waterway. In situation 1 the IRS will reduce the amount of salt water that is lost into the lower fresh water section. During situation 2 the IRS reduces the amount of the fresh water loss during the locking cycle. The amount of salt water entering the upper fresh water section is expected to be more or less the same as in a lock without IRS. For deep locks that are used mostly by vessels with a small draught, the IRS can be permanently inflated. When vessels are sailing from the low salt water to the high fresh water, the presence of the IRS will reduce the volume of salt water that enters the lock chamber. This lowers the salt content of the water in the lock chamber that is later mixed with the water from the fresh upper section. 36 Master thesis Application of an IRS in a navigation lock

51 6.3 SYSTEM The IRS is part of a larger macro-system. The macro-system is broken down into more manageable parts by a functional decomposition. Functional decomposition is the process of decomposing a macro-system into smaller and smaller parts. In an integral design the performance of the macrosystem is important for the performance of the designed (sub-)system and elements and vice versa. 7 A waterway with a navigational function can be categorized as a macro-systems and hence decomposed until element level. The macro-system and its parts are defined in this paragraph. The decomposed macro-system is also schematically presented in Figure 42. During the design study of this thesis the focus has been on the sub-system IRS. Macro-system The macro-system consists of the waterway in which the IRS Lock is located. The boundaries of the macro-system include the total volume of water in the waterway as well as all structures in, under, above and next to (dikes and levee) the waterway. System The system is formed by the total lock structure, included the rubber structure and structures constructed on both ends of the lock especially because of existence of the lock (approach route, guiding structures, waiting places, etc.). Sub-system The system lock is subdivided into the following sub-systems: inflatable rubber structure, lock chamber, lock gates, lock heads, filling and emptying equipment, bottom protection, mooring facilities, guiding structures, safety facilities and navigation signs. Elements The inflatable rubber structure is subdivided into elements. The main elements are the rubber sheet, connections of the sheet to the lock chamber, equipment for inflation and deflation, conduits and valves, a bottom recess to guarantee a stable storage of the sheet, and eventually an additional guiding and/or protecting structure for the rubber sheet. Figure 39 Functional decomposition of the macro-system waterway. 7 [L1] W.F. Molenaar and others, Hydraulic Structures Locks, March 2011 Steffen Woudstra

52 6.4 FUNCTIONAL REQUIREMENTS For IRSs in navigation locks no specific requirements are available from building codes. The designer of the IRS Lock will have to prove that the design for the IRS Lock is safe. As the IRS is part of the navigation lock, it can affect the safety and performance of the navigation lock as a hole. The IRS Lock has to meet the requirements for general lock chambers. The requirements that are important for the first design of the IRS Lock are given here. The requirements are following from the RAMSanalysis, which is presented in paragraph Reliability The reliability requirements follows from the water retaining function of the IRS Lock. The IRS Lock separate two different water levels. It is even possible that the IRS Lock is part a water defence system. The IRS should have no negative effect on the reliability of the water retaining function of the navigation lock. Availability The availability requirements follow from the functions passage of vessels and water management. The requirements for the passage of vessels can be described in terms of average waiting times or availability. Usually the availability requirement is based on economics. Locks for intensive commercial navigation often require a high availability of 99%. Specific situations will need appropriate norms. With the implementation of a new concept like the IRS Lock a lower availability of the lock chamber may be acceptable. Minimum keel clearance In all waterways used by vessels a minimum keel clearance always has to be present. Waterway guidelines are presenting indications of safe keel clearances for several categories of waterways. For the specific structure IRS Lock a safe keel clearance has to be determined based on the design of the IRS. The keel clearance has to be guaranteed during all phases of use of the IRS Desired design IRS From the literature study follows that in practice some problems occur in existing IRSs. It is desired to prevent these problems in the design of the IRS Lock. Therefore additional design goals are formulated: Damage of the sheet by other elements of the IRS Lock may not occur. The sheet of the Ramspol barrier was damaged by the rollers in the bottom recess. The sheet of the IRS located in Aalsmeer was damaged by the flaps covering the sheet. Stress concentrations should be limited. In the Ramspol barrier a factor of 3,65 was used to describe the size of the stress concentrations relative to the membrane force in the midsection. A design in which the sheet can be easily and quickly stored in the bottom recess is needed in order to limit the lock cycle time. In case of the IRS in Aalsmeer it can takes days to store the sheet stably under the flaps. For the Ramspol barrier the inflation takes an hour, the deflation takes a couple of hours. The sheet should be stably stored in the bottom recess and no flaps should be present. After a test closure of the Ramspol barrier a flap was present in the sheet. A small vessel hit the flap. 38 Master thesis Application of an IRS in a navigation lock

53 7 CASE FOR THE DESIGN OF THE IRS LOCK A case has been selected before the design of the IRS Lock was started. The process of the selection of the case is described in this chapter. Also a description of the case and boundary conditions is given. For more information related to the case is referred to Appendix OPTIMAL CASE SELECTION Typical for design projects is the fact that in an early stage important decision have to be made without having much knowledge about the future consequences. In this thesis a case had to be selected before a design of the IRS Lock was made. After a first design cycle it followed that the selected case was not suitable for the IRS Lock. Thereafter a second case has been selected and a new design has been made First case: Large Sea Lock Terneuzen For the IRS Lock the case could be essential for the performance and feasibility of the IRS Lock. In particular the dimensions of the lock chamber and lift are essential. The first case selection was based on a qualitative consideration of the economic and technical feasibility. Four combinations of lock types are considered, see Table 3. Recreational lock Commercial lock Inland lock Inland recreational locks: - Water loss is generally small, the IRS Lock is not expected to be economically feasible. - Small dimensions and less strict requirements make the IRS Lock technically more feasible. Inland commercial locks: - Relatively large water losses, IRS Lock might be economically feasible. - Technical challenges remain. Table 3 Feasibility potential for the four case situations. Coastal lock Coastal recreational locks: - Similar to inland recreational lock. Additionally there might be benefits from a reduction in salt intrusion (qualitative water management). Coastal commercial locks: - Similar to inland commercial locks. Additionally there might be benefits from a reduction in salt intrusion. Based on the above four combinations and the size of the water loss a coastal commercial lock is a challenging case environment. Such a case will also gives more insight in the advantages and disadvantages of the tidal movement in the waterway adjacent to the IRS Lock. A coastal commercial lock was searched with a relatively large lift. The lift will provide a free depth increasing the available keel clearance of vessels. When the IRS is only present in this free depth, the minimum keel clearance is guaranteed and the lock chamber floor does not need to be lowered. The Terneuzen Lock complex has been selected as a suitable case environment because of the relatively large available lift compared to the other coastal locks in the Netherlands. The future, socalled, Large Sea Lock will have by far the largest horizontal dimensions of the locks in the Terneuzen Lock complex. Hence, the application of an IRS in the Large Sea Lock has the largest water saving potential. Therefore, initially the Large Sea Lock has been selected as a case. Alternatives for the IRS in the Future Large Sea Lock have been developed and an alternative was selected for further elaboration. The combination of the Large Sea Lock and the selected alternative resulted in a preliminary design of the IRS Lock. Steffen Woudstra

54 First calculations of the membrane forces in the rubber sheet have been made with help of the equilibrium equations. The calculations for the Large Sea Lock are presented in Appendix 3. From the calculations follows that the membrane force in the midsection of the IRS will be 5600 kn/m for the hydrostatic pressure as only external load. After applying other external loads and safety factors, the membrane forces will be even larger. In practice the largest strength of reinforced rubber sheets available is 4000 kn/m (conveyor belts) 8. It doesn t seem economically feasible to produce a sheet with a strength of at least 5600 kn/m. During the selection of the Future Large Sea Lock the influence of the dimensions of the IRS on the membrane force were underestimated. The membrane force results from the overpressure along the sheet. Hence, a larger sheet (width) leads to a larger membrane force Second case: Eastern Lock Terneuzen In the selection of a new lock chamber use could be made of the lessons learnt during the preliminary design for the Large Sea Lock. The most important lesson learnt are: For increasing dimensions of the IRS the membrane force will also increase and finally reach a size which is larger than the limited strength of the rubber sheet. A large lock is usually also a deep lock. A larger internal pressure is needed. Several smaller IRSs can be applied in a large lock, but will lead to a smaller water saving. This makes several smaller IRSs economically less feasible than one large IRS. A ratio L/B is introduced. This ratio gives the width of the rubber sheet relative to the width between the clamp lines, see Figure 40. Figure 40 Explanation width of the sheet (L) and width between clamp lines (B). A case should be found with a small ratio L/B and large enough dimensions and lift (!) to achieve a significant water saving. As a first estimate an L/B smaller than 1,1 has been used. The small ratio L/B has several advantages: During inflation and deflation the vertical reach of the sheet is limited. Because of the minimum required keel clearance this leads to a lock chamber with a smaller depth. For a relatively small L/B the overlength of the sheet is also small. The smaller the overlength the easier the sheet can be stored during the deflated phase. Because of the small overlength only small flaps can occur (only during the deflated phase). With the above knowledge the Eastern Lock in the Terneuzen Lock complex has been selected as a case. The Eastern Lock combines smaller dimensions than the Future Large Sea Lock with a large potential water saving. 8 [L9] M. van Breukelen, Improvement and scale enlargement of the inflatable rubber barrier concept, December Master thesis Application of an IRS in a navigation lock

55 7.2 DESCRIPTION SELECTED CASE: EASTERN LOCK The goal of this thesis is to determine the feasibility of the IRS Lock concept for general navigation locks. In that context the Eastern Lock is used as a practical environment for the first design of the IRS Lock. Therefore specific properties of the Eastern Lock are not taken into account in the design study. The following properties of the Eastern Lock have been used during the design study: The functions of the lock: water retaining, ship passage. The main dimensions of the lock chamber. The hydraulic boundary condition in the Gent-Terneuzen Canal. The hydraulic boundary conditions in the Western Scheldt. The shipping intensity and properties of passing vessels Functions Terneuzen Lock complex The Eastern Lock is part of the Terneuzen Lock complex. The Terneuzen Lock complex facilitates passage for vessels from the fresh Gent-Terneuzen Canal (GTC) into the salt Western Scheldt (WS) and vice versa. The GTC is an important shipping route connecting the port of Gent with the North Sea. The GTC is also part of a shipping route connecting The Netherlands and France. Furthermore the GTC is directly connected with the ports of Antwerp, Zeebrugge and Dunkirk. An aerial view of the situation is given in Figure 41. Figure 41 Aerial view of the situation around the Terneuzen Lock complex ([W3] Google). The Terneuzen lock complex consists of three locks and a planned future lock chamber for large sea vessels (Post-panamax). The current locks individually are called Western lock, Middle lock and Eastern lock. The Large Sea lock is planned at the location of the Middle Lock, which will be demolished. In Figure 42 an overview of the lock complex is given. All three locks are having a water retaining, a ship passing and a water management function. Steffen Woudstra

56 The internal dimension of the lock chambers are presented in Table 4. A more extensive description of the current and the future lock chambers is given in Error! Reference source not found.. Length [m] Width [m] Sill depth [m] Western lock ,5 Middle lock ,63 Eastern lock ,5 Future Large Sea lock Table 4 Inner dimensions lock chambers Terneuzen lock complex Dimensions and layout of the Eastern Lock In Figure 42 an aerial view of the Terneuzen Lock complex and the Eastern Lock is given. The Eastern Lock is build especially for inland vessels and in use since the year The lock chamber can handle vessel up to CEMT class 6b. The maximum dimensions of the vessels allowed to pass the Eastern Lock are presented in Table 5. Type of vessels Length x width Draught Fresh Salt Sea Vessels 70 x 23 4 app. 3,9 Push barges 200 x 23 4,3 app. 3,9 Inland vessels 140 x 23 4 app. 3,9 Table 5 Maximum vessel dimensions Eastern Lock. The minimum depth of the Eastern Lock is located above the sill at the GTC side. The minimum depth is 4,5 meter relative to the target water level of the Gent-Terneuzen Canal. Including a keel clearance of 10%, vessels with a draught up to 4,0 meter can enter the Eastern Lock. Large bush barges are having a flat keel. In practice large push barges will enter the lock chamber extremely carefully and with a very low speed. Therefore these push barges are allowed to enter the lock chamber for a smaller keel clearance. The keel clearance of 0,20 meter for the design push barge is the smallest keel clearance allowed in the Eastern Lock. Figure 42 Aerial view of the Terneuzen Lock complex and Eastern Lock ([W3] Google). 42 Master thesis Application of an IRS in a navigation lock

57 The horizontal dimensions of the Eastern Lock are given in Figure 43. The smallest section of the lock chamber is called section A, the longest section is called section B. Figure 43 Overview dimensions Eastern Lock. The levels of the sills and bottom are presented by Rijkswaterstaat 9 and gathered in Table 6. Bottom levels of the Eastern Lock Bottom level Gent-Terneuzen Canal -4,7 m KP (KP = target level waterway) Sill Gent-Terneuzen Canal side -4,5 m KP (equals -2,37 m NAP) Bottom of the lock chamber -7,44 m NAP Sill Western Scheldt -7,0 m NAP Table 6 Features of the Eastern Lock. Other important aspects related to the layout and dimensions of the Eastern Lock are determined with help of. The aspects are described from here. Bottom level Western Scheldt The bottom level in the Western Scheldt just in front of the Eastern Lock is estimated. It will need to be at least the level of the Lower Astronomical Tide plus the draught of the design vessels included a keel clearance. Hence, the minimum depth is -7,19 m NAP. Lock gates The lock is equipped with six sets of mitre gates, double gates at both ends and double intermediate gates. Each set of gates is efficient for retaining water in only one direction. And each set of gates in the double gates are retaining in another direction. Such, the lock can retain water in two directions. Levelling system The Eastern Lock is filled and emptied through openings in the mitre gates. A calculation sheet made by Grontmij is used for determining the size of the openings that is needed in order to limit the hawser forces. In the sheet the conditions described by the guideline Design of navigation locks 10 are programmed. It has been found that a total surface of the openings of 35 m 2 is sufficient. The width of the openings of coastal locks is usually 0,5 to 0,67 of the width of the lock chamber. With 0,67 a total width of the openings of more or less 16 meter is found. Than the height of the openings is 2,2 meter in order to get a surface of the openings of 35 m 2. 9 [L14] Rijkswaterstaat, Vaarwegkenmerken in Nederland, February [L2] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 1, Steffen Woudstra

58 Minimum and maximum lockage level The minimum and maximum lockage level for CEMT class 5 and smaller is given as the 1% lowest and highest water level 11. In the Eastern Lock, which is larger than CEMT class 5, the minimum and maximum lockage levels are chosen based on the situation and boundary conditions. For the minimum and maximum water level the 1% values of the water level are used as a first estimation. These water levels are +3,40 m NAP en 2,78 m NAP. The minimum water level for which the design vessels can enter the lock chamber are: Gent-Terneuzen Canal side: +2,13 m NAP, this water level gives a depth above the sill of 4,5 meter. In the lock chamber the depth becomes 9,57 meter. Western Scheldt side: -2,5 m NAP, this water level also leads to a depth above the sill of 4,5 meter. In the lock chamber the depth becomes 4,94 meter. Vessels with a smaller draught can enter the lock chamber for lower water levels. The current levels of the bottom and sills are shown in Figure 44. Figure 44 Levels bottoms and sills Eastern Lock. 11 [L2] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 1, Master thesis Application of an IRS in a navigation lock

59 7.3 BOUNDARY CONDITIONS The Eastern Lock separates the Gent-Terneuzen Canal and the Western Scheldt. The GTC is a 32 kilometre long waterway. 16,6 km of the waterway is located in The Netherlands. The other 15,4 kilometres are located in the northern part of Belgium. In Table 7 some properties of the Gent- Terneuzen Canal are given. Boundary conditions Gent-Terneuzen Canal Target water level +2,13 NAP Deviation target water level +/- 0,25 m Depth 13,5 m in center (-11,37 m NAP) Width waterway 150 m (Dutch part) Table 7 Hydraulic boundary conditions in Gent-Terneuzen Canal. The WS estuary is 113 kilometres long and has an open connection with the North Sea and Scheldt. This makes the WS an important navigation route for vessels navigating between the North Sea and Antwerp. Because of the open connection with the North Sea, a tide exists in the Western Scheldt. The sea defences around the Western Scheldt are primary sea defences. Information on the tidal water levels is given in Table 8. The tidal water levels are determined out of measurements during the period 1987 until Western Scheldt Type tide Mean high water (m NAP) Mean low water (m NAP) Average 2,29-1,89 Neap 1,76-1,56 Spring 2,67-2,13 Table 8 Tidal water levels in the Western Scheldt at Terneuzen. 12 The water levels for spring and neap tide in the WS and the extreme water levels in the GTC are presented in Figure 45. Figure 45 Water levels for the GTC and the WS scaled in the cross section of the Eastern Lock. More information related to the boundary conditions can be found in Appendix [L15] Rijkswaterstaat, Waternormalen, Steffen Woudstra

60 8 DEVELOPMENT OF ALTERNATIVES The first step in the design process is the development of alternatives for the IRS Lock. A zero solution is used as a start. Improvements of the zero solution are purposed based on design targets and these improvements are used to develop alternatives. The best alternative has been selected with help of an Multi Criteria Analysis (MCA) and will be further elaborated during the design study. A more extensive explanation of the alternatives and results of the MCA can be found in DEVELOPMENT OF ALTERNATIVES The design of the zero solution represents a circular IRS. An impression of the cross section of the IRS in the width direction of the zero solution is given in Figure 46. The rubber sheet is attached to the lock chamber floor with the help of clamps. The clamps are connected to anchors which are poured in the lock chamber floor. The compressors needed for inflating the IRS are placed next to the lock in a building at ground level. Conduits are guiding the air from the compressors into the rubber structure. Figure 46 Impression of the zero solution of the IRS Lock. Based on the literature study and the requirements for the IRS Lock several design targets are set: The part of the water loss that can be saved should be as large as possible. The minimum required keel clearance should be as less as possible affected by the IRS. Ripples and folds, or discontinuities leading to stress concentrations should be prevented. The IRS should affect the reliability and availability of the lock chamber as less as possible. The IRS Lock should be robust and capable of resisting all loads in the lock chamber. The layout of the IRS should be designed such that the inflated IRS is as stable as possible. During the deflated phase the sheet should be stably stored. With help of the design targets the zero solution is improved. The improvements of the zero solution are leading to five alternatives. Some improvements are applicable to more than one alternative and are used in a later design phase to upgrade the best alternative. These general improvements are applicable to the rubber sheet: Application of a plate or armour layer at the top of the rubber structure to prevent damage and make the shape of the cross section of the IRS more effective. Use of stiffeners in the sheet in order to give the IRS a more effective shape. Addition of weight to the sheet in order to guarantee a stable storage in the deflated phase. A short description of the five alternatives follows. 46 Master thesis Application of an IRS in a navigation lock

61 Alternative 1: Sheet connected to the walls Figure 47 Impression alternative 1: Rubber sheet connected to the walls. In Figure 47 an impression of the cross section of the alternative Sheet connected to the walls is given. In the midsection of the IRS the sheet is connected to the lock chamber walls. At the ends the sheet is connected to the lock chamber bottom. Key features of the alternative are the simplicity of the design and the small overlength of the sheet (small ratio L/B). The small overlength will lead to limited fold formation during the deflated phase. Besides that the bottom recess will have a width equal to the width of the sheet, therefore the sheet will fit the bottom recess easily. Alternative 2: Rectangular shaped IRS Figure 48 Impression alternative 2: Rectangular shaped structure. This alternative consists of a rubber structure kept in a rectangular shape by frames. A freeboard is applied around the structure to prevent interaction with the lock chamber walls (by deformations). The rectangular shape of the rubber structure makes the potential water volume that can be saved really large. It is expected that the structure will be relatively stable. A disadvantage is that the frames need to be really stiff to prevent too much bending and besides that discontinuities in the sheet close to the frames will lead to peaks stresses. Alternative 3: IRS controlled by cables Figure 49 Impression alternative 3: Rubber structure controlled by cables. This alternative has a similar construction principle as an airbed. The shape of the structure is controlled with the help of cables. The cables can be placed at the inner or the outer side of the IRS. Steffen Woudstra

62 A freeboard is applied around the structure to prevent interaction with the lock chamber walls. The cables will transfer part of the membrane forces. The shape of the IRS is effective and deformations are limited by the cables. An important disadvantage of this alternative is the large overlength of the sheet. Folds will form during deflation and air bubbles can be left in the rubber structure. Furthermore, the cables need maintenance periodically. Besides that, stress concentration are expected in the sheet. Alternative 4: Perforated floor Figure 50 Impression alternative 4: Perforated floor. In the alternative Perforated floor the rubber structure is placed in a basement under the lock chamber. The lock floor is perforated and water can flow easily between the basement and the lock chamber. The perforated floor protects the IRS from loads by (jet) flows being present in the lock chamber. The keel clearance of vessels is always guaranteed. A disadvantage of the alternative is that the construction of the basement under the lock chamber will be really expensive. Furthermore the IRS is hard to reach for maintenance and the basement will be divided in smaller parts by columns or walls supporting the perforated floor. This limits the available space for the IRSs. Alternative 5: Flaps acting as cover plates Figure 51 Impression alternative 5: Flaps acting as side plates. In this alternative stiff flaps are connected to the lock chamber bottom by hinges. During the inflation the flaps will rotate until they reach a vertical position where the flaps are stopped. In the deflated phase the flaps should cover the rubber sheet and in this way guarantee a stable storage. Besides that, the flaps will protect the rubber sheet. A stiff plate or stiffeners on top of the structure have to prevent the formation of a large air bladder during the deflation of the structure. An important disadvantage of the alternative is that the structure will need a lot of maintenance on a periodic basis. Furthermore a lot of discontinuities are expected in the sheet leading to stress concentrations. 48 Master thesis Application of an IRS in a navigation lock

63 8.2 MULTI CRITERIA ANALYSIS ALTERNATIVES The Multi Criteria Analysis (MCA) is an analysis method that is used to compare the relative quality of alternatives. Each alternative is assessed for several criteria. Each criterion has a weighting factor, indicating the relative importance of the criterion. The relative importance of the criteria is determined by weighting the criterion against each other. The relative importance of the criteria are presented in Table 9. The criteria used in the MCA are described below. Robustness: Robustness of the structure is defined as the ability of a system to resist changes in loads or other load conditions than expected without failure to function properly. The robustness is positively influencing the reliability and availability of a structure. Maintainability: Maintainability is the ease with which a structure can be maintained. In this criterion also the expected maintenance and downtime as a result of maintenance (availability) are taken into consideration. Stability: This criterion represents the degree in which a alternative forms a stable structure in all phases of use. Constructability: Constructability defines the ease and efficiency with which a structure can be built. The total construction phase is taken into account. Volume saving: The efficiency for water saving is assessed by estimating the percentage of the water loss that can be saved with the IRS of each alternative. Operation time: A quantitative estimation of the time needed for inflating and deflating the rubber structure is made for this criterion. Fold formation and fatigue: This criterion is used to assess the sensitivity of a alternative for fold formation and fatigue. Due to fatigue the rubber structure can be damaged and folds can result in high stress peaks. Investment cost: The investment cost represent all spending before the start of the operational phase. Operational cost: The operational costs are all cost of operation and keeping the structure operational (maintenance costs). Also the economic disadvantage for shipping are taken into account in the operational cost. After the weighting factors have been determined, the alternatives have been assessed for each criterion. The assessment is relative, where the best alternative is given a 1 and the worst a 5. The total score for each criterion is multiplied by the weighting factor. The outcomes for each criterion are resulting in a total score per alternative, see Table 10. The alternative with the smallest total score is the performing best for the criteria. The assessment is described in 0. It should be noted that the determination of the weighting factors and the assessment of the alternatives by only the student is a subjective process. For projects in practice, several stakeholders judgements are taken into account to assure more general results for the weighting factors. In the context of this master thesis study the previously used method is acceptable. Steffen Woudstra

64 Weighting factor Score Operational cost Investment cost Fold formation Operation time Volume saving Constructability Stability Maintainability Robustness 5) Flaps acting as side plates 4) Perforated floor 3) Controlled by cables 2) Rectangular shape 1) Sheet connected to walls Weighting factor From the MCA follows that alternative 1 Sheet connected to the walls is the best alternative. The alternative scores slightly better than alternative 2. This alternative is further elaborated during the design study. Criterion Robustness % Maintainability % Stability % Constructability 1 1 3% Volume saving % Operation time % Fold formation and fatigue % Investment cost 1 1 3% Operational cost % Table 9 Determination of relative importance of the criteria. Criterion Robustness 9% Maintainability 15% Stability 24% Constructability 3% Volume saving 9% Operational time 15% Fold formation and fatigue 6% Investment cost 3% Operational cost 15% Total score Total score after weighting 2,30 2,42 3,33 3,06 3,88 Final ranking Table 10 Assessment of alternatives for each criterion. 50 Master thesis Application of an IRS in a navigation lock

65 9 OPTIMAL CREST HEIGHT AND SHAPE OF THE MIDSECTION OF THE IRS In this chapter the shape of the single curved midsection of the IRS is described. The midsection forms the main part of the IRS. Important design decisions are made. These decisions comprise the height of the IRS, the width of the sheet and the height of the connection of the sheet to the lock chamber walls. With help of the membrane equilibrium equations the shape of the IRS and membrane forces have been determined. It may be clear that finding the final height of the IRS, width of the sheet and the connection height is an iterative process. 9.1 WATER LEVELS FOR WHICH IRS IS USED The water levels in the GTC are important since they lead to the hydrostatic pressure acting on the IRS during the inflated phase. The water levels in the Western Scheldt or of less importance, since the IRS is deflated when the water level of the Western Scheldt is present in the lock chamber. The IRS can be used for a wide range of water levels by adjusting the internal pressure. The largest water level for which the IRS is inflated is governing for the design. Data about water levels in the Gent-Terneuzen Canal is available for the period 2000 until From the data 13 the extreme water levels in the GTC are found. The lowest water level during the period was +2,00 m NAP. According to agreements between the Dutch and Belgium government, the minimum water level that may occur in the GTC is +1,88 m NAP and the maximum water level is +2,38 m NAP. The IRS is used just before or during dry periods. Therefore the minimum water level for which the IRS can be used is the minimum water level of +1,88 m NAP. Just before expected dry periods, the IRS can be used for saving water and in this way creating a buffer volume in the GTC. Hence, it is possible the IRS is used for water levels slightly higher than the target level in the GTC. From the water level data it becomes clear that in case a larger water level than the target level is present, the discharge in the GTC is quickly enlarged by flushing. Therefore it is expected the IRS will not be used for buffering during water levels larger than the target water level of +2,13 m NAP. It is preferable to design the IRS for a wide range of water levels. Then the IRS can still be used in case of changing boundary conditions. In order to make the IRS employable in a wide range of water levels, a maximum water level of+2,25 m NAP is used. The design water levels for the inflated IRS are gathered in Table 11. Target water level Minimum water level Maximum water level Table 11 Water levels in the GTC during use of the IRS. Design water levels in GTC for inflated IRS +2,13 m NAP +1,88 m NAP +2,25 m NAP 13 [L15] VNSC, Zoutgehalte, waterstand KGTB en debiet KGT , Steffen Woudstra

66 9.2 CREST HEIGHT OF THE IRS Previously the total lost volume per lock cycle has been described by the rectangular volume created by the horizontal area of the lock chamber and the lift. The lock chamber of the Eastern Lock has a constant width. Therefore the lost volume can be described by a water loss per meter length of the lock chamber. In Figure 52 the lost volume per meter length and the saved volume per meter length are indicated. The lift is assumed to be 3,0 meter and the IRS crest height of 2,5 meter. The saved volume of water per meter length is equal to the green area under the rubber sheet. If the IRS is not used during a lock cycle, the total water loss is equal to both the red and the green area. As is obvious from Figure 52 the larger the crest height and height of the connections, the larger the water saving per lock cycle that the IRS is used. Figure 52 Explanation used terms for the water loss and saved volume by the IRS. The height of the IRS reduces the available keel clearance in the lock chamber. For now is assumed that the minimum required keel clearance is present when the height of the IRS is smaller or equal to the available lift. This assumption has been checked after the first design of the IRS was made. From the above assumption follows that a minimum lift is needed before an IRS with a certain height can be inflated. In case of the Eastern Lock the lift is fluctuating by the tidal fluctuations in the water level of the Western Scheldt. Therefore it might be possible that an IRS with a certain height can only be inflated during a limited part of the tidal cycle. A model was used for the determination of the height of the IRS, The goal is to find the height for which the largest water saving during a full tidal cycle results. A simple model is developed for a first estimation of the saved volume during a full tidal cycle. During the total cyclic design process the model can be adjusted and new elements can be added. An explanation of the most important factors taken into account in the model will follow. 52 Master thesis Application of an IRS in a navigation lock

67 9.2.1 Design model for the height of the IRS For the first estimate of the optimal height of the IRS some simplifications are made in the situation and boundary conditions. The following aspects are simplified and incorporated in the model: The availability of the minimum required keel clearance The variety of types and sizes of vessels using the lock chamber The lock cycle time and intensity of locking The water levels in the GTC and WS Minimum required keel clearance The height of the IRS reduces the available keel clearance in the lock chamber. As previously described, for the first design it is assumed that the minimum required keel clearance is always present when the height of the IRS is smaller or equal to the available lift. Variety of types and sizes of vessels The height of the IRS is first designed to be equal to the available lift. In such a situation the minimum required keel clearance for the design vessel is present. However, the lock chamber will also be used by vessels with a smaller draught than the design vessel. Then the minimum keel clearance can also be available when the IRS height is larger than the available lift. In practice this will lead to an additional water saving. In the Terneuzen lock complex three lock chambers are available. The choice which vessel will use which lock chamber is an important factor in the applicability of an IRS with a fixed height. For now, only the governing draught of the design vessels will be used in the model. The lock cycle time and the intensity of locking The time needed for a lock cycle determines the amount of lock cycles that can be executed within a full tidal period. Also the amount of lock cycles in which the IRS can be used is determined by the lock cycle time and the intensity of locking. An estimation of the average lock cycle time for the Eastern Lock is made. The following factors are taken into account: Time needed for opening or closing gates: T gates = 5 [min] Base time needed for levelling: T levelling1 = 10 [min] Additional time for levelling per meter lift: T levelling2 = 2,5 [min/m] Moving of vessels: T vessel = 5 [min] Like before for the lift the symbol z is used. With the above factors the lock cycle time for shipping in both directions becomes: The average lift is more or less 2 meter. Filling in the above values results in an average lock cycle time of 70 minutes for locking in both directions. The use of the IRS will affect the lock cycle time. When, in a later design cycle, more is known about the extra time needed because of the IRS, the lock cycle time will be adjusted in the model. For now, a lock cycle time of 70 minutes for equal navigation in both directions will be used. Based on the intensity of locking in the Eastern Lock, continuous locking is assumed in the model. Steffen Woudstra

68 The water levels in the GTC and WS The water levels in the GTC and WS are needed in the model for determining the available lift in time. In the GTC a target water level is maintained (+2,13 m NAP). The water level in the canal slightly fluctuates around this target water level. The water level in the WS is influence by the tide, set up or set off by wind and the supply of water from canals and precipitation. As a start simplified water levels for the GTC and WS are used for the model. For the GTC the target water level is used and for the WS the average tide. The average tide occurs in the period between the spring tide and neap tide. The water levels due to the astronomical tide are modelled with a sine function. The sine function does not take the daily inequality of the tide into account. From the average high water and the average low water the mean average water level and the mean amplitude are calculated. The following sine function is used to describe the tidal water levels: Where: z tide = the mean water level of the average astronomical tide: +0,2 [m NAP] A tide = the mean amplitude of the average astronomical tide: 2,09 [m] t = the time, which is 0 at the start of the tidal cycle [hours] T tide = the period of the tide: 24,84 [hours] The result for these simplified water level model can be clearly shown in a graph. In Figure 53 the graphs for water levels in the WS and the GTC are plotted. Figure 53 Water levels for an average tide in the WS and target water level in the GTC. The calculation sheet of the model is given in Appendix Master thesis Application of an IRS in a navigation lock

69 9.2.2 First results from the design model From the modelled water levels the available lift in time is easily calculated. In Figure 54 the available lift is plotted. It is obvious the lift is fluctuating in time by the tidal influence. As stated before an IRS with a certain height can only be used when the lift is larger or equal to the IRS height. In Figure 54 a horizontal line is plotted indicating an IRS height of 2,5 meter. The periods during which the lift is larger than or equal to the IRS height are indicated with P min,lift. Figure 54 Available lift in time. During the periods P min,lift a minimum lift of 2,5 meter is available. From the above follows that an IRS with a smaller crest height can be used for longer periods per tidal cycle. The disadvantage of a smaller crest height is that the volume inside the IRS is smaller. Hence, a smaller volume of water is saved per lock cycle. The height of the IRS for which the saved volume per tidal cycle is maximum leads to the design with the largest effectiveness. The optimal height for the IRS will be determined by expressing the saved volume of water per tidal cycle as a function of the height of the IRS. The IRS will be used only in the case the water level in the GTC is larger than the water level in the WS (positive lift). Thus, lifts from 0 to 4,02 meter will be taken into account for the average tide. With the previously made assumptions an IRS with a height up to 4,02 meter can be designed. The saved volume depends on the design of the IRS. As a first estimate it is assumed that the IRS will save 60% of the water loss per meter length of the lock chamber. Further it is assumed that the IRS will cover 80% of the length of the lock chamber. With these assumptions the volume saved by the IRS per lock cycle becomes: Where: B = base width of the IRS: 24 [m] H = the height of the IRS: 2,5 [m] L = the inner length of the lock chamber: 290 [m]. Filling in the above value gives V IRS = 8352 m 3. Steffen Woudstra

70 Now the saved volume can be plotted as a function of the height of the IRS. In Figure 55 the resulting plot for the absolute saved volume is given. Figure 55 First estimate saved volume per tidal cycle as a function of the height of the IRS. A larger lift is available during a shorter period. The amount of lock cycles that fit in that shorter period is smaller. In such a way an IRS with a larger height (larger volume inside IRS), which is applicable for less lock cycles, can lead to a smaller saved volume per tidal cycle than an IRS with a slightly smaller height. The saw-tooth shape of the graph can be explained by the fact that the amount of lock cycles that the IRS can be applied is rounded to full numbers. Since a lot of assumptions are done in order to find the height of the IRS, it is questionable in which extent the model represents the situation in practice. For a more realistic model the saw teeth can shift slightly to the left or right. For instance because of a longer lock cycle time due the use of the IRS. At least an indication of the optimal height can be found. A curve is fitted through the graph, see Figure 55. From the curve it becomes clear that the optimal height for the IRS is more or less 2,5 meter. A first design will be developed with an IRS height of 2,5 meter First estimation total water loss and total water saving per tidal cycle. With the model previously developed a first estimation of the total water loss during a full tidal cycle can be made. From the model follows that for a height of 2,5 meter the IRS can be applied during 8 lock cycles per tidal period. In that case a total water volume of m 3 will be saved. For continuous locking and the average lock cycle time of 70 minutes a total of 21 lock cycles is executed during a full tidal cycle. The lift at the end of each lock cycle is used for the calculation of the water loss for each lock cycle. In such a way the total water loss for all 21 lock cycles is calculated to be m 3. A first estimation of the effectiveness of the IRS during one tidal cycle becomes 66816/ = 24%. 56 Master thesis Application of an IRS in a navigation lock

71 9.3 SHAPE AND EQUILIBRIUM MIDSECTION With help of the membrane equilibrium equations the equilibrium for the IRS can be determined. The equilibrium situation will lead to a shape of the IRS and the size of the membrane force. In this paragraph the 2D static equilibrium for the single curved midsection will be determined Method An important simplification in the membrane equilibrium is that the weight of the rubber sheet has been neglected. As a result, the membrane force in warp direction is constant along the sheet. Parbery studied the influence of neglecting the weight on the shape of the cross section. He concluded that the weight was of minor influence (in the order of centimetres) 14. In the case of the IRS Lock the IRS is submerged and loaded by a hydrostatic pressure of several meter water column. The weight of a rubber sheet is really small compared to this hydrostatic pressure. As a reference, the weight of the rubber sheet of the Ramspol barrier is 19,3 kg/m 2. Compared to the weight of several meter water column in the IRS Lock, the weight is really small and therefore neglected. The process for the determination of the equilibrium shape starts with modelling the rubber sheet as connecting line elements. Input variable for the process are the constant membrane force and the angle of the first element of the sheet. The sheet dimensions, the inner pressure and the external hydraulic loads are fixed input. For each element the fixed input leads to an overpressure p. In this way an equilibrium shape is iterated. Together with the constant membrane force the angle of the next element is calculated. With the membrane equation this angle can be described as: TU Delft student Dorreman studied the values of the internal and external pressure on inflatable rubber structures. During his thesis he found the expression for the angle dφ for an element of an air filled IRS facing a hydrostatic external pressure. The equilibrium situation and expression for the angle by Dorreman are shown in Figure 56. Figure 56 Equilibrium in an element according to Dorreman 13. In Figure 56 some other symbols are used than before in this thesis report: 14 [L17] J. Dorreman, Balgstuwen gevuld met lucht en/of water, May Steffen Woudstra

72 dα = angle of the element, previously called dφ [rad] H = internal pressure, previously called p [m water column] HW = external water level measured from the level of the connections [m] y i = the height of an element above the sheet connections [m] Dirkmaat 15 put the iterative process for determining the equilibrium shape in an Excel sheet. Dirkmaat validated the sheet with help of data from scale tests and calculations by Dorreman. Also van Breukelen 16 validated the Excel sheet. The Excel sheet is slightly adjusted for the situation of submerged air filled IRS. The calculation process nor the equilibrium formulas have been changed. The sheet is used to find the static 2D equilibrium shape of the midsection of the IRS. The process is schematized in Figure 57. Figure 57 Schematization iterative process for finding the 2D static equilibrium Filler medium The type of the filler medium has a large impact on internal pressure on the sheet and therefore on the shape and size of the membrane forces. In the IRS Lock concept initialized by Grontmij the IRS is filled with air. Because of the importance of the filler medium, it has been checked if an air filler is the best solution for the IRS Lock. In case of only a water filler, water is saved by simply pumping water into and out of the IRS. This way of water saving can also be executed without the use of an IRS. A combined water and air filler has structural benefits, but a more complex filling and emptying system is needed. The use of only an air filler has economic advantages. Among others a shorter duration of the filling and emptying process is expected. Therefore, in accordance with the initial idea of Grontmij, has been concluded that an air filler is the best alternative. A more extensive consideration of the different types of fillers can be found in Appendix Result 2D static equilibrium for the IRS in the Eastern Lock The Excel sheet of Dirkmaat is slightly adjusted for the situation of a submerged IRS. Fundamental calculations are not changed. With the adjusted sheet a first approximation for the 2D static equilibrium of the midsection of an IRS for the Eastern Lock has been made. A minimum overpressure of 0,1 bar is applied. 15 [L18] A. Dirkmaat, Balgkering het Spui, August [L10] M. van Breukelen, Improvement and scale enlargement of the inflatable rubber barrier concept, December Master thesis Application of an IRS in a navigation lock

73 The governing maximum water level for which the IRS is used will be applied (+2,25 m NAP). The depth above the lock chamber floor becomes 9,69 meter. The input that leaded to the equilibrium is gathered in Table 12. Equilibrium input for Eastern Lock Water depth 9,69 m Sheet width 24,7 m Base width 24 m Inner pressure 1,07 bar Membrane force 930 kn/m Angle initial element 2,79 rad Table 12 Equilibrium input for the Eastern Lock. The resulting equilibrium shape is plotted in Figure 58. A crest height of 2,51 meter was reached and a membrane force of 930 kn/m occurs. Figure 58 Shape of the sheet for the Eastern Lock. The equilibrium in the sheet depends on the loads acting on the sheet. In practice the IRS can be used during lower water levels and then the external hydrostatic pressure at the lock chamber bottom will be smaller. In such a situation also the internal pressure in the IRS will be lowered with the same amount as the hydrostatic pressure. Hence, the overpressure along the sheet, and therefore the membrane force, will not change. In Figure 59 the overpressure along the sheet is plotted. It is obvious the overpressure varies along the sheet. In case a larger overpressure is applied, the overpressure at the bottom will become larger relative to the overpressure at the top. Therefore a different equilibrium shape and membrane force will result. Figure 59 Overpressure along the sheet in the Eastern Lock. Steffen Woudstra

74 10 HYDRAULIC LOADS IN THE IRS LOCK During the literature study the loads in a lock chamber have been inventoried. Hydraulic loads occur by the weight of the water, lock operations, vessel movements and external loads from outside the lock chamber. In this chapter first for all phases of use of the IRS the loads are inventoried. After that the size of pressures and flows are calculated. Finally is described how the loads are taken into account in the design process of the IRS Lock. For a more extensive description of the used approximation formulas and calculations reference is made to Appendix LOADS PER PHASE OF USE OF THE IRS Different types of loads occurring at the same time are leading to load cases. The presence of the different loads have been inventoried for each phase of use of the IRS. The result is given in Table 13. Load Inflation phase Inflated phase Deflation phase Deflated phase Hydrostatic pressure yes yes Yes yes Gate operations no yes No yes Levelling operations no no No yes External loads no yes No yes Moving vessels no yes No yes Flushing no no No yes Table 13 Presence of hydraulic loads per phase of use of the IRS. Load cases are formed and presented in Appendix 7. An impression of the load by moving vessels is given in Figure 60. An impression of the load by the flow by levelling operations in given in Figure 61. Figure 60 Impression loads by moving vessels acting on deflated IRS. Figure 61 Jet flow through openings by levelling operations acting on deflated IRS. 60 Master thesis Application of an IRS in a navigation lock

75 10.2 SIZE OF THE LOADS In this paragraph a summary is given of the sizes of the hydraulic loads acting on the IRS. The guideline Design of navigation locks 17 gives methods for the approximation of hydraulic loads in navigation locks. Also the book Bed, bank and shore protection 18 is giving methods for the approximation of flows by vessels. After comparing the methods some small differences were found. The methods from Design of navigation locks were more conservative, which could logically be expected from a design guideline. Hence, the guideline Design of navigation locks has been used for determining of the size of all hydraulic loads Hydrostatic pressure Since the IRS is completely submerged a hydrostatic pressure is always acting on the IRS. The range of water levels on top of the IRS determines the range of hydrostatic pressures acting on the IRS. The hydrostatic pressure can be calculated with: Where: ρ = mass density of water: 1025 [kg/m 3 ] g = gravitational acceleration: 9,81 [m/s 2 ] h = water depth [m] Two situations are distinguished, the inflated and the deflated state. Inflated phase Previously it was determined that the IRS will be inflated for water levels from +1,88 m NAP to 2,25 m NAP. The lowest point of the IRS is located at the lock chamber bottom at -7,44 m NAP. The crest of the IRS is assumed to be located 2,5 meter higher at -4,94 m NAP. The hydrostatic pressure is calculated for the minimum and maximum level. The results for the pressure at the lock chamber bottom and top of the IRS are gathered in Table 14. Location Minimum water level [kpa] Maximum water level [kpa] Bottom lock chamber 93,7 (h = 9,32) 97,4 (h = 9,69) Top IRS 68,6 (h = 6,82) 72,3 (h = 7,19) Table 14 Hydrostatic pressure acting on the IRS during the inflated state. Deflated phase During the deflated phase the range of water levels upon the IRS is equal to all water levels occurring in the lock chamber. These are the levels between the minimum lockage level of -2,78 m NAP and the maximum lockage level of +3,40 m NAP. In Table 15 the results for the deflated phase are shown. Location Minimum water level [kpa] Maximum water level [kpa] Bottom lock chamber 46,9 (h = 4,66 m) 109,0 (h = 10,84 m) Table 15 Hydrostatic pressure acting on the IRS during the deflated phase. 17 [L2], [L10] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen (part 1 and 2), [L12] Ir. G.J. Schiereck, Bed, bank and shore protection, Steffen Woudstra

76 Loads by lock operations The lock operations consist of the gate operations, levelling operations and flushing. Gate operations During gate operations flows will occur through the opening between the gates. Thin jets along the gates can be present, quickly breaking in downstream direction. The influence area of these jets is often small, 1 or 2 times the height of the wet part of the gates. The IRS will not be located just behind a set of mitre gates. As the lock is equipped with ebb gates and flood gates, there is always a second set of mitre gates in between the gates that are opened and the IRS. This results in a space of at least the 20 meter between the operated set of gates and the IRS. Therefore it is not likely that the thin jets will reach the IRS. Levelling operations During levelling operations water used for filling or emptying the lock chamber is discharged through the filling and emptying openings in the lock gates. This leads to jet flows behind the openings. The openings have been designed such that the hawser forces of vessels by the flows in the lock chamber are limited. The maximum velocity of the jet flows is determined for several locations. Waves of translation can be generated in the lock chamber by the non-permanent discharge during levelling operations. Lock chambers are designed such that slopes in the water surface generally are not larger than 1. For the largest length of the lock chamber this results in a wave of translation with an amplitude of 0,15 meter and a total pressure difference of 3,2 kpa (0,032 bar). As the IRS will be less long than the lock chamber, also the pressure difference along the IRS will be smaller. The results for loads by levelling operations are gathered in Table 16. Results jet flow by levelling operations Maximum discharge 50 m 3 /s Maximum velocity just behind openings 1,4 m/s Location maximum velocity at bottom 20,4 (lowest opening at WS side) Maximum velocity at bottom 0,97 m/s (lowest opening at WS side) Velocity 20 meter behind opening 0,99 m/s Turbulence intensity jet flow 0,25 Slope by waves of translation 1. Table 16 Results from calculations jet flow by levelling operations. Flushing The Eastern Lock is, in really exceptional situations, used for flushing. During flushing a maximum discharge of 18 m 3 /s through the openings in the gates will occur. The discharge through the openings during levelling operations is maximum 50 m 3 /s and therefore levelling External loads The influence of waves of translation has already been taken into account before. For a well designed lock chamber the slope in the water surface by waves of translation will generally be no larger than 1. Long waves from outside the lock chamber are having a slope that is negligible on the scale of the lock chamber. The influence of long waves on the hydrostatic pressure is taken into account before via the minimum and maximum lockage level. Wave breakers protect navigation locks from large wind generated waves. Smaller locally produced wind generated waves do not act a load on the submerged IRS. 62 Master thesis Application of an IRS in a navigation lock

77 Loads produced by moving vessels Three governing situations are distinguished in which the design push barge is sailing: 1) The push barge is sailing into or out of the lock chamber for the smallest water level of the GTC for which the push barge may use the lock chamber (+2,13 m NAP). The IRS is deflated and the depth in the lock chamber is 9,57 meter. 2) The push barge is sailing into the lock chamber for the smallest water level of the GTC for which the push barge may use the lock chamber. The IRS is inflated and the depth in the lock chamber is 9,57 meter. 3) The push barge is sailing into the lock chamber with the lowest water level of the WS for which the push barge may use the lock chamber (-2,5 m NAP). During this water level the IRS is always deflated and the depth is 4,94 meter. Return currents For the governing situations the largest return currents occur. The return currents are calculated and gathered in Table 17. The return current leads to a friction force along the full IRS caused by the bottom shear stress. It is assumed that the return current and the slope of the energy line will be present over the full (conservatively assumed) 140 meter length of the IRS. Now, the following friction forces per meter width of the IRS are found: 1) T τ = 5,8 kn/m 2) T τ = 6,8 kn/m 3) T τ = 7,3 kn/m Jet flow by main propeller and bow thrusters design vessel For the three governing situations the maximum velocities for the jet flow caused by the vessels main propeller have been calculated. The maximum jet flow velocity by the propeller based on a propulsion power of 1200 kw per propeller and an effective propeller diameter of 1,6 meter. These specification lead to a flow velocity of maximum 8,9 m/s just behind the propeller. According to the guideline Design of navigation locks the turbulence intensity for propeller flows is 0,35 to 0,40. The horizontal distances from the propeller to the location on the top of the IRS where the flow velocity is maximum, are represented by x dp. This distance has been determined together with the maximum velocity u bp at the location x dp. The results can be found in Table 17. The flow velocity from the bow thrusters is smaller than the flow velocity from the main propellers. Therefore the flow from the main propeller is governing. It should be kept in mind that the flow from the bow thrusters can occur in all directions. Primary wave The primary wave of the vessels will lead to a local rise and fall of the water level. A quick change in the water pressure will result. For the three governing situations the pressure difference along the primary waves have been determined. The results are also gathered in Table 17. Governing situation Return current [m/s] Location max velocity flow main propeller [m] Max velocity main propeller flow on top IRS [m/s] Situation 1 1,20 34,0 1,0 5,7 Situation 2 1,44 20,0 1,7 6,3 Situation 3 1,66 8,1 4,2 3,3 Table 17 Flows by moving vessels acting a load on the IRS. Pressure change along primary wave [kpa] Steffen Woudstra

78 10.3 LOADS TAKEN INTO ACCOUNT IN THE DESIGN OF THE IRS LOCK So far the loads have been determined for the different phases of use of the IRS. The loads can also be divided in loads acting over the full length of the IRS and loads acting locally on the IRS. Loads acting on the full IRS The hydrostatic pressure is always acting on the full IRS. Furthermore the return currents by the design vessels can occur on the full IRS. The return current leads to a friction force that acts in the longitudinal direction of the IRS. Compared to the membrane forces by the internal overpressure the friction force is really small. Furthermore, a small flow from flushing can act on the full IRS during the deflated phase. Loads acting locally on the IRS The loads acting locally on the IRS are all loads by jet flows. The flows are following from the lock operations and the main propeller and bow thrusters of the vessels using the lock chamber. It is expected that the local loads will lead to a really turbulent flow situation in the IRS Lock and local deformations of the IRS Loads taken into account during the first design of the IRS Lock For the first design of the IRS the hydrostatic pressure is the most important load. The hydrostatic load is present during all phases of use and acting on the full IRS. Furthermore it is expected that the hydrostatic load will have the largest influence in the membrane stresses in the rubber sheet. The return current is also acting on the full IRS. The return current is important for a study of the global stability of the IRS and load transfer in the IRS as a hole. The loads by the return current are small compared to the loads due to the overpressure inside the IRS. The loads locally acting on the IRS or highly dynamic and important when the local stability of the IRS is studied. The loads can lead to local deformations of the IRS and a local increase of the membrane stresses. The local loads are usually taken into account in a more detailed study of an IRS. At first only the hydrostatic pressure is taken into account for the first design of the IRS. After a first design is made, calculations can be executed for several load cases. From these cases more specific information about load transfer and membrane forces will be gained. With that information the design can be further improved and detailed. Finally a design will result that is able to withstand all load cases present in the IRS Lock. 64 Master thesis Application of an IRS in a navigation lock

79 11 DESIGN LAYOUT TOTAL IRS AND SHEET In this chapter the development of a first design of the layout of the rubber sheet is described. Starting point is the calculated shape of the IRS under the hydrostatic load. The IRS is subdivided in the single curved midsection, double curved ends, and the transition section. The transition section will be located between the midsection and ends. Combining these three parts leads to a 3D layout of the IRS. From the 3D layout the dimensions of the rubber sheet are determined. The 3D layout is also forming the starting point for the design of the bottom recess and elements of the system. Furthermore, the 3D layout results in a better approximation of the potential water saving LAYOUT MIDSECTION The layout of the midsection followed from the earlier derived 2D static equilibrium. For an IRS height of 2,5 meter, a width of the rubber sheet of 24,7 meter was found in case the sheet is connected to the lock chamber bottom. With these dimensions a volume of 39,4 m 3 per meter running length is present underneath the rubber sheet at the midsection Height of the connections, width of the sheet and bottom recess Previously has been found that connecting the rubber sheet to the lock chamber walls has advantages. In Figure 62 the rubber sheet, bottom recess and height of the connections are indicated in the cross section of the Eastern Lock. The height of the top of the IRS above the lock chamber floor is fixed. When the connection height will be increased, the width of the rubber sheet decreases and the width of the bottom recess increases. Figure 62 Explanation of the dimensions of the bottom recess. Contradicting requirements are playing a role in the determination of the connections height. These requirements are: The volume under the IRS should be as large as possible, therefore the highest possible connection height is desired. A larger connection height leads to a smaller sheet width, which is cheaper. A minimum keel clearance between vessels and the sheet needs to be present during all phases of use. During the deflated phase a lower connection height is preferred, during the inflation and deflation a higher connection height is desired (smaller sheet width). The width of the bottom recess should be more or less equal to the width of the sheet in order to make the sheet fit the bottom recess easily, limit the size of folds and the time needed for the deflation. The width along the bottom recess can be adjusted by changing its shape. Steffen Woudstra

80 In order to find the most suitable solution the height of the connections and the shape of the bottom recess have been adjusted iteratively. The result is a connection height of 0,55 meter above the lock chamber floor. For this connection height the 2D-static equilibrium has been determined with help of the spreadsheet used before. A total IRS height of 2,5 meter above the lock chamber floor is desired. Hence, the height of the IRS above the connections has to be 1,95 meter. The input leading to the equilibrium is given in Table 18. Equilibrium input for Eastern Lock Connection height above bottom 0,55 m Water depth above bottom 9,69 m Sheet width 24,40 m Base width 24 m Internal pressure 1,02 bar Membrane force 1000 kn/m Angle initial element 2,86 rad Table 18 Input for equilibrium Eastern Lock for connection height of 0,55 meter. Again a minimum overpressure of 0,1 bars is applied (at the connections) and from the equilibrium a total height of the IRS above the lock chamber floor of 2,50 meter is found. In Figure 63 the shape of the rubber sheet for this equilibrium is given. Figure 63 Shape of the sheet for a connection height of 0,55 meter. For this equilibrium the volume inside the IRS becomes 43,3 m 3 /m. Compared to the first design were the sheet was connected to the lock chamber floor, an additional 3,9 m 3 per meter length of extra water saving is achieved. For a total length of the midsection of the IRSs of 150 meter (first estimate) this leads to an increase of the water saving of 585 m 3 per lock cycle. The design of the bottom recess can be found in paragraph Master thesis Application of an IRS in a navigation lock

81 11.2 LAYOUT ENDS At the ends the sheet will be connected to the bottom of the lock chamber in order to close the midsection. Besides closing the IRS, the ends should be able to transfer loads in an effective way to the lock chamber. Alternatives for the ends are developed. Discontinuities in the sheet leading to stress concentrations are as much as possible prevented Load transfer by the ends of the IRS The load transfer in the rubber sheet will happen through membrane forces. As a result of the loads and geometry of the sheet, a certain shape of the IRS will be formed leading to a certain load transfer. It should be clear that the way the loads are transferred can change in time and location. For the single curved midsection of the IRS the shape and load transfer is relatively easy to find. At the ends the rubber sheet will have a curvature in two directions during the inflated phase. This makes it harder to analytically find the shape and the way the loads are transferred. The transfer of loads should occur such that the loads are equally distributed along the clamp lines. Then no large stress concentrations occur. The internal pressure inside the IRS resists the hydrostatic pressure and the resulting membrane force will be transferred towards the clamp line. More insight in the vertical force transfer of the double curved ends can be gained with help of the hypothesis of the Rainflow analysis. The hypothesis states that like a rain flow, loads will flow along curves with the steepest ascent of a surface to its supports. The hypothesis has been formulated from studies of the load transfer in plates. In the IRS Lock the loads acting in the longitudinal direction of the IRS (among others the return currents) are expected to be small compared to the load by the hydrostatic pressure. The ends should also be able to transfer the less significant longitudinal loads. An qualitative estimation of the ability of the ends to transfer horizontal loads are made for the alternatives. During a later phase of the design the (other) load cases can be studied more extensively and in a quantitative way Selected alternatives for the ends of the IRS Several alternatives for the layout of the ends have been designed. A 3D shape has been designed based on the expected shape occurring for only the hydrostatic pressure. The ends have been assessed for the load transfer and the space occupied by the ends. The load transfer should be such that no large stress concentrations are expected and an equal distribution of the loads towards the clamp line happens. The ends should not occupy a lot of space, since the saved volume of the ends save is relatively small. The selected alternative will be described from here, an impression of the selected alternative is presented in Figure 64.For a full description of all alternatives, reference is made to Appendix 8. Figure 64 Overview of the selected alternative. Steffen Woudstra

82 The advantages of the selected variant are: In vertical direction a relatively equal load transfer will happen. The clamp line has a an elliptical shape and therefore the membrane stresses will be slightly directed towards the centreline of the IRS. The alternative consists of a relatively small end that does not occupy a lot of space. Compared to the occupied space it has a relatively large internal volume. Because of the small geometry also the deformations of the end are relatively small compared to the other alternatives. The disadvantages are: It is not exactly known in which extend the ends will be able to transfer horizontal loads to the foundation without the occurance of large membrane stresses. This should be checked with help of a 3D analysis or scale test. A first layout of the sheet for the selected end alternative has been designed. The end has a width of 24 meter and a length of 6 meter. In Figure 65 the design of the ends is given together with the dimensions. A mesh is applied to the ends in order to make the shape more clearly visible. The mesh has no further meaning. Figure 65 Dimensions of the ends of the IRS. Previously, in paragraph 9.3, the 2D-static equilibrium shape for the situation were the sheet is connected to the lock chamber bottom has been determined. This situation is equal to the situation at the start of the end. The equilibrium shape is used to describe the height of the sheet at the start of the ends. The layout of the clamp line is described with a half elliptical shape. The length of the clamp line of the end becomes 28,5 meter. 68 Master thesis Application of an IRS in a navigation lock

83 11.3 LAYOUT OF TRANSITION SECTION At the midsection the sheet will be connected to the walls at a height of 0,55 meter above the lock chamber floor. At the ends the sheet will be connected lock chamber floor. In between the midsection and the ends a transition zone is needed where the clamp line lowers from the height of 0,55 meter towards the lock chamber floor. Therefore in between the midsection and the ends the so-called transition section will be present. Because of the different geometries of the sheet at the midsection and the end, along the transition section also a transition in the membrane stresses will occur. For the transition section a straight forward and practical solution is obvious. A straight slope is applied in the clamping line. The dimensions of the sheet are designed such that the height of the IRS is constant along the transition area. As the clamp line lowers, the width of the rubber sheet increases such that enough sheet is available to achieve the constant IRS height of 2,5 meter. In Figure 66 an overview is given of the midsection, transition section and end of the IRS. The clamp line is highlighted in red. The horizontal length of the slope is at first designed to be 5 meter long. This large length results in a small inclination of the clamp line of 1:9. A small inclination and long slope are preferred, since then a more gradual transition of the membrane stresses will occur. Discontinuities on a small scale in practice will lead to stress concentrations. For the design so far it is expected that a smooth stress transition along the different section of the IRS will happen. Figure 66 Overview of the different sections of the IRS and the clamp line (in red). Steffen Woudstra

84 11.4 OVERVIEW TOTAL LAYOUT IRSS AND SHEET Combining the design of the midsection, ends and transition sections, the total layout of the IRS results. In paragraph 12.1 the length and amount of IRSs are determined based on the available space in the lock chamber and described in. In paragraph 12.1 also is explained that three IRSs will be applied. The dimensions of the three IRSs are gathered in Table 19. In order to get the desired crest height the sheet has to be longer than the inflated IRS. Length midsection [m] Total length [m] Max length sheet [m] Large IRS Two smaller IRSs Table 19 Length of the IRSs and sheets. In Figure 67 an overview of the dimensions of the smaller IRSs is given. In the side view is clearly visible how the clamp line will lower from a height of 0,55 meter in the midsection to the level of the lock chamber floor at the ends. Figure 67 Total design of the two smaller IRSs for the Eastern Lock. In Figure 68 a 3D impression of the IRS is given. Surface meshes are generated for the midsection, transition section and ends. The meshes are giving a better view of the shape of the parts of the IRS, but have no further meaning. Figure 68 3D impression of the IRS for section B of the Eastern Lock. From the layout the dimensions of the flat sheet like it will be ordered from the manufacturer follow. 70 Master thesis Application of an IRS in a navigation lock

85 Layout 2D flat sheet Large rubber sheets with dimensions similar to the IRSs are usually produced by vulcanizing rubber strips together. During the chemical vulcanisation process cross links are formed between individual polymer chains of the rubber. The vulcanizing process is executed at the rubber sheet manufacturers factory. For the IRS Lock the midsection and transition parts of the IRS can be constructed by vulcanizing rectangular shaped strips together. The joints between the strips are directed in the warp direction, parallel to the direction of the main loads in the rubber sheet The double curved ends of the IRSs are having a more complex geometry. Several configurations with rubber strips are possible for the creation of the sheet for the ends. Two straight forward configurations with parallel strips are presented in Figure 69. Figure 69 End configurations with parallel rubber strips (top view). An important difference between both the above two configurations is the amount of rubber components and the total length of the joints that need to be vulcanized. The configuration with three parallel strips is easier to construct and it is expected that the cost of the construction will be smaller. Therefore the choice of three large parallel rubber strips is chosen for the first design of the IRS. In Figure 70 a top views of the rubber structures during the inflated phase is given, the several rubber components from which the total IRS is constructed can be clearly seen. Figure 70 Top view of the IRS composed of rubber strips (inflated phase). As follows from the 3D equilibrium described during the literature study, the main membrane stresses are present at the ends in meridional and in hoop direction. In order to prevent large stresses in the joints, sufficient overlap between the strips is needed. In a later design phase an analysis of the load transfer in the ends has to be executed. Because of structural reasons it is preferred that the largest loads occur parallel to the joints. If follows from the analysis of the load transfer that the loads occur perpendicular to the joint, another configuration should be considered. Steffen Woudstra

86 The 2D flat sheet for each IRS like it will be ordered from the manufacturer is shown in Figure 71. Due to the layout of the ends in practice the sheet will never be completely flat. During transport of the sheet or placement on a flat floor there will be folds present in the sheet. In practice, the three separated parts at the ends in Figure 71 will be connected to each other. The black contours in Figure 71 represent the rubber sheet components. The red contour represents the clamp line with which the total rubber sheet will be connected to the lock chamber floor. It can be clearly seen that the flat sheet is larger than the area between the clamp lines. The overlength is needed to get the desired crest height. An overlength of 0,4 meter occurs in the width of the midsection. At the start of the ends an overlength of 0,7 meter is present in width direction. An overlength of in total 2 meter is present in the centreline in longitudinal direction (1 meter per end). With these dimensions the sheet will fit the 3D layout of the IRS during the inflated phase. Figure 71 Layout of the flat sheet (black contour) and clamp line (red contour). For the IRS in section A the length of the flat sheet will be maximum 82 meter. The IRSs in section B will be less long, and the sheet will have a maximum length of 68 meter. For all IRSs the maximum width of the sheet is 24,7 meter. In practice the sheet needs to be a bit longer and wider, because of the length of the sheet that will be located in the clamp line. From experiences with the Ramspol barrier is known that it is hard to store a large overlength of sheet equally in a bottom recess. The layout of the flat sheet and clamp line of the Ramspol barrier is given in Figure 72. The situation for the Ramspol barrier is shown in order to get more insight in the amount of overlength and the problems related to storing the sheet. It is obvious from the figure that the overlength at the midsection of the Ramspol barrier is 12 meter. This is significantly more than the overlength in the design of the IRS Lock! In case of the Ramspol barrier rollers are applied such that the large overlength of the sheet can be stably stored in the bottom recess. Figure 72 Layout sheet and clamp line Ramspol barrier. 72 Master thesis Application of an IRS in a navigation lock

87 12 INTEGRATION OF THE IRS IN THE LOCK CHAMBER In this chapter the designed IRSs are integrated in the lock chamber of the Eastern Lock. Based on the available space the amount of IRSs applied in the Eastern Lock is determined. The lengths of the midsections of the IRSs are determined such that the IRSs cover the largest area possible in the Lock chamber. After that is checked if a safe keel clearance is present during all phases of use. Also measures are given assuring the availability of the minimum required keel clearance AMOUNT AND LENGTH OF THE IRSS In Figure 73 an overview of the Eastern Lock is given. The intermediate gates separate the lock chamber in two parts and thus at least two inflatable rubbers structures are needed. The dimensions of the inflatable rubber structures are amongst others limited by the constructability of the rubber sheet. The dimensions of the sheet of the Ramspol barrier are used as a reference. The sheets of the Ramspol barrier were formed out of strips of 2,6 meter width and 23,75 meter long 19. The strips were joined together with the longest edges. In that way a sheet of 90 meter long and 23,75 meter wide was formed. It is expected that with modern technologies it is possible to construct an even larger sheet. Figure 73 Overview of the dimensions of the Eastern Lock. It is desired to save as much as possible water and therefore the IRS should be as large as possible. Because of constructability, availability and practical considerations it is decided to construct three IRSs. One IRS will be constructed in the smallest section of the lock chamber, section A. Two IRSs will be constructed in section B. With the horizontal available length in the lock chamber the dimensions of the IRSs are determined. In longitudinal direction an area of 2,5 meter in front of the ends of the IRSs is kept free. This space will be useful in case of maintenance activities and also provides a free zone between the mitre gates and the IRSs. The remaining available area in the lock chamber is 80 meter long in section A and 130 meter in section B. With a fixed length of the ends and transition sections, the remaining space for the midsections of the IRSs follows. From the dimensions and the previously determined layout of the IRSs also the volume inside the IRSs is calculated. 19 [L19] HBW, Detailontwerpnota Nylon Balgdoek, February Steffen Woudstra

88 The length of the IRSs together with the internal volume for the IRS in section A is given in Table 20. The length and internal volume per IRS in section B are given in Table 21. The rubber sheets are longer than the IRSs, because of the overlength needed to get the desired crest height. The longest part of the sheet is located in the centre line of the IRS. Section A Horizontal length [m] Maximum length of the sheet [m] Volume per meter [m 3 /m] Total volume [m 3 ] Northern end 6 7,0 31,4 188,5 Transition section ,4 206,8 Midsection ,3 2511,4 Transition section ,4 206,8 Southern end 6 7,0 31,4 188,5 Total length ,9 Table 20 Longitudinal dimensions IRS in section B. Section B Horizontal length [m] Maximum length of the sheet in [m] Volume per meter [m 3 /m] Total volume [m 3 ] Northern end 6 7,0 31,4 188,5 Transition section ,4 206,8 Midsection ,3 1861,9 Transition section ,4 206,8 Southern end 6 7,0 31,4 188,5 Total length ,4 Table 21 Longitudinal dimensions IRS in section B. As follows from the tables the lengths of the sheet that are needed are at least 82 and 67 meter. In practice the sheet needs to be a bit longer and wider, because of the length of the sheet that will be located in the clamp line. In Figure 74 an overview of the Eastern Lock with the three inflatable rubber structures is given. Figure 74 Layout Eastern Lock with three IRSs (red contours). 74 Master thesis Application of an IRS in a navigation lock

89 12.2 AVAILABILITY MINIMUM KEEL CLEARANCE DURING ALL PHASES OF USE A minimum keel clearance is required in order to lower the risk of collision of a vessel with the bottom of a waterway. The keel clearance is measured from the highest point of the bottom Minimum required keel clearance design vessel The design vessels has a draught of 4,3 meter in fresh water. A rule of thumb for the keel clearance for the design vessel is 10% in fresh water. In case of the Eastern Lock this represents 0,43 meter. For navigation locks until class 5 a keel clearance of 0,6 to 0,7 meter is indicated in guidelines 20. Because of the presence of the IRS and the vulnerability of the IRS for damage, the keel clearance for the IRS Lock is enlarged. As a first estimate a keel clearance of 1 meter is assumed above the highest level where the rubber sheet can reach. This level will be conservatively determined later Vertical reach of the rubber sheet With different load conditions the IRS will have different shapes. During the inflated phase, an overpressure is present along the full sheet. During the deflated phase, an under pressure is present along the full sheet. During the inflation and deflation phase a transition occurs. For the different conditions the highest point of the rubber sheet will be located at different levels. The shape and behaviour of the IRS during the inflation and deflation is hard to predict. The same is valid for the amount of water displaced in time during the inflation and deflation of the IRS. In order to make a safe estimate of the highest level of the sheet, a conservative approach will be used. The maximum level of the sheet will be given along the width of the lock chamber and this is called the reach of the sheet. Because of the hydrostatic external pressure and the constant internal air pressure, the sheet will in practice never be straight (unless deflated). When the sheet is assumed to be able to be straight, a larger reach of the sheet will be found than is possible in practice. Therefore the assumption leads to a conservative reach of the sheet and thereby the available keel clearance. With help of the assumption of the straight sheet and the properties of an ellipse a conservative and safe reach for the sheet has been found. The method is explained in Appendix 9. The result is shown in Figure 75. The coordinates (-12, 0) and (12, 0) represent the connections of the sheet to the lock chamber bottom. Figure 75 Vertical reach of the sheet for check keel clearance. 20 [L2] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 1, Steffen Woudstra

90 The highest point where the sheet can reach is h max,sheet = 2,92 meter above the lock chamber floor. Then the sheet has the shape of a triangle. Since the reach is determined under the assumption that the sheet can be straight, in practice the sheet will never reach outside the area under the ellipse. With the above approach it is easily checked what the maximum reach is for the different section of the IRS. For the midsection a maximum reach of 2,2 meter above the connections is found, which equals 2,75 meter above the lock chamber floor. Therefore the situation between the transition section and ends of the IRS is governing. In longitudinal direction sufficient sheet is available not to limit the maximum reach in the governing cross section The minimum required depth The required depth during all phases of use is given by: For the inflation, inflated and deflation phase the governing values determined before give: The rubber sheet and bottom recess will be designed such that during the deflated phase the sheet is stably stored at the bottom of the lock chamber. Then the sheet does not reach above the connections of the sheet to the lock chamber walls. Therefore h max,sheet = 0,55 meter. Filling in the governing values determined before gives: Per phase of use the check of the availability of the minimum required depth will be done Available water depth The governing situation for the keel clearance is formed by the combination of the lowest water level for which the design vessel can enter the lock chamber. The lock chamber bottom is located at -7,44 m NAP. In case of the IRS Lock the four phases of use are again considered. Inflated and deflated phase For each phase a certain water level is governing for the keel clearance. During the inflated and deflated phase the governing water levels are formed by the minimum water levels for which the design vessel can use the lock chamber. For the minimum water levels the depths are: Minimum water depth belonging to the inflated phase: d min,inflated = 9,57 m. This depth is available for the target water level of +2,13 m NAP in the GTC. Minimum water depth during the deflated phase: d min,deflated = 4,94 m. This depth follows from a water level of -2,5 m NAP in the WS. For these water levels the keel clearance above the sills is 0,20 meter. As described in this situation gives a conservative and safe estimation of the situation in practice. The previously determined water levels and depths are presented in Figure Master thesis Application of an IRS in a navigation lock

91 Inflation and deflation phase The inflation and deflation of the IRS will lead to a change of the water level in the lock chamber and hence the available depth in the lock chamber. In formula form this has been written before as: The size of Δh air can be calculated for the use of the three inflatable rubber structures or for the use of the IRS in section A or section B only. The largest value for Δz air gives the smallest value for Δz water and this situation is governing for the available keel clearance. The largest value for Δz air is found for section B where two inflatable rubber structures are present. The total volume inside the inflatable rubber structure in section B is divided by the horizontal surface area of section B. In that way a value of Δz air = 1,3 meter has been found (5305/(170*24)=1,3 m). The minimum lift for which the IRS will be used is 2,5 meter. Therefore Δz levelling is at least equal to 2,5 meter. The lift fluctuates in time by the tidal fluctuations in the water level of the Western Scheldt. Since Δz air is constant, the value of Δz water changes is time with the tidal fluctuations. From Figure 76 follows that in case the governing water levels for which the design vessel can enter the are used, Δz levelling has a maximum value of Δz levelling = 4,63 m. At the start of the inflation the water depth is: Filling in the governing values determined before gives: As it is hard to describe the water level change by the reduction of the volume inside the IRS (by deflating) a conservative assumption is made. It is assumed that the water displace by the IRS, Δz air, is not present at the start of the deflation. Then the water depth at the start of the deflation is equal to the depth at the start of the inflation: Figure 76 Minimum available depth for each phase of use. Steffen Woudstra

92 Check of the minimum required available depth For each phase of use will be checked if the minimum required depth, and hence the minimum required keel clearance, is available. Inflation phase The IRS is inflated after a the design vessel from the Western Scheldt has entered the lock and the levelling with water is executed. The minimum required depth is: d minkeel,inf = 8,22 m. The minimum available depth is: d min,inflation = 8,27 m. The available depth is larger than the required depth. The keel clearance is ok. Inflated phase The minimum required depth is: d minkeel,inf = 8,22 m. The minimum available depth is: d min,inflated = 9,57 m. This minimum depth is available, so the situation is ok. Deflation phase The IRS is deflated before levelling with water is executed. The minimum required depth is: d minkeel,inf = 8,22 m. The minimum available depth is: d min,deflation = 8,27 m. Even for the conservative depth of 8,27 meter the situation is ok. Deflated phase The minimum required depth is: d minkeel,def = 5,85 m. The minimum available depth is: d min,deflated = 4,94 m. The available depth is 0,91 meter to small. This situation is not ok Why the situation during the deflated phase is not ok The situation during the deflated phase is analyzed. The lock chamber bottom is located 0,44 m under the lowest sill. This 0,44 meter extra depth is available in order to lower the hydraulic resistance in the lock chamber and reduce the impact of jet flows by levelling operations on vessels. The available keel clearance for the design vessel above the lock chamber bottom was 0,64 m. For the IRS Lock the keel clearance above the lock chamber floor is enlarged to 1,0 meter. The sheet is located at 0,55 meter above the lock chamber floor. The factors can be easily added to each other, finding: 78 Master thesis Application of an IRS in a navigation lock

93 Adjustments to the design as a result of the required keel clearance The design needs to be adjusted in order to get a safe situation where the minimum required keel clearance is always available. Three measures can be taken in order to guarantee the minimum keel clearance: 1) Increase the keel clearance by allowing vessels with a critical draught only for higher water levels. Then the design push barge can only enter the IRS Lock from water levels of -1,59 m NAP in the WS. Only vessels with a s draught smaller than 3,39 meter can use the IRS Lock for the previously used minimum water level for the design vessel (-2,5 m NAP). 2) Lower the lock chamber bottom together with the complete IRS for 0,91 meter. 3) The width of the lock chamber can be enlarged and fenders are used as spacers. The extra width accommodates the curved corners of the bottom recess. Vessels will only be located above the original lock chamber bottom. The lock chamber bottom together with the IRS has to be lowered for the remaining 0,36 meter together with the clamp line and bottom recess. Because of the first measure, during water levels less than -1,59 m NAP vessels with a draught larger than 3,39 meter will use the Western Lock instead of the Eastern Lock. This will lead to a larger navigation intensity for the Western Lock during low water levels. Depending on the intensity of navigation and capacity of the Western Lock it is expected this will lead to more lock cycles with a large water loss in the Western Lock and possibly longer waiting times. The second measure will lead to an increase of the construction cost of the IRS Lock. In principle the lock chamber bottom can be further lowered. Then it is possible to apply a higher IRS with a larger internal volume, leading to a larger water saving. The third measure will lead to an increase of the construction cost of the IRS Lock. Besides the increased width will also result in a larger water loss in the IRS Lock and hence a less effective water saving solution. In practice the best measure will be selected based on economical considerations. In this master thesis the main goal is to development a design that works in practice and the determination of the feasibility of the design. It is desired to achieve a design that is effective for water saving. Therefore it is decided to lower the lock chamber bottom for 0,91 meter. The level of the lock chamber bottom becomes -8,35 m NAP. The level of the connections becomes -7,80 m NAP (0,55 m above lock chamber floor). Due to the lowering of the bottom level more depth will be available during the minimum water levels for which the design vessel can enter the lock chamber. The hydrostatic pressure acting on the IRS will increase. The (flow) loads by lock operations and moving vessels acting on the IRS will be smaller due to the increase of the available depth. New equilibrium shapes are found for the different sections of the IRS. For a 10% minimum overpressure an internal pressure of 1,17 bar is needed. Then the largest membrane force is 1250 kn/m, occurring in the midsection. Steffen Woudstra

94 12.3 OVERVIEW FINAL DESIGN IRS LOCK An overview of the total design of the IRS Lock is given in Figure 77. The level of the bottom of the lock chamber is lowered towards -8,35 m NAP. The height of the IRS is 2,5 meter and the connection height is 0,55 meter above the lock chamber floor. All other dimensions have been described previously. Figure 77 Overview total design IRS Lock. In Figure 78 the available keel clearance is presented for the governing situation with the design push barge using the lock chamber. The keel clearance above the sill is 0,20 meter. The situation for the entrance from the GTC and from the WS is schematized. In case the design push barge enters or leaves the IRS Lock at the GTC side, the IRS will be inflated. In case the design vessel enters or leaves the IRS Lock at the WS side, the IRS will be deflated. During the deflated phase the keel clearance is measured from the highest level of the clamp line. Figure 78 Available keel clearance for design vessel with draught of 4,3 meter. 80 Master thesis Application of an IRS in a navigation lock

95 13 DESIGN ELEMENTS Previously the 3D layout of the IRS has been developed. In this chapter the sheet, connections, bottom recess and pumping equipment for the IRS Lock are elaborated or more extensively described. Together with the 3D layout this chapter forms a first design of the IRS lock. The first design serves as a basis for the assessment of the functional performance of the IRS Lock SHEET The strength needed for the sheet for the IRS Lock will be considered in this paragraph. Also the lifetime of the sheet is estimated and described in this paragraph. In chapter 8 the variant for the IRS Lock was developed and improvements for the sheet were given. These improvements are considered in Appendix Strength of the sheet During the design process care should be taken of risk. Risk is defined as the product of probability of an event and its consequences. During the structural design of hydraulic structures the probability of failure plays an important role. The probability of failure contains for instance failure on strength. In structural design the probability of failure is usually calculated with help of the following limit state function: Where: R = resistance, representing the strength of the element S = the loads acting on the element For an IRS the loads and strengths consist of a lot of variables which have their own distribution function. The probability of failure is given by: Three methods are available for approximating the probability of failure. In structural design the so called Level 1 method is most often used. This method is based on safety factors and the desired situation where the resistance R is larger than the load S. Also for the IRS this method is applicable. The method contains of the following check: Or: Where: R d = the design value of the strength S d = the design value of the load R rep = the representative value for the strength S rep = the representative value for the load γ R = safety factor for the strength γ S = safety factor for load Steffen Woudstra

96 Design codes specify the safety factors for general structures and loads. For specific structures as the IRS Lock no safety factor are available. With scale models and 3D calculations more information about the strength and loads can be gained. With this information the value of the safety factors can be determined. In practice the determination of the safety factors is a hard process since different stakeholders can have different interpretations of the size of loads and the value of a safe safety factor. In case no safety factors are available, safety factors of existing IRSs can be used as a reference. For the IRS Lock the safety factors for the Ramspol barrier serve as a reference. For the strength of the sheet the parts close to the joints are governing. In the joints stress concentrations can occur. Therefore the safety factors and strengths are described for the areas of the sheet close to the joints. The representative value for the strength of the sheet is calculated after the representative value for the load, load factors and safety factors are determined Representative value for the static load For the IRS several load situations are distinguished: The static load in warp direction at the midsection and transition section The static load in warp directions at the ends The static load in longitudinal direction in all sections The values of the representative loads for each load situation will be considered here. Representative static load in warp direction at the midsection and transition section The load in the warp direction of the midsection has been determined out of the 2D-static equilibrium. The load is largest for the midsection were the sheet is connected at a height of 0,55 meter above the lock chamber bottom. This part of the sheet is located relatively high above the lock chamber floor, therefore the resulting overpressure along the sheet is largest. The value of the representative load is 1250 kn/m. Representative load at the ends The 3D equilibrium in an IRS is described in paragraph 3.3. In case of a half cylindrical IRS with spherical ends, the longitudinal tension is half of the representative load in warp direction. In design for the IRS Lock the curvature is not constant along the sheet and the curvature of the ends also differs from the curvature in the midsection. Another important difference between the ends and the midsection is that the midsection is transferring loads only in the warp direction, while the ends are transferring the loads in both warp as longitudinal direction. Also the surface area of the IRS at the ends is relatively small, what makes that the membrane force will be smaller. According to the above the load at the ends will be less than 50% of the representative load in the midsection. A factor γ end = 0,5 is used as a safe estimate. Representative load in longitudinal direction midsection Because of the closed ends of the IRS, a tension force occurs in the longitudinal direction of the IRS. For the Ramspol barrier a value of 1/3 of the load in warp direction was used for the load in longitudinal direction. In a similar way as was explained for the representative loads at the ends, it follows that a representative load of 50% of the governing load in the midsection is a safe estimate for the longitudinal tension. A factor γ longitudinal = 0,5 is used. 82 Master thesis Application of an IRS in a navigation lock

97 Safety and load factors A material factor will incorporate for the variety in strengths within the sheet material. A dynamical factor is used to incorporate the influence of dynamic loads. Also a stress concentration factor (SCF) is used, taking local stress concentrations into account. All safety factors will be considered here. Material factor It is expected that for the IRS Lock a sheet with a similar quality as the sheet of the Ramspol barrier will be used. The material factor (γ m ) used for the sheet of the Ramspol barrier was based on strength tests of the rubber sheet. The governing value of A governing value of 1,3 was found for the parts of the sheet close to the clamp line. The material factor γ m = 1,3 is used for the IRS Lock. Dynamical factor During the design of the Ramspol barrier the dynamical factor (γ dyn ) of 1,3 was determined based on tests with a scale model. The main contribution to the dynamical factor came from waves and the movement of the water filler inside the IRS. In case of the IRS Lock the dynamical loads are completely different. The largest dynamical loads will occur locally due to jet flows from propellers of vessels. As described in chapter 10 the dynamical loads are expected to be small compared to the hydrostatic load. Because of the uncertainty of the size and transfer of the dynamic loads, a factor γ dyn = 1,2 is used here. Stress concentration factor (SCF) Above the abutments of the Ramspol barrier an overlength is applied in the sheet. As a result folds are formed in which stress concentrations occur. Also close to the clamp lines stress concentrations are present due to the overlength. After a lot of discussion about the value for this factor the value of SCF = 3,65 was used. In the design for the IRS Lock some overlength is present but the overlength will not lead to folds during the inflated phase. Some stress concentration can occur close to the clamp line, especially where the transition section starts and ends. It is obvious the SCF does not need to be as large as in the design for the Ramspol barrier. A value of SCF = 1,5 should be more than sufficient. A summary of the values previously determined are given in Table 22 and Table 23. Representative static load Value [kn/m] Load in warp direction 1250 Table 22 Representative load for the strength check. Factor Value [-] Load factor end γ end 0,5 Load factor longitudinal direction γ longitudinal 0,5 Material factor γ m 1,3 Dynamical factor γ dyn 1,2 Stress concentration factor SCF 1,5 Table 23 Summary values factors in safety checks Representative value of the strength The above described representative load for the midsection leads to a design load that is larger than the design strength. The safety checks will be used to determine the minimum strength needed for the rubber sheet. When the minimum strength is determined, another rubber sheet can be designed or an existing rubber sheet can be selected for the IRS Lock. Steffen Woudstra

98 Strength for warp direction at the midsection and transition section The strength check for the warp direction at the midsection and transition section becomes: With the earlier defined values R rep becomes: 2925 kn/m. Strength of the ends and strength in longitudinal direction The strength check for the warp direction at the ends is given by: The strength check for the longitudinal direction the total IRS becomes: For both the ends and the longitudinal direction the values of R rep become: 1463 kn/m Design of the sheet It is clear a sheet should be designed with a representative strength of 2925 kn/m in warp direction and 1463 kn/m in longitudinal direction. This is more or less two times the initial strength of the sheet of the Ramspol barrier. This means the amount of nylon reinforcement in the sheet of the Ramspol barrier can be doubled in order to find a sheet that is able to resist the loads. For such a double design different layers and the thickness of the layers are given in Figure 79. The two layers with a thickness of 5,4 millimetres are providing the strength in the warp direction. The three layers of 3,7 millimetres thick are giving the sheet its strength properties in the longitudinal direction. Figure 79 Sheet design IRS Lock. Another possibility is to use a fabric reinforcement with a higher tensile strength than nylon. For instance Kevlar and Dyneema are having tensile strength more than three times larger than Nylon. At the same time Kevlar is stiffer than Nylon. The effect of the larger stiffness is that less redistribution of stresses takes place and thus locally larger stresses occurs. This will lead to a larger SCF and therefore the need for a sheet with a larger representative strength. The influence of a stiffer fabric reinforcement needs a more extensive study of the stresses in the rubber sheet. Another solution in which in different parts of the IRS different reinforcement fabrics are applied could be beneficial. In the midsection, where the membrane stresses are large, but only small stress concentrations are expected, Kevlar can be a suitable reinforcement of the sheet. At the transition and ends, where the membrane stresses are smaller but larger stress concentrations are expected, Nylon can be a better solution. Also the application of both Kevlar and Nylon needs further research. 84 Master thesis Application of an IRS in a navigation lock

99 Lifetime of the sheet The lifetime of rubber sheets for IRSs largely depends the following factors: The environment in which the IRSs are located. The loads acting on the IRS during all phases of use. The geometry of the sheet and the joints between several parts of the sheet (stress concentrations). The amount of use of the IRS and the susceptibility to fatigue and deterioration. The first three factors were previously described. The amount of use of the IRS is determined here. After that the expected lifetime of the sheet is considered. Amount of use of the IRS in the IRS Lock In the Netherlands water scarcity exists mostly during dry periods occurring in the summer months June until September. During these dry periods the IRS will be used. The amount of use depends on the intensity of locking and duration of the dry periods. Some data about the intensity of locking is available. In total lock cycles 21 were executed in the Terneuzen Lock complex in When the intensity of locking is assumed equal for all lock chambers, on average 30 lock cycles a day are executed per lock chamber. In here also lock cycles without vessels are incorporated. It should be noted that the shipping intensity in the Terneuzen Lock complex increased during the past years. The highest intensity of shipping in the Eastern Lock occurs in the period June to August. Recreational vessels are responsible for the large intensity. The intensity of recreational vessels is largest during the weekends, while the intensity of commercial vessels is largest during the week (Monday till Saturday morning). In the Eastern Lock locking is executed 24 hours a day. Continuous locking with vessels in the lock chamber can be assumed during the summer months. As is described in paragraph 14.2 the lock cycle time increases by the use of the IRS. As a result the IRS can only be applied during 6 lock cycles per tidal period in case the target water level in the GTC is present. The summer months consist of in total 122 days, which equals 118 tidal periods. The above situation leads to a potential use of the IRS in 708 lock cycles during the period June to August. When the water scarcity is assumed to be present a quarter of the time, the IRS will be used during 177 lock cycles. Consideration of the lifetime for the sheet in the IRS Lock The lifetime of specific rubber sheets and the susceptibility for fatigue is hard to determined without tests of the specific rubber sheet that will be applied in the IRS Lock. Some information about the lifetime of rubber sheets is present for reference IRSs. Since time is limited in this master thesis, a qualitative approach is used to estimate of the lifetime of the sheet for the IRS Lock. Use will be made of reference sheets for the IRSs applied in Aalsmeer and Ramspol. The IRS in Aalsmeer was the first IRS weir in The Netherlands and build in the late 60 s. It is located in the Ringvaart Haarlemmermeer polder near Aalsmeer. The IRS has been inflated during test inflations only, which were done solely once in eight years. During the deflated phase the sheet has been covered by flaps. After 40 years in the bottom recess and less than twenty inflations the sheet is degenerated. Due to ageing the quality of the sheet is insufficient for further use and thus the sheet needs to be completely renewed. 21 [L20] Rijkswaterstaat directie Zeeland, Scheepvaart in Zeeland 2008, July Steffen Woudstra

100 In the Ramspol barrier parts of the original sheet of the barrier are placed in the water close to the barrier. The properties of these parts of the sheet are being monitored. During the design of the Ramspol barrier a lifetime of the sheet of at least 25 years has been proven. Possibly the sheet can be used longer, but that will need to be proven later. The expected amount of use of the Ramspol barrier is 1,1 inflation per year. The lifetime of the sheet for the IRS Lock can be qualitatively considered now based on the factors influencing the lifetime of the sheet. The sheet for the IRS Lock is compared to the reference structures based on the four main factors determining the lifetime of the sheet. The results are gathered in Table 24. Aspect Environment Loads Geometry Amount of use Consideration aspect for the IRS Lock The reference structures are located in fresh water. Depending on the water levels the IRS Lock is located in a fresh, brackish or salt environment. It is expected the salt water will negatively influence the lifetime of the sheet. The load in the full sheet for the IRS Lock is relatively large. This is possible due to the low SCF and in principle no problem. The geometry of the IRS for the IRS Lock is simple and no folds are expected due to the geometry of the sheet and bottom recess. This makes that the geometry of the IRS positively influences the lifetime of the sheet. The IRS for the IRS Lock is inflated and deflated 177 times a year. In one year the IRS will be used much more than other IRSs in their total lifetime. The inflation and deflation and ongoing lock cycles are leading to repeating loads making the rubber sheet susceptible for fatigue and deterioration. Table 24 Qualitative consideration of the lifetime of the sheet for the IRS Lock. From the above follows that the design of the IRS is a positive aspect for the lifetime of the sheet. The environment and the amount of use are both considered to negatively influence the lifetime of the sheet. The IRS for the IRS Lock is so intensively used that the lifetime of the sheet is only estimated to be 2 years. In order to make a better prediction of the lifetime of the sheet a test sheet should be produced and loaded similar to the sheet in the design for the IRS Lock. During the use of the IRS Lock a similar procedure for the monitoring of the properties of a reference sheet as in the case of the Ramspol barrier is recommended. 86 Master thesis Application of an IRS in a navigation lock

101 13.2 CONNECTIONS In existing IRSs standard clamps are used for the connection of the sheet to the foundation of the IRS. Clamps are forming a connection that is considered to be water and air tight. A clamp consists of two plates between which the rubber sheet is placed. The plates are bolted together. With help of anchors the plates are connected to the concrete foundation. Depending on the dimensions of the clamps and the dimensions and amount of anchors, clamps can have large capacities capable of transferring large tensions forces to the foundation of an IRS. In Figure 80 a regularly applied teeth clamp is given as an example. Figure 80 Teeth clamp ([L21] HBW). In regular IRSs the clamps are attached to a horizontal foundation. In case of the IRS Lock most of the clamps are connected to the vertical lock chamber walls. Applying the standard clamps to the lock chamber walls will not result in a good solution, since the sheet will fold around the clamps during the deflated phase. Folding of the sheet will lead to wear and tear of the sheet and potentially locally a large susceptibility to fatigue in the folds. A detail of this situation is given in Figure 81. Figure 81 Detail application traditional clamp connection in IRS Lock. The described problem can be solved by the application of horizontal clamp lines. This type of clamps will give the sheet more freedom of rotation. A solution is designed and given in Figure 82. A steel L- profile is anchored with two anchors. One is applied in the lock chamber wall and the other one in the bottom recess. Obviously the bottom recess shifts towards the middle of the lock chamber with a distance equal to the width of the L-profile. The anchor in the lock chamber wall is loaded by a normal force. The anchor in the bottom recess will be loaded by shear. The membrane force is loading the clamp in a horizontal and vertical way. For the static equilibrium the horizontal load is more or less three times larger than the vertical load, depending of the angle of the sheet close to the connection. Care has to be taken during the detailing of the connections, the contribution of both anchors to the load transfer could be critical. Steffen Woudstra

102 Figure 82 IRS Lock with horizontal clamp line. In the IRS Lock the IRSs are inflated and deflated much more than in usual IRSs. As describe before a renewal of the sheet is expected to be necessary each two years. During the inflation and deflation the sheet is moving around the clamps. Because in the IRS Lock the IRS is much more often inflated and deflated than in existing rubber dams, weirs and barriers, the sheet will be more susceptible to fatigue. Two solutions are obvious for the case that fatigue close to the clamps is governing for the lifetime of the sheet: Make the sheet less susceptible to fatigue by using a higher quality rubber. The application of hinges in the connection, see Figure 83. The first solution is obvious, but limited by the material properties and structural requirements of the rubber sheet. In case hinges are applied, the rotation will be taken over by the hinge and the sheet will not fold around the connection. The application of hinges is not preferred since a complex and expensive connection is formed. Hinges also have several disadvantages, for instance the need for temporary maintenance (greasing) and inspection. In case the hinges do not work properly because of insufficient maintenance, the sheet will still be susceptible to fatigue. Figure 83 Connection with a hinge. Obviously at the ends the clamp line needs to be curved and it is desired to produce special clamps that fit the curve of the layout of the IRS at the ends. 88 Master thesis Application of an IRS in a navigation lock

103 13.3 BOTTOM RECESS The bottom recess has to provide sufficient space to store the total sheet stably between the clamp lines. The bottom recess should be designed such that the process of storing the sheet can be easily and quickly executed. In Figure 84 the flat sheet and clamp line are given, clearly showing that an overlength of sheet is present in the width and length of the IRS. Figure 84 Layout of the flat sheet (black contour) and clamp line (red contour). The bottom recess can be designed slightly larger than the rubber sheet. Then the sheet will fit the bottom recess easily. It is expected that this will reduce fold formation and makes that the sheet can be lowered and stored quickly. A larger bottom recess than the sheet will also accommodate space for short term or permanent strain of the rubber sheet Selection of an alternative for the bottom recess Space for the overlength of the sheet can be created in the bottom recess in several ways: The application of rollers, like was done in the Ramspol barrier. Applying large ripples in the lock chamber floor. Deepening the bottom recess. A combination of deepening the bottom recess and applying ripples. The Rollers for the Ramspol barrier are designed for a situation where the sheet is deflated under a head difference. The system was previously described in paragraph 3.9. In the case of the IRS Lock no head difference is present during the deflation. Besides that, the rollers need temporary maintenance and inspection, which is a disadvantage of the system. Therefore the solution with rollers is not a suitable solution for the IRS Lock. Large ripples will lead to a larger storage surface than initially available, but the ripples will not lead to a significant extra length and width along the bottom recess, unless the ripples are large (deep bottom recess). The ripples will give the bottom recess a complex shape leading to extra cost. Deepening the bottom recess will result in significantly more space for the storage of the sheet. In the midsection the bottom recess does not need to be deepened since the sheet is connected to the walls. A deep bottom recess does not need any maintenance, and the construction is relatively easy compared to the alternative with ripples. Furthermore, the deepened bottom recess leads to extra depth, which is beneficial for the available keel clearance above the sheet. The deep bottom recess is selected as the most suitable solution for the IRS Lock. The design of the bottom recess for the midsection, transition section and ends are described from here. Steffen Woudstra

104 Bottom recess at the midsection An overview of the cross section of the sheet and bottom recess in the midsection of the lock chamber is given in Figure 85. Figure 85 Overview bottom recess midsection. The equilibrium in the sheet at the midsection has been found in paragraph From the equilibrium follows that the width of the sheet at the midsection becomes 24,40 meter. A bottom recess has been designed with a total width of 24,6 meter. Hence, a small overlength of 0,2 meter is available (equal to 8 pro mille). An overview of the shape of the rubber sheet and the bottom recess at the midsection is given in Figure 86. A detail of the dimensions of the curved part of the bottom recess is given in Figure 87. Figure 86 Bottom recess and sheet at midsection. Figure 87 Detail corner bottom recess midsection Bottom recess at the transition section In the transition section the height of the connection of the sheet lowers towards the bottom of the lock chamber. Where the transition section meets the end, the width of the sheet is 24,7 meter and the overlength of the sheet is 0,7 meter in width direction. In the transition section a similar design as for the midsection has been made. As the width of the sheet increases along the transition section towards the ends, also the width of the bottom recess needs to be increasing. Because of constructability reasons it is not desired to design a lot of different shapes for the bottom recess. Therefore the shape of the bottom recess at the transition section has been designed equal to the shape of the bottom recess at the midsection. The width of 90 Master thesis Application of an IRS in a navigation lock

105 the bottom recess will be 24,6 meter while the width of the sheet at the transition section is 24,7 meter. In that case an overlength of the sheet at the transition section of 0,1 meter is present. In that situation small ripples (maximum 5 centimetres high) can occur in the sheet during the deflated state. These ripples are so small that it is not expected that they will result in problems, stress concentrations or fatigue in the rubber sheet Bottom recess at the ends At the ends the sheet will be connected to the lock chamber bottom. The lock chamber bottom is flat. An overlength of the sheet is present in both the width as the longitudinal direction. The overlength is different along the length and width of the end. If the bottom recess will have to fit the sheet exactly, the shape of the bottom recess will become really complex. The counter side of such a complex shape is that the cost of the construction of the bottom recess are large. In practice it is questionable if the complex shape will add enough extra value for being worth producing such a complex shaped bottom recess. In the economical consideration of producing the bottom recess at the end some technical questions need to be answered: Will the sheet during the deflation lower in such a way that it exactly fits the bottom recess? In which extend will the sheet be redistributed along the bottom recess during the deflation? In which extend is it in practice a problem when small folds exist in the sheet during the deflated phase? Because the above questions it is recommended to do a further study of the behaviour of the sheet during the deflation. A scale model can be used to study this behaviour. At this stage of the design study a first design is made based on constructability. At the ends the edges of the bottom recess have the same curvature as in the midsection and transition section, see Figure 88. Figure 88 Design bottom recess (blue), clamp line (red) and sheet (black) at the end. At the end the sheet is slightly larger than the space in the bottom recess. In the width direction the sheet is maximum 0,10 meter wider than the bottom recess. In longitudinal direction the sheet is 1,44 meter larger, which equals 0,72 meter per end. Small folds up to 0,36 meter are theoretically possible during the deflated phase. But at the same time is expected that the width of the sheet will limit the size of the folds. Because of the 0,55 meter deep bottom recess and the keel clearance that is guaranteed above the connections located 0,55 meter above the lock chamber floor, the small flaps will never hit vessels using the IRS Lock Volume in deep bottom recess Because the deepened bottom recess at the ends and the transition sections, the internal volumes of the IRSs will become larger. An additional volume of 150 m 3 per IRS will be present. Therefore the IRS in section A will have a volume of 3452 m 3 and the IRSs in section B will have a volume of 2802 m 3. Hence, the total volume of the three IRSs together becomes 9056 m 3. Steffen Woudstra

106 Overview of the total layout of the bottom recess In Figure 89 a side view of the IRS with the bottom recess is given. Figure 90 gives an 3D impression of the bottom recess previously designed for the different sections of the IRS. Along the clamp line the bottom recess has curved corners. The other parts of the bottom recess are planes formed by the lock chamber bottom. In the area of the transition section the lock chamber floor will be lowered from -8,35 m NAP to -8,90 m NAP. At the ends the bottom is located at -8,90 m NAP. Figure 89 Overview longitudinal cross section IRS. Figure 90 Total layout bottom recess (blue) and clamp line (red contour) Preventing wear and tear of the rubber sheet by the bottom recess It is expected that during the deflation the sheet falls downward in a vertical way. After the sheet touches the bottom recess first, it is possible that the sheet will be redistributed over the bottom recess by the water pressure and decrease of the internal pressure. Redistribution of the sheet over the bottom recess will lead to friction between the sheet and the bottom recess. The friction can be expressed as: Where: F f = the friction force [kn] μ f = friction coefficient [-] N = force normal to surface bottom recess [kn] Friction between the concrete lock chamber floor and the rubber sheet can lead to wear and tear of the rubber sheet. The normal force N results from the water pressure in the IRS Lock. Since this pressure is large at the bottom recess, it could be desired to keep the friction factor of the bottom recess small. A material with a small friction factor can be applied in the bottom recess, for instance Teflon or Ultra-High-Molecular-Weight Polyethylene (UHMWPE). It is recommended to do further studies of the sheet behaviour during the deflation and the need for the application of low friction plates in the bottom recess. 92 Master thesis Application of an IRS in a navigation lock

107 13.4 PUMPING EQUIPMENT Air compressors are needed for filling the IRS and compress the air inside the IRS. The choice for the compressors is based on the discharge and the maximum pressure they can deliver. This paragraph will give a first estimation of the amount of compressors needed and the required capacity of the compressors. According to the law of Boyle the volume needed for the compression of a gas under a constant temperature is given by: Where: P 1 = the original pressure in the gas [bar] V 1 = the original volume of the gas [m 3 ] P 2 = the second pressure in the gas [bar] V 2 = the second volume of the gas [m 3 ] T 1 = the temperature in the original gas [ K] T 2 = the temperature in the compressed gas [ K] For a constant temperature the volume of air needed for the inflation of the IRS V 1 becomes: The design of the IRS consists of an internal pressure of 1,17 bar relative to the atmospheric pressure of 1,013 bar (P 1 ). This equals an absolute pressure of 2,183 bar (P 2 ). The total volume of the three IRSs together is 9056 m 3 (V 2 ). This gives a volume of air that is needed for filling the IRS of V 1 = m 3. In case the water in the lock chamber has a lower temperature than the outer air, the water will cool the air in the IRS. Then a larger volume of air is needed. For instance in the case the air is 40 C and the water is 20 C, a volume of m 3 of air is needed. Generally the IRSs will be used during dry periods in the summer. No larger temperature differences than 20 degrees are expected. The time available for the inflation and the deflation of the IRS should follow from economical considerations. Previously in the situation without an IRS an average lock cycle time of 70 minutes for the Eastern Lock has been calculated. On average the lock cycle time consists of two times 15 minutes for levelling operations. Because of the delay for vessels it is preferred that the IRS is inflated as fast as possible. But because of the benefits for saving water, a slightly longer delay for vessels is acceptable. As a first estimation an realistic average time for inflating and deflating the IRS is 15 minutes. When all IRSs are inflated the water level difference Δh air in the lock chamber becomes 1,30 meter. In the past this levelling of 1,30 meter took 3,25 minutes. Therefore, the duration of a full lock cycle with locking in both directions will become two times 11,75 minutes longer. With the previous average filling and emptying time the minimum discharge capacity of the compressors can be calculated. A total volume of V 1 = m 3 needs to be pump into the IRSs in 15 minutes. This leads to a discharge of more or less 22 m 3 /s, which equals m 3 /h. Steffen Woudstra

108 Industrial centrifugal pumps, also called turbo compressors, are available with the discharge and outlet pressure needed for the IRSs. One large compressor can inflate all IRSs at the same time, but also several smaller compressors can inflate the IRSs together. In Table 25 an overview of the volumes and compressor capacity needed per IRS is given. Part lock chamber Volume per IRS (V 2) [m 3 ] Volume of air (V 1) [m 3 ] Discharge capacity needed [m 3 /h] Section A Section B Total for 3 IRSs Table 25 Overview volume and compressor capacity per IRS. The industrial compressors have a range of discharges that lies between a minimum and a maximum discharge. An optimum discharge exists for which the compressor works most efficient. In the IRS Lock it is possible that only section A of the lock chamber is used or only section B. Also in case of maintenance or non-availability of an IRS, it should be possible to inflate a single IRS separately. Because of the desired range of capacities and the range of the compressor capacities the use of three single compressors will be necessary. A suitable standard compressor has been found. This is the Atlas Copco HA9. The properties of this compressor are given in Table 26. Compressor Capacity [m 3 /h] Motor power [kw] Pressure out [bar] Atlas Copco HA to to Table 26 Properties of the Atlas Copco HA9 compressor. An impression of the compressor is given in Figure 91. Additionally, in order to keep the pressure inside the IRS on 1,17 bars, for each IRS also a smaller compressor is needed to induce relatively small adjustments to the internal pressure. Because deformations of the IRS and the use of non return valves in the pumping system, the internal pressure in an IRS will always be fluctuating. The smaller compressor can also be used to apply a small under pressure on the sheet and hence pull the sheet in the bottom recess during the deflated phase. A disadvantage of the large industrial turbo compressors is that they are not made to directly deliver the full capacity. The compressors need time to start up and also the short period of use for the inflation (15 minutes) can lead to inefficient use of energy and a faster deterioration of the compressor. Figure 91 Atlas Copco HA compressor series [L22] Atlas Copco, Oil-free centrifugal compressors HA Series Catalogue, Master thesis Application of an IRS in a navigation lock

109 14 FUNCTIONAL PERFORMANCE In this chapter the functional performance of the designed IRS Lock is considered. The functional performance of the design will result in conclusions related to the technical and economic feasibility of the IRS Lock concept. First the lock cycle time and effectiveness for water saving of the IRS Lock has been determined. After that a RAMS analysis has been performed. With help of the results more insight in the technical feasibility is gained. Thereafter the economics of the IRS Lock have been analyzed by determining the energy use and the Life Cycle Cost of the IRS Lock. The designed IRS Lock has been compared to a water saving solution with a pumping station. In this way the economic competitiveness, and therefore the economic feasibility, has been determined LOCK CYCLE TIME IRS LOCK For the different tidal phases the lock cycle times will be determined. The inflation and deflation of the IRS will lead to additional time needed for the lock operations. It is expected that the IRS only influences the time needed for levelling operations. For the other lock operations an average duration of 40 minutes is used, like was determined in chapter 9. The levelling time varies with the available lift. Previously the time needed for levelling has been described as follows: Where: T levelling1 = the base time needed for levelling: 10 [minutes] T levelling2 = additional time for levelling per meter lift: 2,5 [minutes/meter] z = the available lift [m] The available range of lifts for the different tidal phases is given in Table 27. Tide Minimum lift [m] Maximum [lift] Average -0,16 4,02 Neap 0,37 3,69 Spring -0,54 4,26 Table 27 Minimum and maximum lift for different tides and target water level. In the same way as in chapter 9 mean levelling times are calculated for all lifts and lifts larger than or smaller than 2,5. For lifts of 2,5 meter and larger, the use of the IRS will lead to a mean lock cycle time of 100 minutes. More mean levelling times per tidal phase are given in Table 28. Tide Mean lock cycle time for all lifts normal lock [min] Mean lock cycle time for all lifts in IRS Lock [min] Mean lock cycle time for lifts < 2,5 meter [min] Average 69,6 78,3 65,6 99,8 Neap 70,3 79, ,5 Spring 69,8 78,8 65,25 100,5 Table 28 Mean lock cycle times for locking in both directions. Mean lock cycle time for lifts > 2,5 meter and use IRS [min] Steffen Woudstra

110 14.2 EFFECTIVENESS FOR WATER SAVING During each lock cycle for which the IRSs are used the amount of water that is saved equals the total volume of 9056 m 3 of the three IRSs. It is assumed that the lock chamber is used by the design vessel, therefore the IRSs can only be applied for a minimum lift of 2,5 meter. It is recommended to perform a simulation of shipping in order to approximate a more realistic volume of the water saving and water loss in practice. A simulation will account for a more realistic shipping intensity in time and also for different types of vessels (different draughts). In chapter 9 the water levels in the GTC and WS have been modelled. There the water levels were used to find the optimal height of the IRS. In the model among others the available lift over the IRS Lock is calculated as well as the periods for which the minimum lift of 2,5 meter is present. From the duration of these periods the amount of lock cycles that the IRSs can be used has been calculated. Now the model is used to calculated the total water saving and water loss per tidal period. The tidal fluctuations differ for the mean, spring and neap tide. Per tidal phase the water saving and water loss have been calculated for a tidal period of 24,84 hours. The water levels used for the tides have been previously described in Table 8. For the GTC the target water level as well as the minimum water level are used. Also an imaginary situation where the lift over the Eastern Lock is fixed is analysed in order to say something about the effect of the IRS Lock in different environments. In all calculations continuous locking is assumed. A mean lock cycle time of 70 minutes is used in the calculations in case the IRS is not used. In case the IRS is used, a mean lock cycle time of 100 minutes is applied The target water level in the GTC The target water level in the GTC is +2,13 m NAP. The water loss and water saving have been calculated for this target water level in the GTC combined with the different tidal phases in the WS. The results are shown in Table 29. Amount of lock cycles with a water loss Total water loss per tidal period [m 3 ] Amount of lock cycles with use IRS Total water saving per tidal period [m 3 ] Average tide Neap tide Spring tide Ratio water saving 25% 23% 26% relative to water loss Table 29 Water loss and saving for the target water level in the GTC. The water loss for the neap tide is largest. This is the case because for the neap tide a positive lift is present during the full tidal cycle. Hence, during all lock cycles the GTC has the highest water level and a water loss is present. For the average and spring tide, also negative lifts occur. During the periods with a negative lift, no water is lost from the GTC. 96 Master thesis Application of an IRS in a navigation lock

111 The minimum water level in the GTC The minimum water level in the GTC is +1,88 m NAP. The results for the calculations of the performance of the IRS for the minimum water level are gathered in Table 30. Amount of lock cycles with a water loss Total water loss per tidal period [m 3 ] Amount of lock cycles with use IRS Total water saving per tidal period [m 3 ] Mean tide Neap tide Spring tide Ratio water saving 17% 17% 18% relative to water loss Table 30 Water loss and saving for the minimum water level in the GTC. From the results follows that the IRS Lock is less effective for the minimum water level than for the target water level. This is caused by the smaller available lift, leading to a shorter period and therefore less lock cycles for which the IRS can be used. In practice a water saving is more needed in case water scarcity occurs. In such a situation low water levels are present in the GTC and the need for a water saving is high. When the crest height of the IRS is designed 2,2 meter high instead of 2,5 meter, it is theoretically possible to used the IRS for 6 lock cycles in case of the minimum water level in the GTC. Although the volume inside the IRSs will be a little bit smaller, and so is the lost volume (smaller lift), the ratio of the water saving to the water loss will become almost 30% Imaginary situation with a constant lift A constant lift over the Eastern Lock is assumed. The lift of 2,5 meter equals the height of the IRSs. The length between the low water gates is 290 meter and the width is 24 meter. For a constant lift of 2,5 meter a water loss of m 3 per lock cycle is found. The volume inside the IRSs equals 9056 m 3. Hence, for this imaginary situation the ratio of the water saving relative to the water loss is 52%. A water loss is still present as the IRS is not covering the full length of the lock chamber and the shape of the cross section is curved, see Figure 92. In case the Eastern Lock was not equipped with intermediate gates and one large IRS with a total length of 255 meter was designed, the water saving should be m 3 per lock cycle. This represents a saving of 63% of the total water loss. Theoretically a 100% water saving can be achieve when the IRS has a larger height than the available lift. In order to guarantee the minimum required keel clearance the lock chamber bottom will have to be lowered or only vessels with a small draught can be allowed. From the above follows that the IRS Lock is much more effective in case it is applied to an inland lock were only relatively small water level fluctuations occur. Figure 92 Effectiveness IRS Lock. Areas were water is saved have green shading. Steffen Woudstra

112 14.3 RAMS-ANALYSIS The RAMS-analysis is a tool for determining quality of a (designed) system. The quality is determined based on the four RAMS aspects Reliability, Availability, Maintainability and Safety. A RAMS-analysis can be used for each life cycle phase of the system and for all levels of the analysed system. The RAMS-analysis also serves as an input for system engineering. In order to determine the quality of the designed IRS Lock a RAMS-analysis has been executed. A more extensive description of the RAMS-analysis and the results is presented in Appendix System and method The system IRS Lock studied in this thesis has been described in paragraph 6.3. In the RAMS-analysis the design of the system IRS Lock has been analysed. On subsystem level the RAMS-analysis is limited to the subsystem inflatable rubber structure. In Figure 93 the designed system, subsystem and elements considered in the RAMS-analysis are given. Figure 93 System for RAMS-analysis. The RAMS-analysis had been started before the IRS Lock has been designed. Before the design the desired RAMS-performance was defined and the RAMS-requirements were set. The RAMSrequirements were also used as input for the functional requirements and design goals presented in paragraph 6.4. Also the methods for the verification and assessment of the RAMS-performance were selected. After the design of the IRS Lock, the RAMS-performance of the design has been assessed and the design has been verified. In this master thesis a first design of the IRS Lock was made. For a first design qualitative methods are best suitable for the analysis of the RAMS-performance and the verification of the design. The following methods were used: Methods for the analysis of the RAMS-performance: Failure Mode Effect Analysis (FMEA) Analysis with help of experts. Methods for the verification: Execution of checks. Analysis with help of experts. In case the system did not meet the desired RAMS-performance, the occurring problems had to be corrected in the step where they originated from. Obviously the RAMS-analysis is a cyclic method. 98 Master thesis Application of an IRS in a navigation lock

113 Conclusion RAMS-analysis The performance of the designed system has been assessed with help of a FMEA and the opinion of an expert in the field of navigation locks. Furthermore, the designed system has been verified with help of the expert. The FMEA gives insight in the failure mechanisms of the system. The failure mechanisms with the largest risk are all related to achieving and maintaining the desired pressure inside the IRS. In case the desired pressure inside the IRS is not reached or too large, risk of damage to the IRS occurs. The damage can be among others the result of a too large pressure in the sheet, or collision of a vessel into the sheet. In order to reduce the risk, two parallel systems for the operation of the IRS have been designed. The first is an automatic operating system, the second a manual operation by a human operator. Besides that, mechanical over pressure valves and non return valves have to prevent a too large overpressure or an uncontrollable deflation of the IRS. A redundant system for the compressors and valves results. Conclusions for all RAMS-aspects have been formed with help of the results of the FMEA and the opinion of the experts. Reliability A blowout of the IRS (total failure) could affect the reliability of the lock chamber. A blowout is not likely to happen due to the limited overpressure inside the IRS (up to 0,35 bar). A blowout will be prevented by the application of over pressure valves and a limited compressing capacity of the compressors. More studies to a blowout or large rupture of the rubber sheet are recommended. Availability With the implementation of a new concept like the IRS Lock a lower availability of the lock chamber may be acceptable. The expected non-availability due to the presence of the IRS is one week. One week is likely to be acceptable in practice. A redundant system has been designed in order to keep the non-availability on an acceptable level. Maintainability Planned maintenance can be executed at the same time as maintenance to the lock chamber. In case of maintenance the lock chamber can be pumped dry. Then the IRS is easy to reach. For non-planned maintenance it is expected that the mean time to repair and the duration of the repair or in total maximum two days. Safety The presence of the submerged IRS will not lead to a larger probability of accidents affecting life or health. Based on the results of the RAMS-analysis and verification has been concluded that the designed IRS Lock meets the desired quality. A lot of risk remains and more extensive studies of the risk are needed. The IRS is considered as a subsystem vulnerable for failure, because: The system contains an innovative concept that is essential for the primary function of the IRS. The system contains moving elements, essential for the primary function saving water. The operating system is complex. The system does not have back-up systems for water saving. Because the vulnerability of the subsystem IRS, it is recommended to do a quantitative RAMSanalysis after the design of the IRS Lock is further elaborated. Steffen Woudstra

114 14.4 ENERGY CONSUMPTION Energy is needed for compressing the air and pumping it into the IRS. The energy consumption of the IRS Lock is compared to the energy consumption of an alternative water saving solution with a pumping station. Comparing the energy use of both methods gives insight in the economic competitiveness of the IRS Lock and therefore the economic feasibility Imaginary case for the comparison of energy use An imaginary case is assumed. In the case a lock chamber separates two sections of a waterway with a water level difference Δz of 1 meter. The depth in the lock chamber is 1 meter, which equals the minimum keel clearance in the IRS Lock. The water level in the imaginary lock chamber is equal to the water level of the lower section of the waterway. The situation is schematized in Figure 94. Figure 94 Situation imaginary case. The water loss during levelling without vessels is: Where, for the imaginary case: A = the horizontal cross sectional area of the lock chamber [m 2 ] Δz = the lift over the lock chamber [m] In order to save the lost volume, two methods for levelling are compared: 1) Fill the lock chamber by inflating an IRS with a volume equal to V loss. Emptying will be executed by deflating the IRS. In this way no water loss will occur. 2) Fill the lock chamber by pumping a volume of water equal to V loss from the lower section of the waterway into the lock chamber. Emptying will be executed under free flow towards the lower section. In this way no water loss will occur. The energy needed for both methods is a function of the lift. For a range of lifts the energy needed to safe a unit volume (1 m 3 ) of water will be determined. In a practical situation the water loss is larger than the unit volume and the lift is known. In such a practical situation the energy needed for both methods can easily be found by multiplying the energy needed for saving the unit volume of water times the volume of the total water loss. A description of the energy use by both methods follows from here. 100 Master thesis Application of an IRS in a navigation lock

115 Energy needed for levelling with an IRS (method 1). The energy needed to compress a gas, like air, is given by the work done by the gas. Energy is linked to pressure by the ideal gas law (law by Boyle and Gay-Lussac), which expresses pressure in terms of volume: Where: p = the pressure [bar] n = the amount of air: 44,63 [mol] R = gas constant for air: 8, [J/(molK] T = the absolute temperature [K] V = volume [m 3 ] When is assumed that the changes in temperature are small and heat exchange with the surrounding water is easy, the process of compressing the air in the IRS is by approximation isotherm. In an isothermal process a system changes while the temperature remains constant. For an isothermal process use can be made of the following formula describing the energy needed for changing the pressure in a gas (found by putting the pressure P in the work integral): Where: P 1 = the outer air pressure [bar] P 2 = the internal air pressure [bar] For air, the value of T = 283 K (equal to 10 C) and P 1 = 1,013 bar are common. The sheet of the IRS is connected to the lock chamber bottom. The internal pressure in the IRS has to be at least equal to the water pressure at the bottom of the lock chamber. During the inflated phase this water pressure is formed by the 1 meter of water plus the height Δz of the lift. For the imaginary case the internal pressure can be described as a function of the lift: Where: d = the depth in the lock chamber for the lower water level: 1,0 [m] Δz = the lift over the lock chamber [m] ρ = mass density of the water: 1025 [kg/m 3 ] The factor 0,01 accounts for the fact that 1 kpa equals 0,01 bar. Now also the work done to compress a gas can be described as a function of the lift. The energy needed per unit of saved volume of water as a function of the lift is plotted in Figure 95. Steffen Woudstra

116 Energy needed for levelling by pumping (method 2). The energy needed to executed levelling by pumping will be calculated. The lock chamber of the imaginary case is filled by pumping water from the lower section of the waterway into the lock chamber. The energy needed for this process can also be calculated as a function of the lift. The energy needed to bring a mass to a higher level is called potential energy. In formula form the potential energy is described as: Where: m = the mass of an object or in this case the water volume [kg] g = the acceleration by gravity [m/s 2 ] h = the height [m] When a lift Δz is present, the average height to which the water has to be pumped is half the lift (0,5*Δz). Hence, the potential energy for filling the lock chamber by pumping is described by: Now the potential energy needed for pumping is also plotted as a function of the lift in Figure 95. Figure 95 Energy needed for levelling by both methods. 102 Master thesis Application of an IRS in a navigation lock

117 Analysis of the results for energy use From the results it is obvious that until a lift of 30 meter pumping is less energy consuming. For a lift of 31 meter and higher, compressing air in the IRS is less energy consuming. For a lift of 31 meter the water pressure at the bottom is the result of 32 meter water depth and the atmospheric pressure, which equals in total 4,2 bar. In order to compress the air inside the IRS to minimally 4,2 bar, a volume of air of almost 4,2 times the internal volume of the IRS is needed. It will require a large compressor capacity in order to keep the lock cycle time limited. Besides that, a really large and strong rubber sheet is needed to achieve a height of the IRS similar to the lift. The membrane force will be really large as a result of the overpressure along the sheet. The strength of the rubber sheets in practice is limited. Other water saving concepts are available for locks with a large lift, for instance water saving basins. In reality the use of the IRS will be even more energy demanding due to the fact that in practice the depth in a lock chamber will be larger than only the keel clearance (an additional depth is needed for the draught of vessels). Therefore a larger internal pressure in the IRS is needed, leading to a larger energy demand by the compressors. The blue graph in Figure 95 will shift and will make the situation for the use of the IRS worse. So far, it has been assumed that the full water loss had to be saved. When only part of the water loss has to be saved, the situation is even more beneficial for the method with pumps. In such a situation the water only has to be pumped up to a limited height smaller than the total lift. This leads to an energy use per unit of saved volume that is smaller than determined before. Counter to the method with pumping, the internal pressure in the IRS always has to be at least equal to the water pressure at the lock chamber bottom for the full depth in the lock chamber. Losses in the system have to be taken into account in the comparison. In general the efficiency of air and water pumps do not differ a lot but water pumps are generally more efficient. The efficiency of the pumps depends on several factors, for instance the discharge. As an indication an efficiency of a pump in a pumping station up to 0,8 is possible. From the above it is obvious that based on only the energy use pumping is a better alternative for saving water up to lifts of at least 30 meter. In case of larger lifts, technical limitations for the strength of the sheet make the use of an IRS with a crest height similar to the lift unfeasible. Steffen Woudstra

118 14.5 LIFE CYCLE COST The cost of the IRS Lock will be determined for the total life cycle of the IRS Lock. Only the costs due to the application of the IRS are taken into account. Usual cost of the lock structure which also should be present without the application of the IRS are not taken into account. The total life cycle of the IRS consists of four phases. These phases are the design, construction, lifetime and demolition phase. The total cost of saving a certain volume of water with the IRS Lock will be compared to the cost of saving the same volume of water with a general pumping station Inventory cost An inventory of the cost has been made for an IRS Lock with the same dimensions as the Eastern Lock in Terneuzen. It is assumed that a complete new IRS Lock will be build. Only the cost caused by the existence of the IRS are taken into account. Per phase the most important posts have been inventoried. The cost of the most important posts have been estimated with help of the cost of reference projects and cost codes 23. In the cost codes the cost of materials, labour, equipment and more are given. Based on the specific cost codes an estimation for the costs per post is made. With help of the experience of a specialist the determined costs are revised. The posts and the expected costs per post are more extensively described in Appendix 11. It is expected that deviations from the expected cost of 40% are possible in practice. The final result for the cost estimation for the total life cycle of the IRS Lock are gathered in tables. The Net Present Value (NPV) of the future cost have been determined with a discount rate of 2%. In Table 31 an overview of the cost of the IRS in section A of the lock chamber is given. The results per IRS for section B are given in Table 32. Design Construction Lifetime Demolition Total life cycle Duration [years] Cost per year , , , , ,- Total cost , , , , ,- NPV total cost , , , , ,- Table 31 Overview Life Cycle Cost IRS section A. Design Construction Lifetime Demolition Total life cycle Duration [years] Cost per year , , , , ,- Total cost , , , , ,- NPV total cost , , , , ,- Table 32 Overview Life Cycle Cost per IRS for section B. It should be kept in mind that in section B two IRSs will be build. The costs are given for only one IRS. The lifetime phase is by far the most costly phase in the life cycle of the IRS Lock. The above costs have been determined for a lifetime of the rubber sheet of two years. This means that each two years a complete sheet renewal is needed. For section A the rubber sheet will cost ,- and for section B the sheet will cost ,-. More or less 55% of the total life cycle costs consists of 23 [W5] GWW kosten, Master thesis Application of an IRS in a navigation lock

119 the cost of the sheet renewal. As the lifetime of the sheet is hard to estimate, it is recommended to do more studies of the lifetime of the sheet. Also improving the quality of the sheet can be beneficial for the life cycle cost. Different scenarios for the lifetime of the sheet have been calculated. The total life cycle cost of the three IRSs (like before for a lifetime of 20 years) have been determined for a sheet lifetime of 1, 2 and 5 years. The results are given in Table 33. Lifetime sheet [years] Total cost IRSs NPV total cost IRSs (2%) , , , , , ,- Table 33 Total LCC IRSs for different lifetimes of the rubber sheet Cost alternative water saving solution: pumping station With the three IRSs per lock cycle a volume of 9056 m 3 is saved. In the Eastern Lock the IRSs can be used for maximum 6 lock cycles per tidal period of 24,84 hours. This will give a total water saving of m 3 per tidal period. Continuous pumping during the full tidal period with a discharge of 2264 m 3 /h, or more or less 40 m 3 /min, would lead to the same water saving. Such a discharge capacity is common for small polder pumping stations. Under normal tidal conditions the pumping station needs to be able to enlarge the water head by maximum 4,5 meter. In practice it should be beneficial to pump with a larger discharge when the lift over the lock chamber is small. But this advantage will not be taken into account here. With the previous requirements the cost of a reference pumping station is selected. Cost codes for pumping stations give a wide range of cost of 3.000,- m 3 /min up to ,- m 3 /min. When ,- m 3 /min is used for the situation of the Eastern Lock, this would lead to a pumping station with design and construction cost of ,-. These pumping station do have a least a lifetime of 20 years. Obviously the design and construction cost of the IRS in the IRS Lock are much higher. Considering the cost of use, previously it was concluded that a pumping station is more energy efficient than the IRS Lock. The cost of energy do only have a small contribution to the cost of the use of the IRS Lock. Also the following cost of use are present in the IRS Lock: The cost of the sheet renewal each two years. The cost of additional delay for vessels because of the longer lock cycle time. The cost of the downtime of the lock chamber caused by the presence of the IRS. Extensive inspections, monitoring and tests of the rubber sheet. Maintenance and repairs. A pumping station is build parallel to the lock chamber. It is obvious that the first three of the above cost post will not be present in case of saving water with a pumping station. Inspection, monitoring and tests, maintenance and repairs are more easy to executed for a parallel pumping station than for the IRS inside the lock chamber. In case of inspections or maintenance the availability of the lock chamber is not affected by the presence of the pumping station. Comparing the above cost factors it may be obvious that saving water with the IRS Lock will be much more expensive than saving the same amount of water with a pumping station. Steffen Woudstra

120 15 CONCLUSIONS AND RECOMMENDATIONS In this chapter the final conclusions of the thesis study are presented. Also, recommendations for future studies on IRSs and the IRS Lock are given CONCLUSIONS The conclusions are separately presented for the design and its performance, the technical and economic feasibility. Design of the IRS Lock and its performance In this thesis, an innovative IRS Lock was designed. The design combines simplicity with a relatively large water saving. Due to the small overlength of the sheet the vertical reach of the sheet is relatively small. This is beneficial for the available keel clearance in the lock chamber. The bottom recess provides space for the storage of the rubber sheet. Because of the small overlength and simple bottom recess it is expected that the duration of the inflation and deflation of the IRS takes no longer than 15 minutes each. The Eastern Lock in Terneuzen is used as a case environment. Three IRSs have been designed in the lock chamber. An overview of the design is presented in Figure 96. The IRSs are shown in red. Figure 96 Overview final design IRS Lock. Per lock cycle the three IRSs together will save 9056 m 3 of water. Because of the tidal fluctuations in the water level of the Western Scheldt, and therefore the limitations in available depth and keel clearance, the IRS can only be used during 6 of the 18 lock cycles per tidal period. Therefore the total amount of water saved per tidal period will be m 3. This represents a water saving of 25% of the total water loss during a normal tide. In case the Eastern Lock would be located in a situation without tides, the water saving would be 52%. It is possible to design alternative solutions for the IRS Lock which are more effective for water saving. In these solutions a larger effectiveness is the result of deepening the lock chamber and applying IRSs with a larger crest height. The counter side is that these designs will perform worse in practise because of the increasing complexity and life cycle cost. 106 Master thesis Application of an IRS in a navigation lock

121 Technical feasibility The technical feasibility largely depends on the geometry and strength of the rubber sheet of an IRS. The strength of the rubber sheets is limited. The IRSs have been designed in such a way that no large stress concentrations occur in the sheet due to discontinuities. The membrane force in the midsection is 1250 kn/m in warp direction for a situation with the hydrostatic pressure as the only external load. The strength of the sheet has been verified with safety factors. Load factors were used to take the different load situations into account. In warp direction and longitudinal direction strengths of 2925 kn/m and 1463 kn/m respectively are required. A deepened bottom recess has been designed that accommodates space for the storage of the sheet during the deflated phase. The hydrostatic pressure in the lock chamber is expected to force the sheet into the bottom recess. A safe minimum keel clearance of 1 meter above the highest point of the IRS is guaranteed during all phases of use. From the FMEA it follows that most failure mechanisms and the failure mechanisms with the largest risk are related to managing the pressure inside the IRS. The pressure inside the IRSs will be managed with help of regular turbo compressors. Regular conduits and valves are used to guide air in and out of the IRSs. Additional measures are taken in order to create a redundant system and keep the risk of the designed IRS Lock at an acceptable level. Based on the first design and its performance it is concluded that the IRS Lock is technically feasible. Economic feasibility The benefit of saving a unit volume of water depends on the scarcity of water. For general situations, the costs for the IRS Lock concept are compared to the costs for an alternative water saving solution. As an alternative for the IRS Lock, a regular pumping station can be build next to the lock chamber. Such a pumping station also has the advantage of not occupying a lot of space. The LCC of the IRS Lock have been determined for a lifetime of 20 years. The total costs are expected to be 124 million (NPV, 2% discount rate). The largest component of the LCC is formed by the renewal of the rubber sheet. This component represents 55% of the total LCC. It is expected that the sheet has to be renewed each two years, because of the high frequency of inflations and deflations. This high frequency of inflating and deflating is expected to lead to a fast deterioration of the rubber sheet. In case the quality of the sheet is improved and the lifetime of the sheet becomes 5 years, the total life cycle costs are expected to be 70 million. Other important cost components of an IRS Lock that are not present in case of a conventional navigation lock are the result of: 1) An increase of 23,5 minutes of the average lock cycle time, leading to an additional delay for vessels and a lower capacity of the Eastern Lock. 2) The additional downtime of the lock chamber caused by failure and maintenance of the IRS. 3) Extensive inspections, monitoring and tests of the rubber sheet. Because of the limited experience with submerged IRSs, the cost of the design, construction and risks will be significant as well. The second and third of the above described cost components will not occur for a parallel pumping station. In addition, the design and construction costs of regular parallel pumping stations are much smaller than for the IRS Lock. Besides, saving a unit volume of water with a pumping station requires less energy than saving the same unit volume with an IRS. Comparing the costs of an IRS Lock with the costs of a lock equipped with a pumping station, it is concluded that the IRS Lock is less competitive. Steffen Woudstra

122 15.2 RECOMMENDATIONS The previous conclusions are obtained based on the first design of the IRS Lock. For future research related to the IRS Lock concept or other inflatable rubber structures it is advised to regard the following recommendations. 1) The shape and behaviour of the submerged rubber sheet during the inflation and deflation comes with a lot of unknowns. The time needed for the inflation and deflation is estimated, but has to be verified with help of scale tests. 2) The lifetime of specific rubber sheets is hard to determine without testing the actual sheet. The influence of a high frequency of inflations and deflations on the deterioration and lifetime of the rubber sheet is hard to estimate. Also knowledge related to the effect of cyclic loads and ageing on the lifetime of the sheet is limited. A sheet renewal leads to large cost. It is recommended to execute more studies related to the lifetime of the rubber sheet. 3) It is recommended to perform a 3D analysis of the stresses occurring in the rubber sheet. From the 3D analysis more can be learnt about stress concentrations in the sheet and deformations of the sheet. This information is of use during the verification of the strength of the sheet. 4) It is recommended to perform a simulation of shipping in order to approximate the volume of the water saving and the water loss in practice. A simulation will account for a more realistic shipping intensity in time and also for different types of vessels. For vessels with a small draught compared to the design vessel, the IRSs can be used for lifts smaller than 2,5 meter. Besides that the use of only the IRS in section A or only the IRSs in section B of the designed IRS Lock can be incorporated. 5) Elongation of the rubber sheet in time is important for the shape of the IRS (and in this case the available keel clearance). The elongation of the rubber sheet should be taken into account in later studies of the IRS Lock. 6) Out of the RAMS-analysis is found that the IRSs are vulnerable to failure. Therefore it is recommended to perform a quantitative analysis of the RAMS-performance and a quantitative verification of the design. 7) The deflation of the IRS and the distribution of the sheet over the bottom recess needs further studies. Scale tests have to give more insight in how the sheet is distributed over the bottom recess. Additionally, the need of the application of low friction plates in the bottom recess has to be determined. 8) In this thesis the filling and emptying of the IRS with air is assumed to be executed serial to filling and emptying of the lock chamber with water. The lock cycle time can be reduced if the filling and emptying with both air and water is executed parallel to each other. More studies of the loads during filling and emptying are needed in order to determine if parallel levelling operations are possible. 9) The use of reinforcement fabrics with a larger stiffness than Nylon needs more research. With stiffer reinforcement fabrics the strength of the rubber sheets can be enlarged. Hence, the IRS can also be applied in larger and deeper locks. Also the use of different kinds of reinforcement fabrics in different parts of the structure needs more studies. The use of Nylon in the ends and Kevlar in the midsection can lead to a more efficient design. 108 Master thesis Application of an IRS in a navigation lock

123 REFERENCES Literature [L1] W.F. Molenaar and others, Hydraulic Structures Locks, March [L2] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 1, [L3] PIANC, Final Report of the International Commission for the Study of Locks, [L4] ACP (Autoridade Del Canal De Panama), Study of additional combinations of locks water saving basins for proposed post-panamax locks at the Panama Canal. [L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics, Hydraulische Aspecten van balgstuwen en balgkeringen, december [L6] Bouwdienst Rijkswaterstaat, Kennis- en Ervaringsdocument Balgkering Ramspol, December [L7] R.D. Parbery, A continuous method of analysis for the inflatable dam, [L8] P. Versteegt, Balgsluis Eefde, 2011 [L9] Hollandsche Beton- en Waterbouw, Storm surge barrier Ramspol, 1999 [L10] M. van Breukelen, Improvement and scale enlargement of the inflatable rubber barrier concept, December [L11] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 2, [L12] Ir. G.J. Schiereck, Bed, bank and shore protection, [L13] PIANC, Innovations in navigation lock design n , [L14] Rijkswaterstaat, Vaarwegkenmerken in Nederland, February [L15] Rijkswaterstaat, Waternormalen, [L16] VNSC (Vlaams-Nederlandse Scheldecommissie), Zoutgehalte, waterstand KGTB en debiet KGT , [L17] J. Dorreman, Balgstuwen gevuld met lucht en/of water, May [L18] A. Dirkmaat, Balgkering het Spui, August [L19] HBW, Detailontwerpnota Nylon Balgdoek, February [L20] Rijkswaterstaat directie Zeeland, Scheepvaart in Zeeland 2008, July [21] HBW, Detailontwerpnota Nylon Balgdoek Bijlage B, February [L22] Atlas Copco, Oil-free centrifugal compressors HA Series Catalogue, Steffen Woudstra

124 [L23] Rijkswaterstaat Dienst Verkeer en Scheepvaart, Richtlijnen Vaarwegen 2011, December 2012 [L24] Nederlandse Adviesdienst Verkeer en Vervoer, Rapport verkeersgegevens sluis Terneuzen, March Websites [W1] [W2] [W3] Google, [W4] GWW kosten, Master thesis Application of an IRS in a navigation lock

125 LIST OF FIGURES Figure 1 Impression of the cross section of the design 'sheet connected to the walls'.... V Figure 2 Overview of the IRS Lock concept. The inflatable rubber structure is shown in yellow Figure 3 Traditional navigation lock in Terneuzen ([W1] 3 Figure 4 Lay-out of a navigation lock ([L1] W.F. Molenaar and others) Figure 5 Overview components of the keel clearance ([L2] Rijkswaterstaat) Figure 6 Water loss during locking cycle([l1] W.F. Molenaar and others) Figure 7 Top view of a twin lock ([L3] PIANC) Figure 8 Method water saving basins ([L4] Panama Canal Authority) Figure 9 Overview Hohenwarthe navigation lock ([W2] 8 Figure 10 Inflatable weir ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics) Figure 11 The Ramspol barrier during the construction, deflated on the left and inflated on the right ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics) Figure 12 One-sided clamped IRS dam Figure 13 Global equilibrium inflatable weir ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics) Figure 14 Ramspol barrier during the inflated state ([L6] Bouwdienst Rijkswaterstaat) Figure 15 Cross section Ramspol barrier ([L6] Bouwdienst Rijkswaterstaat) Figure 16 Pressure and weight acting on a cylindrical IRS ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics) Figure 17 Loads on a rubber element ([L7] Parbery) Figure 18 Normal forces in a double curved membrane loaded by an internal overpressure Figure 19 Example IRS for the explanation of the equilibrium in an IRS Figure 20 Force distribution in example IRS Figure 21 Pressure situation for a submerged air filled IRS Figure 22 Pressure situation during deflation pushing IRS together leading to a larger height Figure 23 Scale model P. Versteegt ([L8] P. Versteegt) Figure 24 Inflation of the scale model ([L8] P. Versteegt) Figure 25 Deflation of the scale model ([L8] P. Versteegt) Figure 26 Composition rubber sheet Ramspol barrier ((L6] Bouwdienst Rijkswaterstaat) Figure 27 Overview bottom recess Ramspol barrier ([L5] Ministerie van infrastructuur en milieu, WL Delft Hydraulics) Figure 28 Flow pushes the rubber sheet downstream ([L9] Hollandsche Beton- en Waterbouw) Figure 29 Desired distribution sheet in bottom recess ([L9] Hollandsche Beton- en Waterbouw) Figure 30 Flap after test closure Ramspol barrier ([L9] Hollandsche Beton- en Waterbouw) Figure 31 Jet flow behind an opening due to levelling ([L11] Bouwdienst Rijkswaterstaat) Figure 32 Wave of translation after opening a lift gate ([L11] Bouwdienst Rijkswaterstaat) Figure 33 Flow phenomena around a sailing vessel ([L13] Ir. G.J. Schiereck) Figure 34 Situation Eefde lock complex ([W3] Google) Figure 35 Pumped volume by the pumping station of the Eefde lock Figure 36 Levelling procedure with IRS for vessel sailing upstream Figure 37 Levelling procedure with IRS for vessel sailing downstream Figure 38 Diagram lock operations and phases of use IRS ( [L13] PIANC (slightly adjusted) Steffen Woudstra

126 Figure 39 Functional decomposition of the macro-system waterway Figure 40 Explanation width of the sheet (L) and width between clamp lines (B) Figure 41 Aerial view of the situation around the Terneuzen Lock complex ([W3] Google) Figure 42 Aerial view of the Terneuzen Lock complex and Eastern Lock ([W3] Google) Figure 43 Overview dimensions Eastern Lock Figure 44 Levels bottoms and sills Eastern Lock Figure 45 Water levels for the GTC and the WS scaled in the cross section of the Eastern Lock Figure 46 Impression of the zero solution of the IRS Lock Figure 47 Impression alternative 1: Rubber sheet connected to the walls Figure 48 Impression alternative 2: Rectangular shaped structure Figure 49 Impression alternative 3: Rubber structure controlled by cables Figure 50 Impression alternative 4: Perforated floor Figure 51 Impression alternative 5: Flaps acting as side plates Figure 52 Explanation used terms for the water loss and saved volume by the IRS Figure 53 Water levels for an average tide in the WS and target water level in the GTC Figure 54 Available lift in time. During the periods P min,lift a minimum lift of 2,5 meter is available Figure 55 First estimate saved volume per tidal cycle as a function of the height of the IRS Figure 56 Equilibrium in an element according to Dorreman Figure 57 Schematization iterative process for finding the 2D static equilibrium Figure 58 Shape of the sheet for the Eastern Lock Figure 59 Overpressure along the sheet in the Eastern Lock Figure 60 Impression loads by moving vessels acting on deflated IRS Figure 61 Jet flow through openings by levelling operations acting on deflated IRS Figure 62 Explanation of the dimensions of the bottom recess Figure 63 Shape of the sheet for a connection height of 0,55 meter Figure 64 Overview of the selected alternative Figure 65 Dimensions of the ends of the IRS Figure 66 Overview of the different sections of the IRS and the clamp line (in red) Figure 67 Total design of the two smaller IRSs for the Eastern Lock Figure 68 3D impression of the IRS for section B of the Eastern Lock Figure 69 End configurations with parallel rubber strips (top view) Figure 70 Top view of the IRS composed of rubber strips (inflated phase) Figure 71 Layout of the flat sheet (black contour) and clamp line (red contour) Figure 72 Layout sheet and clamp line Ramspol barrier Figure 73 Overview of the dimensions of the Eastern Lock Figure 74 Layout Eastern Lock with three IRSs (red contours) Figure 75 Vertical reach of the sheet for check keel clearance Figure 76 Minimum available depth for each phase of use Figure 77 Overview total design IRS Lock Figure 78 Available keel clearance for design vessel with draught of 4,3 meter Figure 79 Sheet design IRS Lock Figure 80 Teeth clamp ([L21] HBW) Figure 81 Detail application traditional clamp connection in IRS Lock Figure 82 IRS Lock with horizontal clamp line Figure 83 Connection with a hinge Master thesis Application of an IRS in a navigation lock

127 Figure 84 Layout of the flat sheet (black contour) and clamp line (red contour) Figure 85 Overview bottom recess midsection Figure 86 Bottom recess and sheet at midsection Figure 87 Detail corner bottom recess midsection Figure 88 Design bottom recess (blue), clamp line (red) and sheet (black) at the end Figure 89 Overview longitudinal cross section IRS Figure 90 Total layout bottom recess (blue) and clamp line (red contour) Figure 91 Atlas Copco HA compressor series Figure 92 Effectiveness IRS Lock. Areas were water is saved have green shading Figure 93 System for RAMS-analysis Figure 94 Situation imaginary case Figure 95 Energy needed for levelling by both methods Figure 96 Overview final design IRS Lock Steffen Woudstra

128 LIST OF TABLES Table 1 Strength properties of reinforcement fabrics ((L6] Bouwdienst Rijkswaterstaat) Table 2 Properties rubber sheet Ramspol Barrier (L6] Bouwdienst Rijkswaterstaat) Table 3 Feasibility potential for the four case situations Table 4 Inner dimensions lock chambers Terneuzen lock complex Table 5 Maximum vessel dimensions Eastern Lock Table 6 Features of the Eastern Lock Table 7 Hydraulic boundary conditions in Gent-Terneuzen Canal Table 8 Tidal water levels in the Western Scheldt at Terneuzen Table 9 Determination of relative importance of the criteria Table 10 Assessment of alternatives for each criterion Table 11 Water levels in the GTC during use of the IRS Table 12 Equilibrium input for the Eastern Lock Table 13 Presence of hydraulic loads per phase of use of the IRS Table 14 Hydrostatic pressure acting on the IRS during the inflated state Table 15 Hydrostatic pressure acting on the IRS during the deflated phase Table 16 Results from calculations jet flow by levelling operations Table 17 Flows by moving vessels acting a load on the IRS Table 18 Input for equilibrium Eastern Lock for connection height of 0,55 meter Table 19 Length of the IRSs and sheets Table 20 Longitudinal dimensions IRS in section B Table 21 Longitudinal dimensions IRS in section B Table 22 Representative load for the strength check Table 23 Summary values factors in safety checks Table 24 Qualitative consideration of the lifetime of the sheet for the IRS Lock Table 25 Overview volume and compressor capacity per IRS Table 26 Properties of the Atlas Copco HA9 compressor Table 27 Minimum and maximum lift for different tides and target water level Table 28 Mean lock cycle times for locking in both directions Table 29 Water loss and saving for the target water level in the GTC Table 30 Water loss and saving for the minimum water level in the GTC Table 31 Overview Life Cycle Cost IRS section A Table 32 Overview Life Cycle Cost per IRS for section B Table 33 Total LCC IRSs for different lifetimes of the rubber sheet Master thesis Application of an IRS in a navigation lock

129 Appendices Design and feasibility study for the application of an inflatable rubber structure in a navigation lock. Author: S.D. Woudstra Assessment Committee: Prof. dr. ir. S.N. Jonkman Ir. W.F. Molenaar Ir. S. Pasterkamp Ing. D.H.M. Adriaansens Document: Appendices Master of Science Thesis report Date: Steffen Woudstra

130 Content Appendices Appendix 1 Field with unknowns for further research A1.1 Technical feasibility A1.2 Economic feasibility Appendix 2 Case selection process A2.1 Qualitative consideration of case alternatives A2.2 Selection of a case from practice A2.3 Description of the Terneuzen Lock complex Appendix 3 Shape and equilibrium IRS in Large Sea Lock A3.1 Layout and dimensions Large Sea Lock A3.2 2D static equilibrium IRS in Large Sea Lock Appendix 4 Assessment alternatives Multi Criteria Analysis A4.1 Alternatives A4.2 Explanation of assessment MCA criteria Appendix 5 Calculations for the height of the optimal IRS Appendix 6 Selection filler medium Appendix 7 Calculation hydraulic loads acting on the IRS A7.1 Hydrostatic pressure A7.2 Loads caused by lock operations A7.3 External loads A7.4 Loads by ship movements A7.5 Conclusion governing loads Appendix 8 Alternatives layout ends of the IRS Appendix 9 Vertical reach of the rubber sheet Appendix 10 Improvements of the sheet Appendix 11 Estimation life cycle cost Appendix 12 RAMS-analysis A12.1 Definitions A12.2 System A12.3 Method A12.4 Results Appendix 13 Failure Mode Effect Analysis List of figures appendices List of tables appendices Master thesis Application of an IRS in a navigation lock

131 Appendix 1 FIELD WITH UNKNOWNS FOR FURTHER RESEARCH During the literature study a wide range of information related to navigation locks and IRSs has been studied. Out of the literature study it is clear a lot of aspects of IRSs are case specific and need more research for the case of the IRS Lock. Besides, experiences with existing IRSs show that there is a lot of space for improvements. As a result of the literature study, the fields with unknowns related to the IRS Lock are given in here. Initially, the literature study started with the question if the IRS Lock concept is feasible. The feasibility is subdivided in two parts, the economic feasibility and technical feasibility. The field with unknowns are subdivided in categories belonging to the economic or technical feasibility. Finally thirteen fields with topics for further research are given in the most right column of the scheme below. A description of the topics is given in this chapter. 1) Filler medium A1.1.1 Structural design 2) Fibre reinforcement 3) Design formula A1.1.2 Structural behaviour 4) Load transfer 5) Specific loads or behaviour A1.1 Technical 6) Equipment A1.1.3 Inflating and deflating 7) Controlling inflating/deflating 8) Energy regeneration/storage A1.1.4 Lifetime 9) Fatigue and ageing Feasibility 10) Robustness 11) Lock cycle time A1.2 Economical A1.2.1 Life cycle cost 12) Cost components 13) Optimal boundary conditions Steffen Woudstra

132 A1.1 TECHNICAL FEASIBILITY A1.1.1 Structural design 1) Filler medium Different fillers have been used for IRSs. The filler medium influences the structural properties and the behaviour of the rubber structure. The filler medium also effects the way the rubber structure behaves during inflation and deflation, and therefore the time needed for the inflation and deflation. 2) Fibre reinforcement Anisotropic properties of a fibre reinforcement can be used to design a rubber structure with an effective force transfer of the loads to the foundation. The new load cases in the IRS Lock will potentially result in a different fibre orientation, load transfer to the foundation, and different distribution of the stiffness. 3) Design formula At present, no design formulae are available for the IRS Lock. Existing design formula for rubber structures are only applicable to specific cases and determined with scale tests. A new design formula for the IRS Lock has to be determined. A1.1.2 Structural behaviour 4) Load transfer 3D numerical models are needed to get information about the load transfer and stresses in the rubber sheet. In the past numerical models have been developed for specific IRSs. In case of the IRS Lock the IRS will not have abutments and will have a different geometry. Numerical modelling of IRSs is complex, since structural properties have to be related to fluid mechanical problems. Besides modelling of the filler medium, modelling of the large deformations and complex geometries of the rubber structure are making 3D modelling hard. 5) Specific loads or behaviour The behaviour of an IRS under general loads in a navigation lock is at the moment unknown. Specific load case for the IRS Lock need further studies. As an example, for a design of the IRS Lock an analysis could be done for jet flow from a vessels main propeller. A1.1.3 Inflating and deflating 6) Equipment An analysis of the equipment needed for filling and emptying the rubber structure in a controlled way is needed. A design of the system of pumps, conduits and valves has to be made. A complete design of the filling and emptying installations and structures will result. 7) Controlling filling and emptying In existing large IRSs, a stable storage of the rubber sheet in deflated phase is not guaranteed. In a lock chamber vessels should not be hit by the rubber sheet during the inflation or deflation. Especially in the case of an air filled rubber structure in a navigation lock, solutions should be found for problems with vacuum and rubber sheets being pushed together by the water pressure. 118 Master thesis Application of an IRS in a navigation lock

133 8) Energy regeneration or energy storage Energy can be regenerated from water or air flow occurring during emptying of the IRS. Energy can also be stored as pressure. In case of an IRS Lock, the air pressure from the rubber structure can be stored with the help of pressure tanks or Gravity Power. In the concept of Gravity Power a heavy piston is lifted by a hydraulic head or air pressure. Energy regeneration or storage can result in a saving of costs and can in this way positively influence the feasibility of the IRS Lock. A1.1.4 Lifetime 9) Fatigue and ageing The lifetime of fibre reinforced rubbers made for specific structures and boundary conditions is hard to predict. The exact composition of the material of the rubber sheet of the Ramspol barrier is kept secret by the producer, who only guarantees the structural properties of the rubber. The amount of inflating and deflating operations in an IRS Lock will largely exceed the amount of inflating and deflating operations for existing IRSs. It is unknown in what extend the repeating filling and emptying operations and the boundary conditions in a navigation lock will influence the lifetime of the rubber and if fatigue will lead to structural damage. 10) Robustness of the rubber sheet The availability of the IRS should be of a certain level. The robustness of the IRS has to be of a certain level to guarantee the availability of the structure. The robustness and material composition of the rubber sheet can be studied. A1.2 ECONOMIC FEASIBILITY A1.2.1 Life cycle cost 11) Lock cycle time It is questionable how fast a rubber structure can be inflated or deflated in a controlled way. The time needed for inflating and deflating directly influences the lock cycle time (serial process). More research is needed to find out how much time a locking cycle will take and if the lock cycle time results in a larger or shorter delay for vessels. 12) Cost components For the economic feasibility it is important to keep the cost as small as possible. Knowledge of the cost components and their influence in the total cost is an important base for decisions on investments. From an analysis of the life cycle cost the cost components should become clear. 13) Economically optimal boundary conditions for IRS Lock For a certain combination of boundary conditions an IRS Lock is most economic. Also the technical feasibility is influenced by the boundary conditions. At present, it is unknown in what boundary conditions the ratio between cost and benefits is optimal. Steffen Woudstra

134 Appendix 2 CASE SELECTION PROCESS In this appendix the selection process and the selected case are more extensively described. A2.1 QUALITATIVE CONSIDERATION OF CASE ALTERNATIVES The feasibility of the IRS Lock concept is influenced by several factors related to different case environments. From first insights the five most important factors are: 1) The location of the lock: inland or coastal 2) Types of the vessels using the lock: commercial or recreation 3) Intensity navigation and distribution of the intensity in time 4) Dimensions and lift 5) Life cycle cost The third until the fifth influence factor are strongly related to the first two influence factors. Hence, the first two influence factors are of the greatest importance. Four general case situations are created by a combination of the first two influence factors: Inland commercial lock Inland recreational lock Coastal commercial lock Coastal recreational lock The way the factors influence the feasibility of the IRS Lock is described below. 1) Inland or sea lock In normal inland locks the only benefit of an IRS Lock is the reduction of the water loss. In sea locks, the IRS Lock could have additional benefits for reducing the salt intrusion. 2) Type of vessels The type of vessels result in a norm for the waiting time and therefore the available time for the inflation and deflation of the IRS. Furthermore, the type of vessels determines the minimum availability required for the lock. The availability requirement depends on economic considerations. It should be noted that specific situations ask for specific norms. With the implementation of a new concept like the IRS Lock longer waiting times and a smaller availability may be acceptable. 3) Intensity navigation and distribution of the intensity in time When the shipping intensity is really small, the average total waiting time is small and more time is available for inflating and deflating the rubber structure. The distribution of the intensity in time is another influence factor affecting the feasibility. In The Netherlands water saving is normally only needed during long dry periods, occurring most often during the summer time. 4) Dimensions and lift Controlling inflation and deflation of small IRSs seems less hard than controlling larger IRSs. For small locks, the water loss is small and it is questionable if measures for water saving are needed. 5) Life Cycle Cost The total life cycle cost (LCC) should be competitive for the LCC for alternative water saving concepts. 120 Master thesis Application of an IRS in a navigation lock

135 The potential cases are further described. Common dimensions and lifts of the potential case situations are given. These numbers are determined with the help and experience of a specialist. The four case situations are compared to each other qualitatively with help of several aspects. The aspects are the availability and waiting times, shipping intensity and distribution of the intensity in time, the water saving potential, the potential for a reduction of salt intrusion and the expected cost and benefits. A2.1.1 Inland commercial lock Inland commercial lock Availability and waiting times Strict, depending on economics. Intensity and distribution intensity Day and night, all year long Dimension 125 by 12 m Lift 0 to 3,5 m Water saving Large water saving Salt intrusion No Cost, total benefits High costs, average benefits Table A 1 Qualitative assessment feasibility potential inland commercial locks. The high navigation intensity and large requirements for the availability, combined with large economic interests are making the application of a IRS in an inland commercial lock technically challenging. Large water volumes can be saved, but this saving is only needed during long dry periods (summer time). The life cycle cost of this saving in water will be really high. Feasibility potential: small A2.1.2 Inland recreational lock Inland recreational lock Availability and waiting times Moderate, depending on economics Intensity and distribution intensity Operation by day, intensity peaks during summer Dimension 80 by 9 m Lift 0 to 1,5 m Water saving Small water saving Benefits salt intrusion No Cost, total benefits Average cost, small benefits Table A 2 Qualitative assessment feasibility potential inland recreational locks. The application of a IRS in an inland recreational lock is technically more feasible than in the case of an inland commercial lock. The smaller availability requirements, smaller operation intensity and longer acceptable waiting times are making the structure technically more feasible. As a result of the smaller dimensions, the saved water volume is small. This makes the application of a IRS generally not needed and therefore economically less feasible. Feasibility potential: small Steffen Woudstra

136 A2.1.3 Coastal commercial lock Coastal commercial lock Availability and waiting times Strict, depending on economics Intensity and distribution intensity Day and night, all year long Dimension 300 by 24 m Lift 0 to 3 m Water saving Large Water saving Benefits salt intrusion Maybe benefits salt intrusion Cost, total benefits High cost, large benefits Table A 3 Qualitative assessment feasibility potential coastal commercial locks. As stated before the high navigation intensity and large requirements for the availability, combined with large economic interests are making the application of a IRS in commercial locks technically challenging. Large water volumes can be saved, but this saving is only needed during the dry part of the year. Additionally a reduction of salt water intrusion during high tides could result in more benefits. Feasibility potential: average A2.1.4 Coastal recreational lock Coastal recreational lock Availability and waiting times Moderate, depending on economics Intensity and distribution intensity Operation by day, intensity peaks during summer Dimension 90 by 9 m Lift 0 to 3 m Water saving Average water saving Benefits salt intrusion Average benefits salt intrusion Cost, total benefits Average cost, average benefits Table A 4 Qualitative assessment feasibility potential coastal recreational locks. Technically the application of a IRS in an coastal recreational lock is more feasible than in a coastal commercial lock. This is caused by the smaller availability requirements, and smaller operation intensity and longer waiting times. Saving of water is usually not needed in this case, but could be preferable during long dry periods. Feasibility potential: small A2.1.5 Selection of a case situation The application of an IRS in inland locks is less feasible according to the above results of the assessment. At present in commercial locks the IRS concept could be of use. Potentially the IRS Lock could be competitive for locks equipped with measures against salt intrusion and measures for saving the water loss. On the other hand, small waiting times and high availability (economics) and high reliability norms are making the solution technically hard. In that sense a recreational lock is more attractive, but this type of lock has a much smaller need for saving water. Because of the water saving potential, a coastal commercial lock is selected as the best alternative for the case. In this case a lot of technical challenges are remaining. 122 Master thesis Application of an IRS in a navigation lock

137 A2.2 SELECTION OF A CASE FROM PRACTICE A large coastal commercial lock will be used as case environment. In locks for CEMT class V and smaller usually only an air bubble screen or flushing are used to reduce salt intrusion. Measures for reducing the loss of fresh water are normally not applied in these locks. The coastal locks where CEMT class VI vessels or higher can be expected are gathered in Table A 5. More information is given about the existing measures against water losses and salt intrusion in these locks. Lock complex Waterway (salt fresh) Fresh water loss measures Salt intrusion measures Average lift (m) 24 Highest section IJmuiden North Sea North Sea No measures Air bubble 0,42 Salt Canal screens, flushing Krammer Krammer - Volkerak Adjusted Adjusted 0,11 Fresh Dunkirk system Dunkirk system Volkerak Hollands Diep - No measures Air bubble 0,38 Salt Volkerak screen Kreekrak Schelde Rijnkanaal - Dunkirk system Dunkirk system 1,65 Salt Zoommeer Terneuzen Western Scheldt Gent-Terneuzen Canal No measures Salt water pit, flushing, air bubble screen 2,04 Fresh Table A 5 Potential locks for the case study. The Kreekrak locks separate the (permanent) higher salt water level of the Scheldt Rijn Canal. The permanent higher water level makes that the lock has similar properties as regular inland locks. The other locks are all connected to a waterway were a tidal movement in the water level exists. As a result of the tide the lift over these locks can be both positive and negative. The lift of the locks with a tide is on general small, and therefore the water losses will be relatively small. South of the Terneuzen locks, in the fresh Gent-Terneuzen Canal, the target water level is +2,13 m NAP. In the case of the Terneuzen Locks most of the time a positive, and compared to the other locks, a large lift is available. This makes the Terneuzen Lock Complex an appropriate case for the study of the feasibility of the IRS Lock. 24 [L15] Rijkswaterstaat, Waternormalen, Steffen Woudstra

138 A2.3 DESCRIPTION OF THE TERNEUZEN LOCK COMPLEX The dimensions of the design vessels and lock chambers in the Terneuzen Lock complex will be described. All dimensions of the locks and vessels are found in the document Features of waterways in The Netherlands 25. Also a description of the water management in the lock complex is given. A2.3.1 Western Lock The Western lock is the largest lock in the Terneuzen Lock complex. The lock chamber is filled and emptied with the help of a longitudinal culvert system. The dimensions of the Western Lock are based on a Panamax vessel. A short description of the properties of the Western Lock is given in Table A 6. In Table A 7 the maximum vessel dimensions of the Western Lock chamber are given. Property Western Lock Length 290 m Width 38 m Depth 13,5 m (-11,37 NAP) Bottom level -12,82 m NAP Water management measures Salt water pit, flushing, air bubble screen, intermediate gate. Ship passages (2005) (40%) sea vessels, 6045 (35%) inland vessels, 4444 (25%) non-cargo carrying vessels. Total: Table A 6 General properties Western Lock. Maximum vessel dimensions (m) Length x width Draught Fresh Salt 265 x 37 12,5 app. 12,2 Table A 7 Maximum vessel dimensions Western Lock. A2.3.2 Middle Lock The middle lock has a lock chamber length of 140 meter. In this section the width of the lock chamber is 25 meter. The width in the approach routes is 18 meter. The Middle Lock is a tidal lock which can only be used when the water level at the Western Scheldt is at least -0,50 m NAP. In Table A 8 the properties of the lock are given. Property Middle Lock Length 140 m Width 24 m at lock chamber, 18 m at approach routes Depth 8,63 m Water management measures Intermediate gate, flushing. Ship passages (2005) 1357 (11%) sea vessels, 8945 (75%) inland vessels, 1688 (14%) non-cargo carrying vessels. Total: Table A 8 General properties Middle Lock. 25 [L14] Rijkswaterstaat, Vaarwegkenmerken in Nederland, February [L24] Nederlandse Adviesdienst Verkeer en Vervoer, Rapport verkeersgegevens sluis Terneuzen, March Master thesis Application of an IRS in a navigation lock

139 When the water level is at least -0,50 m NAP, vessels with a draught of 6 meter are allowed. The maximum draught can be increase until 7,25 meter in case the water level is at least +0,75 m NAP. In Table A 9 the maximum vessel dimensions are presented. Maximum vessel dimensions (m) Length x width Draught Fresh Salt 115 x 16 (sea vessels) 6-7,25 5,85-7,1 140 x 16 (inland vessels) 6-7,25 5,85-7,1 Table A 9 Maximum vessel dimensions Middle Lock. A2.3.3 Eastern Lock The Eastern Lock is especially build for inland vessels. The maximum draught of the vessels using the Eastern Lock is limited to 4,3 meter for push barges. In Table A 10 the properties of the Eastern Lock or given. In Table A 11 the maximum vessel dimensions for the Eastern Lock are presented. Property Eastern Lock Length 290 m (low tide) or 260 m (high tide) Width 24 Depth 4,5 m Water management measures Intermediate gates, flushing. Ship passages (2005) 197 (0,5%) sea vessels, (90,8%) inland vessels, 3294 (8,7%) non-cargo carrying vessels. Total: Table A 10 General properties Eastern Lock. Maximum vessel dimensions (m) Length x width Draught Fresh Salt 70 x 23 (sea vessels) 4 app. 3,9 200 x 23 (push barges) 4,3 app. 3,9 140 x 23 (inland vessels) 4 app. 3,9 Table A 11 Maximum vessel dimensions Eastern Lock. A2.3.4 Future Large Sea Lock The Terneuzen Lock complex is forming a bottleneck for vessels navigating to and from the port of Gent. In March 2012 authorities in The Netherlands and the Flanders area coincided about further expansion of the capacity of the Terneuzen lock complex. The so-called Large Sea lock is planned situated next to the Western Lock. The existing Middle lock has to be demolished in order to create the space for the new lock chamber. The dimensions of the new lock chamber will be based on a Post-panamax vessel (366 x 49 x 14,5 meter). The dimensions are gathered in Table A 12. Length (m) Width (m) Depth/draught (m) Lock chamber (between inner gates) Design vessel ,5 Table A 12 Dimensions lock chamber and design vessel Large Sea Lock. Steffen Woudstra

140 A2.3.5 Quantitative water management In general situations water from the Gent-Terneuzen Canal is discharged into the Western Scheldt during the locking cycles or by flushing. Flushing is executed when the water level in the Gent- Terneuzen Canal reaches +2,38 m NAP (target level plus 0,25 m). At first only the longitudinal culvert of the Western Lock are used for flushing. The inlet openings of the longitudinal culverts are placed under the inner lock head. The outlet on the outer side has the form of a perforated base plate. Despite of the culverts the currents from the flushing are resulting in hindrance for shipping. Continuous flushing can be executed in order to flush intruded salt water back into the Western Scheldt or in order to discharge a surplus of water. In such situations a the discharge capacity in the Western Lock is 35 m 3 /s. In case a larger discharge capacity is needed, the Middle Lock is used for flushing and in exceptional cases also the Eastern Lock can be used. The capacity of the flushing facilities of the total Terneuzen Lock complex is 170 m 3 /s. Water supply into the GTC is managed with the goal of maintaining the target water level and reducing the salt intrusion in the Gent-Terneuzen Canal. According to agreements between the Dutch and Belgium governments the minimum water supply from Belgium is 13 m 3 /s average over a period of two months. A2.3.6 Qualitative water management Salt water from the Western Scheldt is entering the Gent-Terneuzen Canal through the Terneuzen locks. The Dutch and Belgium government coincided on a target level of +2,13 m NAP and a maximum salt content of maximum 3,5 grams per litre in the water 2200 meter south of the Western Lock. The chloride concentration in the Gent-Terneuzen Canal is in usual situations between 1 and 3 grams per litre. A combination of measures is applied in the Terneuzen Lock complex in order to reduce salt intrusion through all the lock chambers. Possibility for flushing for all lock chambers Air bubble screens Intermediate gates Salt water pit (only in front of the Western lock) Behind the Western Lock a salt water pit is applied in order to cumulate salt water that intrudes into the Gent-Terneuzen Canal. From there the salt water can be flushed back into the Western Scheldt under free flow, since most of the time the water level in the Gent-Terneuzen Canal is higher than the water level in the Western Scheldt. The discharge during flushing is limited since the currents result in hindrance for vessels and the fresh water loss often has to be limited (dry periods). Because of mixing, a volume of more or less 1,8 times the volume of the salt water has to be discharged during flushing. After monitoring of the effectiveness of the system against salt intrusion, additional air bubble screens were placed in order to prevent a complete exchange of the salt water in the lock chamber. 126 Master thesis Application of an IRS in a navigation lock

141 Appendix 3 SHAPE AND EQUILIBRIUM IRS IN LARGE SEA LOCK In this chapter a first design of the IRS in the future Large Sea Lock is made. First the layout of the lock chamber has been designed. Thereafter the shape and equilibrium of the sheet has been calculated. A3.1 LAYOUT AND DIMENSIONS LARGE SEA LOCK The lock chamber of the Large Sea Lock has to be at least 427 meter long, 55 meter wide and 16 meter deep. Since the Gent-Terneuzen Canal and the Western Scheldt are waterways designed for CEMT classes larger than 5, the norms in the Waterway Guidelines 27 are not applicable (the norms are only applicable for class 1 to 5). The draught of the design vessel is 14,5 meter in fresh water. In the determination of bottom levels and sill depths the draught of vessels and the keel clearance are important aspects. First a rule of thumb is used for the keel clearance for commercial vessels. For fresh water this rule of thumb is 10% of the maximum draught. For salt water, the rule of thumb is 12,5%. The keel clearance for salt water is larger since some extra safety is needed for the case that the water is less salt than expected. The bottom levels and levels of the sills are determined relative to the Lower Astronomical Tide. An overview of the designed bottom levels, sill levels and the water levels is given in Figure A 1. Bottom level of the Gent-Terneuzen Canal It is expected that in the near future the Gent-Terneuzen canal will be deepened to 16 meter depth during the target water level of +2,13 NAP. The 16 meter is the maximum possible depth. The depth is restricted by the Sluiskiltunnel which is a tunnel crossing the Gent-Terneuzen Canal near Sluiskil. For this thesis a depth of 16 meter is assumed which results in a bottom level of -13,87 m NAP. Sill depth at Gent-Terneuzen side The sill depth at the canal side should be such that all vessels using the Gent-Terneuzen canal can also use the navigation lock. This means a sill depth of 16 meter during the target water level in the Gent-Terneuzen Canal is sufficient. Hence, the sill depth will be equal to the bottom level of the Gent-Terneuzen Canal: -13,87 meter. Sill depth at Western Scheldt side The sill at the Western Scheldt side should at least be located at such a depth that tidal independent vessels can always enter the lock. The depth of the navigation routes in the Western Scheldt equals the draught of the tidal independent design vessel of 13,1 meter relative to LLWS (Low Low Water Spring) increased with a the keel clearance for salt water. With the applied keel clearance of 12,5%, the design depth of the navigation routes in the Western Scheldt becomes 14,75 m. Nowadays the depth for tidal waters is given relative to LAT. For Terneuzen this results in a sill depth of 14,5 m LAT, which equals -17,19 m NAP. The tidal dependent Post-panamax design vessel should be able to enter the lock from the Western Scheldt. The draught of this vessel is 14,5 meter in fresh water and more or less 14,2 meter in salt water. With an additional keel clearance a depth of 16 meter is needed. When the sill is applied at the before determined -17,19 NAP, the tidal dependent vessel can enter the lock for water levels of at least -1,19 NAP. The design vessels is than tidal dependent, but this seems acceptable since waiting times will be small under general conditions. 27 [L23] Rijkswaterstaat Dienst Verkeer en Scheepvaart, Richtlijnen Vaarwegen 2011, December Steffen Woudstra

142 Bottom level lock chamber The bottom level of the lock chamber needs to be at least as deep as the lowest sill, which is in this case -17,19 m NAP. First the bottom is designed at -17,19 m NAP. For the design of the IRS Lock the bottom level can be lowered in order to create space for the IRS. The bottom in the lock chamber and the level of the sill at the Western Scheldt side are both -17,19 m NAP. Bottom level in front of the lock at the Western Scheldt side When the tidal dependent design vessels is not able to join a lock cycle, the vessel has to wait in front of the lock. Since the design vessel is tide dependent, it is also possible that the design vessel has to wait in front of the lock until a higher water level is available. With the keel clearance taken into account a depth of 16 meter is needed relative to the Lowest Astronomical Tide. This gives a bottom level of -18,69 m NAP in the Western Scheldt close to the lock. Height lock chamber walls The choice for the top level of the lock chamber walls of locks used by sea vessel is based on local conditions and the type of vessels using the lock. The top of the walls of the Western Lock is located at +6,0 m NAP. For the Large Sea Lock the top of the lock chamber walls is assumed to be located at the same level. For the feasibility of the IRS Lock the height of the lock chamber is not an important factor. Eventually the height of the walls can be easily adjusted during a later phase of the design. Minimum and maximum lockage level The minimum and maximum lockage level for CEMT class 5 and smaller is given as the 1% lowest and highest water level. In the Large Sea Lock, the minimum and maximum lockage levels are determined based on the situation and boundary conditions. Amongst others the levels depend on available height under bridges and the available depth in the waterways. For the Large Sea Lock the 1% values of +3,40 m NAP en 2,78 m NAP are used. This gives a depth of 20,59 m respectively 14,41 meter. The water levels present in the lock chamber and the designed bottom levels are given in the cross section of the lock chamber in Figure A 1. Figure A 1 Water levels and bottom levels for the GTC and WS. 128 Master thesis Application of an IRS in a navigation lock

143 A3.1.1 Facilities and equipment Part of the space in the lock chamber has to be reserved for the filling and emptying system and other facilities like fenders. Some assumptions about the location and dimensions of these facilities and equipment will be done. The assumptions will be done with the existing facilities in the Western Lock as a reference. An overview of the assumed lock layout is given in Figure A 2. Lock gates The type of lock gates are usually chosen based on the closure width and the head difference over the gates. In this case a closure width of at least 55 meter is needed and for such a situation only roller gates are applicable. Since the Large Sea Lock is part of a primary sea defence, double roller gates are applied at the Western Scheldt side. Levelling system For the first design of the future Large Sea Lock a similar system as applied in the Western Lock is used. In the Western Lock a longitudinal culvert is applied that has an inlet near the bottom at the canal side of the inner gate. The outlet at the Western Scheldt side of the lock takes the form of a perforated base plate. Two transverse culverts are used to join the longitudinal culvert with the lock chamber. The transverse culverts enable water to flow into the lock chamber via a perforated base plate. For the first design of the future Large Sea Lock a similar system is assumed where filling and emptying takes place with help of a longitudinal filling and emptying system. Two areas of 30 meter long covering the total width of the lock chamber are reserved for the inlets in the lock chamber. According to a lock specialist the areas reserved for the filling and emptying system are quit large. The areas are situated at a quarter of the length from both gates. The total length of the lock chamber between the inner gates is 427 meter. When the areas for the inlets are subtracted from the total length, totally 367 meter length is remaining for the inflatable IRS. This 367 meter is subdivided into three areas by the two inlets. The middle area is 183,5 meter and the two areas at both ends have a length of 91,75 meter. Fenders Fenders are assumed to be applied at both lock chamber walls over the total length between the lock gates. The width of the fenders is assumed to be 2 meter. It is also assumed that safety facilities like ladders will fit in this space. Floating fenders are assumed that are located at the water level. The effective width of the lock chamber has to be 55 meter. Hence, the inner width of the lock chamber becomes 59 meter. Figure A 2 Design layout Large Sea Lock. Steffen Woudstra

144 A3.2 2D STATIC EQUILIBRIUM IRS IN LARGE SEA LOCK With help of the adjusted Excel sheet of Dirkmaat, a first estimation of the 2D static equilibrium of an IRS for the future Large Sea Lock has been made. The goal was to keep the membrane force as small as possible, thus, also the inner pressure was kept small. The maximum water level in the Gent-Terneuzen Canal for which the IRS will be used is applied as external load. The depth above the lock chamber floor becomes 19,44 meter. This is a realistic scenario for dry periods. An equilibrium shape is found and plotted in Figure A 3. Only a crest height of 2,45 meter was reached. Solutions closer to a crest height of 2,5 meter are not realistic anymore, since the small differences in crest height depend on really small adjustments of the initial angle (or inner pressure). These small adjustments have no meaning in practice. The input leading to the equilibrium is gathered in Table A 13. Equilibrium input for Large Sea Lock Water depth 19,44 m Sheet width 59,3 m Base width 59 m Inner pressure 2,05 bar Membrane force 5600 kn/m Angle initial element 3,0 rad Table A 13 Input for equilibrium in the IRS applied in the Large Sea Lock. The membrane force for the static equilibrium was found to be 5600 kn/m. Additional dynamical external loads, like flows by vessels and lock operations, can lead to a larger membrane force. Also discontinuities in the sheet can lead to stress concentrations. Besides, also safety factors have yet not been taken into account so far and these will lead to a higher required strength. All by all a sheet with a larger tension strength than 5600 kn/m will needed. Figure A 3 Shape of the sheet for the Large Sea Lock. 130 Master thesis Application of an IRS in a navigation lock

145 Previously the future Large Sea Lock has been selected as a case environment for the IRS Lock. The idea was that the larger the lock chamber, the larger is the potentially saved volume of water. The larger the saved volume, the larger the economic benefits. At the same time the size of an IRS is limited by technical issues as the strength of the rubber sheet. After further analysis of the membrane forces in the rubber sheet it became clear that previously some technical disadvantages of IRSs had been underestimated. These disadvantages are: As a result of the overpressure along the sheet, a larger sheet (width) leads to larger membrane forces. The strength of the sheet is limited. A large water depth leads to a large internal pressure. The larger the internal pressure the more time and pumping capacity is needed for the inflation and deflation of the IRS. The membrane forces can be reduced by: Making the width of the sheet and the base width smaller. The application of a smaller overpressure. At the same time the overpressure can t be too small as the overpressure is needed to give the IRS some stiffness. Reducing the height of the IRS. This will lead to a smaller size of the overpressure in the top of the IRS. Using a combination of an air and water filler. The sheet of the Ramspol barrier had an initial strength of 1870 kn/m, after ageing and relaxation the strength was found to be 970 kn/m. Van Breukelen 28 found that the largest strength of regular reinforced rubber sheets is 4000 kn/m (conveyor belts). Hence, it doesn t seem economically feasible to produce a sheet with a strength of at least 5600 kn/m. The only feasible possibility limiting the membrane forces is to apply several smaller IRSs. But then still a large internal pressure is needed because the large depth of the lock. Hence, it is better to look for a smaller coastal commercial lock chamber with a smaller width and depth. 28 [L9] M. van Breukelen, Improvement and scale enlargement of the inflatable rubber barrier concept, December Steffen Woudstra

146 Appendix 4 ASSESSMENT ALTERNATIVES MULTI CRITERIA ANALYSIS In this appendix a more extensive description of the alternatives for the IRS Lock will be given. Also the Multi Criteria Analysis is extensively described. A4.1 ALTERNATIVES In this paragraph the five alternatives for the IRS Lock that have been developed are more extensively described. A4.1.1 Rubber sheet connected to the walls Figure A 4 Impression alternative 1: Sheet connected to the walls. In Figure 47 an impression of the cross section of the alternative Rubber sheet connected to the walls is given. In length direction the rubber sheet is connected to the lock chamber walls. At both ends the sheet needs to be connected to the lock chamber floor. The width of the rubber sheet (L) is limited and is relatively small compared to the base width (B). The base width is the width between the parallel clamp lines of the sheet is meant. The ratio of L/B indicates the relative overlength of the sheet. Overlength that can lead to the formation of flaps during the inflation and deflation process. The perimeter of the lock chamber floor is equal to the width of the rubber sheet. In deflated state the rubber sheet will easily fit the lock chamber bottom, which has also a positive effect on fold formation. An under pressure or the addition of extra weight to the sheet will keep the sheet stable while deflated. Eventually a small overlength of the bottom recess can be applied for a better storage in deflated state. The advantages of this alternative are listed below: Limited fold formation because of small L/B compared to existing inflatable IRSs. The structure is simple and doesn t consist of parts that require a lot of maintenance. Operation of the structure is simple and can be executed in a relatively short time. The disadvantages of this alternative are: The shape of the rubber sheet close to the ends of the IRS is complex. The sheet will often move around the connections during the inflation and deflation process. The repeating movement and loads make the sheet susceptible for fatigue. Close to the lock chamber floor the width between the walls becomes smaller by the curved shaped of the bottom recess. The keel clearance of vessels always has to be guaranteed. 132 Master thesis Application of an IRS in a navigation lock

147 A4.1.2 Rectangular shaped structure Figure A 5 Impression alternative 2: Rectangular shaped structure. This alternative consists of an IRS kept in a rectangular shape by frames. The frames need to be stiff to prevent too much bending as a result of the overpressure inside the IRS. The frames can be placed at the inner side of the structure but also at the outer side. A freeboard is applied around the structure to prevent interaction with the lock chamber walls. The shape of the rubber structure is equal to the shape of the lock chamber. This makes the potential water volume that can be saved really large. The advantages of this alternative are: The shape is effective and the water saving potential is large. The structure can be inflated and deflated in a uniform way and there are no problems with flaps. The structure will be relatively stable in deflated state by the weight and stiffness of the frames. The connection of the sheet to the lock chamber floor is simple. The disadvantages of this alternative are: The frames need to be really stiff to prevent too much bending. The frames will adds extra weight to the structure. In deflated state large folds will occur between the frames and the frames will result in peak loads at the rubber sheet. Frames at outer side of the structure will be hard to construct since large tensile stresses will act in the frame and the connections at the corners need to be really stiff. If steel frames are applied these frames are sensitive for corrosion and maintenance. For frames at inner side of the rubber structure internal stiffeners can easily be applied. On the other side, the connection of the rubber sheet to the frames needs to be really strong and will be complex. Frames at the inner side are hard to reach in case maintenance is needed. In the corners of the IRS large stress concentrations can occur. Steffen Woudstra

148 A4.1.3 Rubber structure controlled by cables Figure A 6 Impression alternative 3: Rubber sheet controlled by cables. This alternative has a similar construction principle as an airbed. The shape of the structure is controlled with the help of cables. In the choice of placing the cables at the inner side or the outer side of the structure, the same advantages and disadvantages as for the frames in the alternative Rectangular shaped structure play a role. If the cables are placed at the inner side, the connections between the sheet and cables will become complex. Since large tension forces will occur, a lot of cables will be needed to spread the tension load. A freeboard is applied around the structure to prevent interaction with the lock chamber walls. The advantages of this alternative are: The shape and behaviour of the rubber structure during the inflated phase can be controlled with help of the cables. Due to the cables the tension force in the rubber sheet will be smaller. The shape of the rubber structure is effective and the water saving potential is large. Cables at the outer side of the structure are relatively easy to construct since a connection with the rubber sheet is not absolutely necessary. The disadvantages of this alternative are: In the deflated phase the rubber sheet is instable. The sheet has a large overlength (large L/B). Folds will form during deflation and air bubbles can be present in the rubber structure. Cables at the outer side of the structure need a corrosion protection and periodically maintenance or replacement. If placed at the inner side, the cables are hard to reach for maintenance. When cables are applied at the inner side of the structure, the connections with the rubber sheet are complex. 134 Master thesis Application of an IRS in a navigation lock

149 A4.1.4 Perforated floor Figure A 7 Impression alternative 4: Perforated floor. In the alternative Perforated floor the rubber structure is placed in a basement under the lock chamber. The lock floor is perforated and water can flow easily between the basement and the lock chamber. The perforated floor can be considered as a barrier between the rubber structure and the vessels in the lock chamber, breaking jet flows and currents by ship propellers and protecting the rubber structure for damage. Possibly the rubber structure can be inflated really fast since currents resulting from the inflation will not directly hit the vessels. The advantages of this alternative are: The IRS is protected from direct impact of jet flows and currents. There is no risk for collision between vessels and the rubber structure. Potentially really quick filling and emptying of the rubber structure is possible because of smaller hindrance for vessels by flows. Also less strict requirements for the behaviour of the sheet will exist since the minimum keel clearance for vessels is always present. During the deflated state less measures are needed to keep the rubber sheet stable since the hydraulic loads will be smaller. Several compartments in horizontal plane will lead to a structure with a small risk of total failure. The disadvantages of this alternative are: The construction of the basement at a large depth will be complex and expensive. The perforated floor will have a large width and length. When the floor is constructed out of concrete intermediate columns will be needed to support the floor. The columns will restrict the space for the rubber structure and several smaller rubber structures will have to be constructed. Maintenance and inspection of the rubber structure are hard since the structure is hard to reach and located at a large depth. When the lock chamber is pumped dry for maintenance measures need to be taken preventing floating up of the lock chamber. Steffen Woudstra

150 A4.1.5 Flaps acting as side plates Figure A 8 Impression alternative 5: Flaps acting as side plates. In this alternative stiff flaps are connected to the lock chamber bottom by hinges. During the inflation the flaps will rotate until they reach a vertical position where the flaps are stopped. In the deflated phase the flaps should cover the rubber sheet partly and in this way guarantee a stable storage. Besides, the flaps will protect the rubber sheet. A stiff plate or stiffeners on top of the structure have to prevent the formation of air bladders during the deflation and promote a uniform deflation. A freeboard is applied around the separated rubber structure. The advantages of this alternative are: During the deflated phase the rubber sheet is protected by flaps and the flaps are guaranteeing a stable storage. The shape in inflated phase is relatively stable. The shape is effective and the water saving potential is large. The disadvantages of this alternative are: The behaviour during deflation is hard to control and large folds or air bubbles can be formed during the deflation. The hinges under water will need maintenance periodically. The height of the structure is limiting the length of the flaps and in that way the area of the rubber sheet that can be covered by the flaps. At the ends of the rubber structure no flaps are applied and the rubber sheet isn t stable in deflated state. The hinges and sheet both need a connection to the lock chamber floor. The sheet needs to be connected to the plates and the plates to the hinges. The constructability of this alternative is a disadvantage. Inflation and deflation has to be done in a controlled way, this will result in extra time needed for operation of the structure. The deflation process has to be done in a controlled way and is sensitive for the formation of air bubbles. 136 Master thesis Application of an IRS in a navigation lock

151 A4.2 EXPLANATION OF ASSESSMENT MCA CRITERIA An explanation of the ranking for each alternative for each criterion of the MCA is given in this paragraph. Robustness 1) Sheet connected to walls 2 For different kinds of loads and load directions this alternative performs well. The sheet can deform but no large deformations or displacements are expected in case of changing loads. 2) Rectangular shape 4 This alternative is sensitive for unexpected horizontal loads perpendicular to the length direction. Large deformations can occur at the top of the structure. 3) Controlled by cables 3 The cables are placed such that the structure performs well for expected loads. 4) Perforated floor 1 This alternative the most robust since unexpected loads will be diminished by the perforated floor and the structure is located in a protected environment. 5) Flaps acting as side plates Table A 14 Explanation ranking alternatives for the criterion robustness. 5 The flaps or sensitive for a change of loads, in case of horizontal loads perpendicular to the flaps the flaps can fold to the inner side of the rubber structure. Maintainability 1) Sheet connected to walls 1 The sheet connected to walls solution is a relatively simple solution and maintenance can be executed from the inner side of the structure. 2) Rectangular shape 3 See controlled by cables. Replacement of the guiding structure is hard. Periodic maintenance is needed. 3) Controlled by cables 2 The cables and connection between cables and rubber sheet need periodic maintenance or replacement. The structure is easy accessible and maintenance can be predicted. 4) Perforated floor 5 The rubber sheet is hard to reach for maintenance and inspection since the rubber structure is located in the basement. 5) Flaps acting as side plates 4 The hinges placed under water need period maintenance. The hinges can be covered by a flap to keep them in a dry environment, but then the hinges are hard to reach in case of maintenance or failure. Table A 15 Explanation ranking alternatives for the criterion maintainability. Steffen Woudstra

152 Stability 1) Sheet connected to walls 4 During inflated state the structure is relatively stable but deformation of the shape is possible. During deflation air bubbles can form in the middle of the structure. In deflated state an under pressure can be applied to guarantee a stable storage. 2) Rectangular shape 1 The shape of this structure is controlled during inflated state. During deflated state the frames will keep the rubber sheet stably in place. 3) Controlled by cables 5 In inflated state the structure will be stable, but during deflated state and the inflation and deflation state the structure isn t stable. 4) Perforated floor 2 Since the rubber structure in this alternative is placed in a protected environment, the structure will be relatively stable. 5) Flaps acting as side plates Table A 16 Explanation ranking alternatives for the criterion stability. 3 The flaps result in a controlled inflation process and a stable situation during deflated state. During deflation and the inflated state the structure will be sensitive for large deformations of the shape. Constructability 1) Sheet connected to walls 1 This alternative is relatively easy to construct since not a lot of parts are needed. The only negative thing is the shape of the lock chamber floor, which is a bit complex at the ends. 2) Rectangular shape 4 The guiding frames are hard to construct since a large stiffness of the frame and stiff connections in the frame are needed. 3) Controlled by cables 2 This structure is relatively easy to construct if the cables are placed at the outer side of the structure. Additional connections between the cables and rubber sheet and the cables and lock chamber floor are needed. 4) Perforated floor 5 The basement in this alternative is hard to construct since the basement is located at a large depth. Besides, the larger depth asks for extra measures against floating up of the lock chamber. 5) Flaps acting as side plates 3 The connections between the flaps, hinges and rubber sheet are resulting in a lot of work, but the work is simple. Table A 17 Explanation ranking alternatives for the criterion constructability. 138 Master thesis Application of an IRS in a navigation lock

153 Volume of saving 1) Sheet connected to walls 4 The shape is half elliptical and the structure has no horizontal freeboard. A vertical freeboard is needed for the formation of air bubbles during deflation. A fourth place. 2) Rectangular shape 1 This alternative has a really effective rectangular shape and the freeboard around the structure is minimal since the structure is relatively stable. 3) Controlled by cables 2 The solution with cables also has an effective rectangular shape. 4) Perforated floor 5 The half cylindrical shape of the structure is ineffective. 5) Flaps acting as side plates 3 The alternative has a rectangular shape but the freeboard is larger since the structure is less stable. Table A 18 Explanation ranking alternatives for the criterion volume of saving. Operation time 1) Sheet connected to walls 2 The structure can easily be quickly inflated and deflated since no parts like flaps are a guiding structure need a controlled way of inflation and deflation. 2) Rectangular shape 3 The structure can be operated easily but some time is needed to deflated the structure in a controlled way and prevent damaged to the sheet by the frame. During quick deflation the frame could fall upon the rubber sheet resulting in damage. 3) Controlled by cables 4 It is hard to control the deflation process of the rubber structure controlled by cables. 4) Perforated floor 1 Quick inflation and deflation of the rubber structure in this alternative is possible since the currents caused by these operation are not directly acting on the moored vessels. 5) Flaps acting as side plates 5 The deflation process need to be controlled really well in order to prevent instable parts of the sheet in deflated state which are not covered by the flaps. Table A 19 Explanation ranking alternatives for the criterion operation time. Fold formation and fatigue 1) Sheet connected to walls 1 The connections of the sheet to the walls are sensitive for fatigue. No large folds will occur if some overlength is applied in the bottom recess. 2) Rectangular shape 5 Large folds will exist between the frames in the deflated state. 3) Controlled by cables 3 The structure is sensitive for large fold formation around the cables. Stress peaks are likely to occur in the folds. 4) Perforated floor 2 Folds will form in the deflated state but it is not expected that these folds will always occur at the same location. 5) Flaps acting as side plates 4 The connection between the flaps and plates is sensitive for fatigue. During deflated state large folds can occur. Table A 20 Explanation ranking alternatives for the criterion fold formation and fatigue. Steffen Woudstra

154 Investment cost 1) Sheet connected to walls 1 The structure is relatively simple and not much parts are needed. This makes the investment needed for the alternative relatively small. 2) Rectangular shape 3 The geometry of the rubber sheet and construction of the frames and connections between the frames and rubber sheet are complex, resulting in relatively high investment costs. 3) Controlled by cables 2 The structure is relatively simple but the connection between the steel cables and the rubber sheet are complex. This will make the investment cost relatively small but slightly higher than the investment cost of alternative 1. 4) Perforated floor 5 The investment cost of the large basement and perforated floor and additional measures against floating up are resulting in really high investment cost. 5) Flaps acting as side plates 4 The complex structure with lot of parts and connections has relatively high investment costs. Table A 21 Explanation ranking alternatives for the criterion investment cost. Operational cost 1) Sheet connected to walls 1 This alternative is easy to operate and the inflation and deflation can be done in a constant speed and without special local pressure management. 2) Rectangular shape 2 See alternative 1, the only difference is that the deflation has to be executed in a more controlled (slow) way. 3) Controlled by cables 3 See alternative 2. The stable storage of the rubber sheet after deflation will need some extra time. 4) Perforated floor 5 Since the rubber structure is located at a larger depth, the internal pressure needed to create an overpressure is larger than in the other alternatives. This will lead to extra cost of energy needed to create the pressure inside the structure. From a first estimate it is not expected these cost can be compensated by a quicker inflation and deflation process. 5) Flaps acting as side plates 4 During deflation the flaps have to cover the rubber sheet smoothly. This will require some extra time resulting in more delay for shipping. Table A 22 Explanation ranking alternatives for the criterion operational cost. 140 Master thesis Application of an IRS in a navigation lock

155 Appendix 5 CALCULATIONS FOR THE HEIGHT OF THE OPTIMAL IRS A model with the water levels and lift for the Eastern Lock is used to determine the volume of the water saving as a function of the height of the IRS. The calculations have been executed for the different water levels in the Gent-Terneuzen Canal and Western Scheldt. An optimal height for the IRS has been designed based on the results out of the model. The basis of the model is given in this appendix. Later this basis is elaborated and used for a more precise determination of the total saved volume and total water loss (see paragraph 14.2). clear, clc, clear all, close all; %Input Tide.averagehigh = 2.29; %m NAP %average tide (tide in between spring and neap tide) Tide.averagelow = -1.89; %m NAP Tide.springhigh = 2.67; %m NAP Tide.springlow = -2.13; %m NAP Tide.neaphigh = 1.76; %m NAP Tide.neaplow = -1.56; %m NAP h.canaltarget = 2.13; h.canalhigh = h.canaltarget+0.25; h.canallow = h.canaltarget-0.25; Tlockcycle = 1+1/6; %Lock cycle time (hours), equal to 1 hour and 10 minutes. %Tidal water levels in time z_average = (Tide.averagehigh+Tide.averagelow)/2; A_average = (Tide.averagehigh+abs(Tide.averagelow))/2; T = 24.84; timestep=1/6; %in hours t = [0:timestep:T]; h.wsastr_average = z_average+a_average*sin(2*pi*t/(t/2)); %Plot water levels Western Scheldt and Gent-Terneuzen Canal figure(1); plot(t,h.wsastr_average); title('waterlevels for one tidal cycle','fontsize',22); xlabel('time (hours)','fontsize',18); ylabel('waterlevel (m NAP)','FontSize',18); set(gca,'fontsize',18); hold on; for i=0:t Lift.target_astr = h.canaltarget-h.wsastr_average; end plot([0 t(length(t))],[h.canaltarget h.canaltarget],'r'); hleg1 = legend('mean tide WS','Target level GTC'); set(hleg1, 'Location', 'EastOutside','FontSize',18) hold off; %Plot lift and target level Gent-Terneuzen Canal figure(2); plot(t,lift.target_astr); hold on; plot([0 t(length(t))],[ ],'g'); Steffen Woudstra

156 hold off; title('available lift','fontsize',22); xlabel('time (hours)','fontsize',18); ylabel('lift (m)','fontsize',18); set(gca,'fontsize',18) hleg1 = legend('lift (m)','line 2.5 meter'); set(hleg1, 'Location', 'EastOutside','FontSize',18) %Calculation saved volume as a function of IRS height IRS.height = [0:0.01:max(Lift.target_astr)]; IRS.length = 290; IRS.width = 24; for ii=1:length(irs.height); Oper = Lift.target_astr>IRS.height(ii); Oper_time(ii) = sum(oper); Oper_time_hours(ii) = Oper_time(ii)/(1/timestep); Amount_cycles(ii) = floor((oper_time_hours(ii)/2)/tlockcycle)*2; %Two equal periods of operations in which operation time should happen Saved_volume(ii)=0.8*0.6*IRS.length*IRS.width*IRS.height(ii)*Amount_cycles( ii); end %Plot saved volume as a function of IRS height figure(3); plot(irs.height, Saved_volume); title('saved volume per tidal cycle','fontsize',22); xlabel('height IRS (m)','fontsize',18); ylabel('saved volume (m^{3})','fontsize',18); xlim([0, 4]); set(gca,'fontsize',18) hleg1 = legend('saved volume (m^{3})'); set(hleg1, 'Location', 'EastOutside','FontSize',18); filename = 'Sheetheight.mat'; save(filename); %Calculate total water loss during full tidal cycle when continuous locking %is executed. timestep2=timestep*60; %From hours to minutes j=7:tlockcycle*60/10:length(lift.target_astr); %Defines the moment when a new lock cycle starts. The lift at the start of the lock cycle is used to calculated the water loss. Loss(j)=IRS.length*IRS.width*Lift.target_astr(j); Totallloss=sum(Loss(find(Loss > 0))); 142 Master thesis Application of an IRS in a navigation lock

157 Appendix 6 SELECTION FILLER MEDIUM In the IRS Lock concept initialized by Grontmij the IRS is filled with air. In existing IRSs in a hydraulic environment air fillers, water fillers and a combination of both are common. Water and air are always available close to hydraulic structures and therefore an easy obtainable and a reliable filler medium. The filler medium is of great importance for the structural properties (stiffness) and behaviour of the rubber sheet. Therefore in this appendix will be checked if the use of an air filler is the best solution for the IRS Lock. A6.1.1 Filling and emptying with a only water Water fillers are often used for IRSs. Due to the hydrostatic pressure profile of the water filler the total overpressure along the sheet is smaller and therefore the membrane forces are smaller. Another advantage of a water filler is that water filled structures generally behave more stiff than air filled structures. In case of only a water filler, water from the upper section of the of the waterway (in this case the GTC) is used for filling the IRS. When the IRS is emptied, the water has to flow back into the upper water level. Part of the filling process can occur under free flow. For the total emptying process pumping is needed. From the procedure for filling and emptying the water filled IRS, it is obvious that the water saving procedure is similar to saving water by pumping the water from the lock chamber into the upper section of the waterway. Therefore the IRS brings no additional benefits in the case of a water filler. A6.1.2 Filling and emptying with only air The filling and emptying process is similar as for a water filler. During the inflation of the IRS air is pumped into the IRS until the desired overpressure is available inside the IRS. This process has been described previously in 6.2. A6.1.3 Filling and emptying with a combination of air and water A combination of an air and a water filler can be applied in IRSs. For the Ramspol barrier a combination is used, because it was found that the combination leads to a smaller membrane force than in case only one filler type would be used. The water filler has an advantage for the way the rubber sheet rises or lowers during the inflation and deflation. For a water filler this process happens in a more uniform way. In the design of the IRS Lock this property of the water filler can be used to minimize the impact of the IRS on the available keel clearance. During the inflation first the water filler is used, and after the air filler. In the deflation procedure, first the air is let out of the IRS and thereafter the water. Steffen Woudstra

158 A6.1.4 Selection of a filler medium For the IRS Lock a choice has to be made between only an air filler or a combination of an air and water filler. The alternative fillers are compared based on their performance for technical and economic aspects. The best alternative per aspect will be rewarded with 1 credit. The filler with the largest amount of credits will be selected. The results for the economic aspects are given and explained in Table A 23, the result for the technical aspects are presented in Table A 24. Technical aspects Air filler Air and water filler Explanations Stiffness 0 1 Due to the difference in compressibility an air filled IRS is generally behaving less stiff than a water filled. Membrane forces 0 1 Due to the hydrostatic pressure profile of the water filler the total overpressure along the sheet is smaller and therefore the membrane forces are smaller. Behaviour during inflating and deflating 0 1 Inflating and deflating with water leads to a more uniform rise and lowering of the sheet. Total 0 3 For the technical aspects the combination of the air and water scores best. Table A 23 Comparison technical aspects fillers. Economic aspects Time needed for inflation and deflation Air filler Air and water filler Explanations 1 0 Filling and emptying an IRS with only air can be executed continuously without the need to change the filler medium. Safety 0 0 Both filler have the risk for a blow out and total collapse. Maintenance 1 0 For a combination of fillers two separated systems for filling and emptying or needed. Inlets and conduits for air are more easy accessible and due to the dry environment less maintenance is needed. Cost and benefits 1 0 A single system for filling and emptying just with air will lead to a more simple design and a cheaper system. Also the filling and emptying process will take less time as only a single system is used instead of two systems serial to each other. The benefits (saved volume) will be equal. Total 3 0 The air filler scores best for the economic aspects. Table A 24 Comparison economic aspects fillers. After comparing both alternatives the air filler scores best for the economic aspects but the combined air and water filler scores best for the technical aspects. It should be noted that for the combination of both fillers the desired water level inside the IRS has a large effect on the extent in which technical benefits are present, while the economic disadvantages are always present. In accordance with the initial idea of Grontmij only an air filler is applied. 144 Master thesis Application of an IRS in a navigation lock

159 Appendix 7 CALCULATION HYDRAULIC LOADS ACTING ON THE IRS The different types of loads are inventoried in the main thesis report. Here the load combinations that can occur per phase will be described. In Figure 38 (paragraph 6.2.1) the operations during a lock cycle are given per phase of use of the IRS. This diagram is helpful for determining the load cases. Also the calculations of the loads will be more extensively described. In the calculations the initial bottom level of -7,44 m NAP is used. First the load cases will be described per phase of use. Inflation phase During the inflation phase the gates are closed, the vessels are moored and levelling has been executed before the inflation of the IRS starts. Load case: Hydrostatic pressure Inflated phase During the inflated phase the lock gates will be opened, vessels will navigate outside and into the lock and the gates are close again. Load cases: Hydrostatic pressure + gate operations Hydrostatic pressure + external loads Hydrostatic pressure + moving vessels Hydrostatic pressure + gate operations + moving vessels Hydrostatic pressure + external loads + moving vessels Deflation phase The gates are closed and vessels are moored. The IRS is inflated. Load case: Hydrostatic pressure Deflated phase During wet periods when the IRS is not used, the normal lock cycle will be executed with the IRS deflated at the bottom of the lock chamber. For exceptional high water levels in the GTC flushing will be executed during the deflated phase. Therefore all loads can occur during the deflated phase. Load cases: Hydrostatic pressure + gate operations Hydrostatic pressure + levelling operations Hydrostatic pressure + flushing Hydrostatic pressure + external loads Hydrostatic pressure + moving vessels Hydrostatic pressure + gate operations + moving vessels Hydrostatic pressure + external loads + moving vessels Steffen Woudstra

160 A7.1 HYDROSTATIC PRESSURE Since the IRS is completely submerged a hydrostatic pressure is acting on the IRS. The range of water levels on top of the IRS determine the range of hydrostatic pressures acting on the IRS. The hydrostatic pressure can be calculated with: Where: ρ = mass density of water [kg/m 3 ] g = gravitational acceleration [m/s 2 ] h = water depth [m] Two situations are distinguished, the inflated and the deflated state. Inflated phase The IRS is inflated when the water level of the GTC is available in the lock chamber. In practice the smallest water level in the GTC between the year 2000 and 2011 was +2,0 m NAP 29. According to agreements between the Dutch and Belgium government, the minimum water level in the GTC may be +1,88 m NAP. The IRS can be applied for a higher water level than the target water level in case water is saved in the GTC as a buffer for an expected dry period. Hence, the maximum level for which the IRS is used is chosen as +2,25 m NAP. The IRS will be inflated for water levels from +1,88 m NAP to 2,25 m NAP. The hydrostatic pressure is calculated for the minimum and maximum level. The results for the pressure at the lock chamber bottom and top of the IRS can be found in Table A 25. Input ρ = 1025 kg/m 3 g = 9,81 m/s 2 h = see Table A 25 and Table A 26. Location Minimum water level [kpa] Maximum water level [kpa] Bottom lock chamber 93,7 (h = 9,32 m) 97,4 (h = 9,69 m) Top IRS 68,6 (h = 6,82 m) 72,3 (h = 7,19 m) Table A 25 Hydrostatic pressure acting on the IRS during the inflated state. Deflated phase During the deflated phase the range of water levels upon the IRS is equal to all water levels occurring in the lock chamber. These are the maximum lockage level of +3,40 m NAP and the minimum water level of -2,78 m NAP. In Table A 26 the results for the hydrostatic pressure are shown. Location Minimum water level [kpa] Maximum water level [kpa] Bottom lock chamber 46,9 (h = 4,66 m) 109,0 (h = 10,84 m) Table A 26 Hydrostatic pressure acting on the IRS during the deflated phase. 29 [L15] VNSC, Zoutgehalte, waterstand en debiet KGT , Master thesis Application of an IRS in a navigation lock

161 A7.2 LOADS CAUSED BY LOCK OPERATIONS Gate operations, levelling and flushing will lead to flows and eventually waves of translation. The flows are induced by the lift over the lock chamber. Waves of translation can occur because of the non-permanent discharge during levelling operations A7.2.1 Flows during gate operations During gate operations flows will occur through the opening between the gates. Some situations are distinguished: The lock gates are opened when the remaining head difference over the lock gates is small, for example 0,10 meter. Gate operations are executed in a small existing flow in the lock chamber. A small head difference over the gate occurs because the gates are pushing water in the direction of the movement. In the above situations water flows through the slits around the lock gates. Thin jets along the gates are occurring and these jets are quickly breaking in downstream direction. The influence area of these jets is often small, 1 or 2 times the height of the wet part of the gates. This makes that these jets are normally not governing for bottom protections and do not affect the hawser forces. For the thin jets flowing into the lock chamber the influence areas are determined with the factor 2 (governing): Influence area for the flood gates: 20,8 m (for the maximum lockage level in the WS: +3,4 m NAP). Influence area for the ebb gates: 9,5 m (for the highest water level in the GTC +2,38 m NAP). The IRS will not be located just behind a set of mitre gates. As the lock is equipped with ebb gates and flood gates, there is always a second set of mitre gates in between the gates that are opened and the IRS. This results in a space of at least the 20 meter between the operated set of gates and the IRS. Hence, the flows by gate operations will not have a large impact at the IRS and most likely never reach the IRS. A7.2.2 Jet flows caused by levelling operations The jet flows caused by levelling operations are initialized by the lift of the lock chamber and the size and amount of the openings for filling and emptying. The velocity that may happen is related to the maximum allowed hawser forces of moored vessels. The hawser forces for inland vessels are maximum 1 of the weight of the water displaced by the largest loaded vessel. For sea vessels the allowed hawser forces are much smaller, for example 0,25. A calculation sheet made by Grontmij is used for determining the size of the openings that are needed in order to limit the hawser forces. In the sheet the conditions described by the guideline Design of navigation locks 30 are programmed. It has been found that a total area of the openings of 35 m 2 is sufficient for keeping the hawser forces at an acceptable level. The width of the openings of coastal locks is usually 0,5 to 0,67 of the width of the lock chamber. With the factor 0,67 a total width of the openings of more or less 16 meter is found. Than the height of the openings is 2,2 meter in order to get a surface of the openings of at least 35 m 2. It is assumed the openings are streamlined and therefore fully effective. 30 [L10] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 2, Steffen Woudstra

162 The maximum velocity of the speed in the jet flow caused by levelling operations is than calculated by: Where: u n = The velocity just behind the opening [m/s] Q n = The maximum discharge through the openings [m 3 /s] b n = Total width of the jet flow just behind the opening [m] d n = Total height of the jet flow just behind the opening [m] It is possible to calculate the maximum discharge with the calculation program LOCKFILL. Since this would lead to a time consuming process, a safe estimation is done and checked with the experience of a specialist. The discharge is conservatively estimated by dividing the maximum volume needed for levelling by an average filling or emptying time (11 minutes). The maximum volume needed follows from the horizontal dimensions of the lock chamber and the maximum lift. The situation with the highest water level in the GTC and the lowest lockage level for the WS is governing. In that situation the maximum lift is 5,03 meter during the inflated phase and 5,16 meter in the deflated phase. A maximum volume for levelling is found with the lift of 5,16 meter and leading to a discharge of Q n of 50 m 3 /s. The velocity of the jet flow becomes u n = 1,4 m/s just behind the openings in the gates. It is important to know the velocity of the jet flow at the location of the IRS. According to the guideline Design of navigation locks, the location where the velocity at the bottom is maximum uses a line with a slope of 1:10 (5,7 ) from the centre of the jet flow. Where the line intersects the bottom the flow velocity at the bottom is maximum. The following formula is used: Where: x bn = The horizontal distance from the origin of the jet to the location at the bottom [m] e n = The height of the centre of the jet flow above the lock chamber floor [m] α = The angle of the centreline of the jet flow with the horizontal [degrees] To make things clear the above parameters are also given in Figure A 9. Figure A 9 Jet flow behind and opening in a gate ([L11] Bouwdienst Rijkswaterstaat). 148 Master thesis Application of an IRS in a navigation lock

163 It is assumed the openings in the gates start at 0,5 meter above the sill of the lock chamber. The height of the sill above the floor and half the height of the openings are added in order to find e n. For the governing situation with the highest water level in the GTC, e n becomes: Where: d n = 2,2 m h opening = 0,5 m h sill = 0,44 m e n = 2,04 m With α = 0 the distance x bn becomes 20,4 meter. The flow velocity at a distance x can be calculated by: Where: u xn = the velocity at a distance x from the origin of the jet flow [m/s] x = the horizontal distance from the origin of the jet flow [m] For the distance x = 20,4 meter a velocity of u xn = 1,0 m/s is found. The IRS will be located at least 20 meter behind the gates used for filling or emptying the lock chamber. In the governing situation the IRS is deflated and located at the bottom of the lock chamber. At a distance of 20 meter behind the gates the velocity of the jet flow is found to be 1,0 m/s at the height of the centre of the jet flow. The turbulence intensity for the jet flows occurring during filling through the gates is estimated as 0,25. The previous results for jet flows caused by levelling operations are gathered in Table A 27 Results from calculations jet flow by levelling operations. Results jet flow by levelling operations Total width openings 16 m Height openings 2,2 m Maximum discharge 50 m 3 /s Maximum velocity just behind openings 1,4 m/s Location maximum velocity at bottom 20,4 Maximum velocity at bottom 1,0 m/s Velocity 20 meter behind opening 1,0 m/s Turbulence intensity jet flow 0,25 Table A 27 Results from calculations jet flow by levelling operations. Steffen Woudstra

164 A7.2.3 Waves of translation caused by levelling operations Waves of translation can be generated in the lock chamber by the non-permanent discharge during levelling operations. These waves of translation will reflect against the gates and partly against the bows of the vessels in the lock chamber. The water surface will become in an oscillating movement in the longitudinal direction of the lock chamber 31. The oscillating movement has the eigen period of the lock chamber. The presence of vessels in the lock chamber makes the period larger. As stated before the filling and emptying system is designed such that the hawser forces are maximum 1 of the weight of the water displaced by the largest loaded vessel. Generally the slope of the water surface in the lock chamber is also not more than For the maximum slope of 1 the water pressure difference along the lock chamber can be calculated. The water pressure profile under a translation wave can be considered as hydrostatic. The amplitude of the water surface because of a translation wave can be calculated by: Where: Δh = the amplitude of the translation wave [m] γ = the slope of the water surface [-] l k = the length of the lock chamber [m] For the longest possible section of the Eastern Lock, the section between the outer flood gates, the lock chamber length is 300 meter. For a slope of 1 the amplitude becomes 0,15 meter. Along the total length of the lock chamber the water level difference is 0,3 meter, which results in a pressure difference of 3,0 kpa or 0,03 bar. The period of the translation wave for a lock chamber without vessels is calculated by: [s] Where: T k = the eigen period of the translation wave [s] c k = propagation speed of the wave, (g*d) 0,5 [m/s] d = depth of the lock chamber [m] The period for the section of 300 meter long is 89 seconds for the minimum lockage level (d = -7,44-(- 2,78) = -4,66 m). For the maximum lockage level it is 58 seconds (d = -7,44-(+3,4) = -10,84 m). For a lock chamber with vessels the period becomes larger as the velocity of the wave reduces by the blocking of the water by vessels. In the above formula the influence of the vessels can easily be added. 31 [L11] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 2, [L11] Bouwdienst Rijkswaterstaat, Ontwerp van Schutsluizen 2, Master thesis Application of an IRS in a navigation lock

165 A7.2.4 Currents caused by flushing operations According to agreements between the Dutch and Belgium governments there must be at least 100 m 3 /s flushing capacity in the Terneuzen Lock complex. At present a flushing capacity of 170 m 3 /s is present. Part of the capacity is delivered by the longitudinal culvert system of the Western Lock, which has a capacity of 35 m 3 /s. When the remaining 135 m 3 /s is equally divided over the wet cross sections of the three lock chambers, a capacity of 18 m 3 /s belongs to the Eastern Lock. The Eastern Lock is only used for flushing in highly exceptional situations. Flushing through the openings in the gates the Eastern Lock will lead to currents in the lock chamber described by: Where: u f = current by flushing [m/s] Q f = discharge by flushing [m 3 ] A lc = wet cross section of the lock chamber [m 2 ] Filling in the previously determined parameters the current by flushing becomes 0,17 m/s over the full wet cross section of the lock chamber. A7.3 EXTERNAL LOADS Several loads from outside of the lock chamber will potentially lead to a load on the IRS. A7.3.1 Wind generated waves Normally locks are protected from large wind waves by wave breakers in order to reduce hindrance by waves for vessels entering the lock. That means in regular locks the wind waves are developed in the near of the lock chamber and therefore only small. In that case a submerged rubber structure in a navigation lock will not be directly loaded by the impact of (irregular) wind waves. Wind waves in navigation locks are only relatively small compared to the depth of the lock and vertical accelerations (orbital motion) and pressure differences are not likely to have any effect on the rubber structure. A7.3.2 Long waves Long waves have periods of typically several minutes up to hours. Long waves are seiches, tsunami waves, tides and storm surges. The negligible vertical accelerations make the pressure distribution under the long waves hydrostatic. The slope of the water level for such waves is really small and on the scale of a lock chamber negligible. The influence of long waves on the hydrostatic pressure is taken into account via the minimum and maximum lockage levels. A7.3.3 Waves of translation Translation waves can be developed outside the lock chamber, for instance because of filling and emptying operations of other lock chambers, flushing, and during passage of shipping in junctions of waterways close to the navigation lock. These waves of translation can propagate into the lock chamber. Seiches in ports or other half open bays can result in waves of translation in navigation locks. Seiches are standing waves with a frequency equal to the resonance frequency of a basin and hard to predict. Previously a maximum slope for waves of translation of 1 is determined. Steffen Woudstra

166 A7.4 LOADS BY SHIP MOVEMENTS Vessels movements are leading to return currents, propeller wash, jet flows from bow thrusters, primary and secondary waves. Three governing situations are distinguished in which the design push barge is sailing: 1) The push barge is sailing in or out of the lock chamber for the smallest water level of the GTC for which the push barge may use the lock chamber (+2,13 m NAP). The IRS is deflated and the depth in the lock chamber is 9,57 meter. 2) The push barge is sailing in the lock chamber for the smallest water level of the GTC for which the push barge may use the lock chamber. The IRS is inflated and the depth in the lock chamber is 9,57 meter. 3) The push barge is sailing in the lock chamber with the lowest water level of the WS for which the push barge may use the lock chamber (-2,5 m NAP). During this water level the IRS is always deflated and the depth is 4,94 meter. A7.4.1 Return current The return current by vessels is a function of the sailing speed and the amount a vessel is blocking the waterway profile. The maximum speed with which vessels can sail is limited by the return current and squat of vessels, this the so-called limit speed. The limit speed is calculated with: Where: v l = the limit speed [m/s] A v = the wet cross section of the vessel (maximum width times maximum draught) [m 2 ] A lc = the wet cross section of the lock chamber [m 2 ] h lc = water level in the lock chamber [m NAP] z b = level of the lock chamber bottom [m NAP] g = gravitational acceleration [m/s 2 ] The larger the vessels compared to the canal profile, the smaller the limit speed. Despite of the smaller limit speed, the largest vessels gives the largest return current. The depth in the lock chamber for the three situations is: 1) z b = -7,44 m NAP and h lc = +2,13 m NAP. The depth is h 1 = 9,57 meter. 2) z b = -7,44 m NAP and h lc = +2,13 m NAP. The depth is h 2 = 9,57 meter, the depth above the inflated IRS is 7,07 meter. 3) z b = -7,44 m NAP and h lc = -2,5 m NAP. The depth is h 3 = 4,94 meter. The wet cross section of the vessel is: Where: b v = width of the vessel [m] d v = draught of the vessel [m] A v = 23*4,3 = 98,9 m Master thesis Application of an IRS in a navigation lock

167 The wet cross section for the three situations becomes A lc = (h lc -z b )*b = d*b: 1) A lc = 9,57*24 = 229,7 m 2 2) The cross section of the IRS has to be subtracted from the wet cross section of the lock chamber, the wet cross section of the IRS is estimated to be 40 m 2. A lc = 9,57*24-40 = 189,7 m 2 3) A lc = 4,94*24 = 118,6 m 2 The limit speeds for the design push barges has been determined for the three governing situations. The following limit speeds inside the lock chamber are found: 1) v l = 2,49 m/s. 2) v l = 1,82 m/s. 3) v l = 0,41 m/s. There is a large difference in the limit speeds, since the sill at the Western Scheldt side is located 4,63 meter deeper than the sill at the Gent-Terneuzen Canal side. This leads to a much smaller wet cross section of the lock chamber when the water level of the WS is present in the lock chamber. In practice the vessels will have to stop and moor in the lock chamber and therefore they will sail at a low speed. The above limit speeds is therefore unrealistic but provide a safe estimate for the return current. The return current can be calculated by: Where: u r = the return current [m/s] β = coefficient return current [-] v max = for this situation with a constant cross section A lc equal to the limit speed v l [m/s] β is equal to: 0,60 (A v /A lc =0,35) to 0,80 (A v /A lc =0,35) for v max = v l. This gives the following outcomes for β in the three governing situations: 1) β = 0,64 2) β = 0,68 3) β = 0,80 The following return currents are found: 1) u r = 1,20 m/s 2) u r =1,34 m/s 3) u r = 1,66 m/s Steffen Woudstra

168 A7.4.2 Bottom shear stress by return current The return current in the lock chamber leads to a situation where water flows along the IRS. Such a situation is known as wall flow. In a wall flow the velocity of the flow and the component of the fluid pressure on the wall lead to a shear stress at the wall. This shear stress leads to friction. For a uniform flow in an open water way the shear stress is in balance with the slope of the energy line. In formula form this is written as: Where: τ b = the bottom shear stress [N/mm 2 ] ρ = the mass density of the water, salt water with ρ = 1025 is governing [kg/m 3 ] g = gravitational acceleration [m/s] R = the hydraulic radius of the waterway [m] i = slope of the energy line in a uniform flow [-] In a uniform flow the slope of the energy line i can be calculated with: Where: L = the length of the slope [m] Δh = the vertical difference in the energy line along the slope [m] u = the velocity average over the height and time [m/s] In practice a flow is never uniform. The presence of a wall influences the flow. The region where the velocity of the flow is influenced by the wall is called boundary layer. Accelerations and decelerations influence the boundary layer and turbulence in the flow. Since the turbulent velocity profile is not known and hard to approximate, the above formulas for a uniform wall flow are used as a first estimate of the bottom shear stress. The hydraulic radius R is equal to the wet cross section of the flow divided by the wet perimeter of the lock chamber and the IRS (in inflated or deflated state). The IRS has a cross sectional area of 43,3 m 2 and a wet perimeter of 24,4 m. These values are used in the determination of the hydraulic radius. The hydraulic radius for the three situations becomes: 1) R = 5,3 m 2) R = 4,3 m 3) R = 3,5 m The slope of the energy line is calculated along the length of the push barge of 23 meter wide and with a draught of 4,3 meter. These dimensions belong to CEMT class 6a and 6b. These vessels have configurations of 1x2 barges (6a) and 2x2 barges (6b) and lengths of meter and 185 to 195 meter. The shortest length will lead to the larges slope of the energy line and therefore the largest bottom shear stress. 154 Master thesis Application of an IRS in a navigation lock

169 The slope of the energy line becomes with a length of L = 95 meter: 1) i = 0,00073 [-] 2) i = 0,00106 [-] 3) i = 0,00140 [-] All the factors needed for the calculation of the bottom shear stress are known. For the three situations the shear stress is found to be: 1) τ b = 41,4 N/m 2 2) τ b = 48,6 N/m 2 3) τ b = 52,0 N/m 2 In the Eastern Lock the IRS can have a maximum length of 140 meter because of the presence of the intermediate gates. The bottom shear stress is calculated for a push barge with a length of 95 meter. This is shorter than the IRS length. In practice the return current will be present in a longer section than only just along the vessel. The flow will continue and decrease behind the vessel. A conservative assumption is done in order to get a safe value for the friction force along the IRS by the bottom shear stress. It is assumed that the return current and the slope of the energy line will be present over the full 140 meter length of the IRS (in a later design the longest IRS is only 80 meters long). Now the following friction force per meter width of the IRS is found for a length of 140 meters: 1) T τ = 5,8 kn/m 2) T τ = 6,8 kn/m 3) T τ = 7,3 kn/m These loads are really small compared to the earlier calculated membrane force of 930 kn/m occurring for the 2D static equilibrium in the midsection of the IRS. A7.4.3 Propeller wash An estimation of the jet flow out of the propeller of the vessels is made. The vessel with the combination of the largest draught, largest propeller and engine power is governing. Therefore the largest push barge is considered for the earlier defined three governing situations. The smallest water level will result in the large flow velocity at the bottom. The manual Design of navigation locks gives properties of the propeller and engine power for several vessels. Regular push barges have propellers with a propulsion power of 1200 kw 33. For the push barge two propellers with each a propulsion power of 1200 kw and an effective diameter of D 0 = 1,60 m are usual. The following formula for the velocity of the jet flow from the propeller is used: Where: u p = the velocity just behind the propeller [m/s] P d = the engine power that is used by the propeller [kw] D 0 = the effective diameter of the propeller [m] 33 [L23] Rijkswaterstaat Dienst Verkeer en Scheepvaart, Richtlijnen Vaarwegen 2011, December Steffen Woudstra

170 For the design push barge this gives a flow velocities of u p = 8,93 m/s. The location of the maximum velocity acting at the bottom is given by: Where: x dp = the horizontal distance from the propeller to the maximum velocity at the bottom [m] d p = the vertical distance from the centre of flow to the bottom [m] The factors are also given in Figure A 10. Figure A 10 Breaking of a jet flow from a propeller ([L11] Bouwdienst Rijkswaterstaat). The vertical distance from the centre of the flow to the bottom is given by: With the parameters given before the distance d pi becomes: 1) d p1 = 6,07 m 2) d p2 = 3,57 m 3) d p3 = 1,44 m The maximum velocity at the bottom can now be calculated by: The amount of propellers is called n and the design push barge has two propellers. For the three governing situations the following locations and velocities are found: 1) x dp = 34,0 m and u bp = 1,0 m/s 2) x dp = 20,0 m and u bp =1,7 m/s 3) x dp = 8,1 m and u bp = 4,2 m/s According to the guideline Design of navigation locks the turbulence intensity for propeller flows is 0,35 to 0, Master thesis Application of an IRS in a navigation lock

171 A7.4.4 Flows caused by bow thrusters A similar approach is used for determining the flow velocity from bow thrusters. Because the thrusters are placed inside the bow, a factor is added for the energy loss in the canal system. Where: v p = the velocity of the flow just in front of the thrusters [m/s] ζ = factor for the energy loss because of the canal system of bow thrusters with sideways outflow [-] The factor ζ for regular vessels is 0,9. A flow velocity of v p = 8,04 m/s is found. For a free round jet flow the maximum velocity at the bottom is: Where: v bp2 = the maximum flow velocity at the bottom at a horizontal distance y bp2. y bp2 = the horizontal distance to the intersection of a line from the centre of the flow with a slope of 1:10 with the bottom. For the three governing situations y bp2 has been calculated with: 1) y bp2 = 60,8 m. 2) y bp2 = 35,77 m. 3) y bp2 = 14,43 m. These locations are all outside the lock chamber, and hence the maximum flow will occur at the lock chamber walls. The lock chamber walls will break the flow and this will lead to a turbulent situation. The bow thrusters flow velocity is smaller than the flow velocity of the main propellers. The bow thrusters generally have a smaller propulsion power than the main propellers. Therefore it is expected that the flow from the propeller is governing and the flow from the bow thrusters is of minor influence. During the design of the IRS it should be kept in mind that the flow from the bow thrusters occurs in another direction and can still become important. Steffen Woudstra

172 A7.4.5 Primary and secondary waves The primary wave at the bow of the vessels will first lead to an increase of the water level n 1 and then a decrease in the water level along the bow n 2, see Figure A 11. Figure A 11 Primary wave while sailing into the lock chamber ([L11] Bouwdienst Rijkswaterstaat). The increase in the water level can be calculated by: Where: n 1 = the initial wave height [m] λ 1 = coefficient water level increase primary wave [-] v si = sailing speed, the limit speeds are governing [m/s] A s = wet cross section of the vessel [m 2 ] b lc = the width of the lock chamber [m] d lc = the depth of the lock chamber [m] λ 1 has been determined for all the three governing situations from a graph. For v si the governing limit speeds are used. The other parameters are calculated before. The water level depreciation n 2 can be found in a similar way, only the coefficient λ 2 is different. For the three situations the following results have been found: 1) n 1 = 0,21 m and n 2 = 0,36 m. Together 0,57 m. 2) n 1 = 0,25 m and n 2 = 0,38 m. Together 0,63 m. 3) n 1 = 0,15 m and n 2 = 0,18 m. Together 0,33 m. The two components n 1 and n 2 will result in a quick change in the water level and hence the water pressure. For the three governing situations the water pressure change is: 1) 5,7 kpa = 0,057 bar 2) 6,3 kpa = 0,063 bar 3) 3,3 kpa = 0,033 bar The secondary waves are smaller than the primary wave and have a shorter period. Therefore the primary waves are governing. The wave heights have been calculated for a vessel sailing into the lock chamber. Vessels sailing out of the lock chamber need to make speed and therefore it is expected that they produce a smaller primary wave. 158 Master thesis Application of an IRS in a navigation lock

173 A7.5 CONCLUSION GOVERNING LOADS The hydrostatic pressure will always be present in the lock chamber. During the inflated phase the largest hydrostatic pressure is 97,4 kpa. The design of the IRS will be developed such that in all cases a static equilibrium is present for the submerged IRS. From the previous analysis of the size of the loads followed that the jet flow resulting from gate operations will not reach the IRS or only a really small flow velocity will act on the IRS. Levelling operations and flushing will only be executed when the IRS is deflated. Flow velocities up to 1,0 m/s are expected 20 meter behind the openings in the gates.. The influence of external loads is only small, or already taken into account in other load categories (hydrostatic pressure). Moving vessels are leading to locally large loads by jet flows by the vessels main propellers. Flows with velocities up to 4,2 m/s in the deflated phase and 1,7 m/s in the inflated phase can occur. Also significant return currents can happen up to 1,66 m/s during the deflated phase and 1,44 m/s during the inflated phase. The influence of the primary and secondary wave is relatively small. Flow from bow thrusters will have less impact than the flow from the main propeller since the flow of bow thrusters will not directly hit the IRS. During the inflated phase the return current will act a load in the length direction of the IRS. The friction force caused by the return current is maximum 7,3 kn/m (per meter width) of the IRS. This is small compared to the membrane force caused by the resulting pressure on the sheet. Despite of the small size of the load, the load transfer and deformation of the sheet because of the return current forms an interesting case for further studies. The jet flow from the vessels main propeller will lead to locally large velocities. During the inflated phase dynamical loads can result in a changing shape of the IRS. In a navigation lock a minimum keel clearance should always be guaranteed. During the inflated phase the IRS has stiffness and the deformation of the IRS will be limited. Hence, a minimum keel clearance can be guaranteed. During the deflated state the IRS has no stiffness and the stability of the rubber sheet loaded by the jet flow from the propeller becomes an interesting case for further studies. The jet flow velocity of 4,2 m/s is governing. Concluding the largest load is by far the hydrostatic pressure. Interesting load cases for the strength of the sheet are: Inflated phase: hydrostatic pressure + return current Deflated phase: hydrostatic pressure + propeller wash The total load by the return current and propeller wash on the IRS is only small compared by the load caused by the overpressure inside the IRS. This overpressure withstands the external hydrostatic load. At first only the hydrostatic pressure is taken into account for the first design of the IRS. After a first design is made, for a more detailed design calculations can be executed for several load cases. From these cases more specific information about load transfer and membrane forces will be gained. With these information the design can be further improved in a cyclic way. In that way a design will result that is able to withstand all load cases. Steffen Woudstra

174 Appendix 8 ALTERNATIVES LAYOUT ENDS OF THE IRS In this appendix the alternatives for the ends of the IRSs are described.the ends have been assessed for the load transfer and the space occupied by the ends. The load transfer should be such that no large stress concentrations occur and an equal distribution of the loads towards the clamp line happens. The ends should not occupy a lot of space, since the saved volume of the ends save is relatively small. A8.1.1 Alternative 1 Alternative 1 consists of a design in which the width of the sheet decreases towards the end until a width of 24 meter is reached. This equals the width of the lock chamber. The horizontal length of the slope is 10 meter. The geometry of the sheet is such that is a straight slope. Figure A 12 Overview alternative 1. Advantages: The clamping line which connects the sheet to the lock chamber consists of straight lines only and therefore is easy to construct. Disadvantages: The slope from the centre of the alternative towards the corners of the ends is small. And this slope is smaller than the slopes from the centre towards the clamp lines. Hence, the area of the sheet close to the corners will not have a large contribution to the vertical load transfer. The vertical loads will be transferred to the sides and to the middle part of the straight end. For loads in the horizontal direction stress concentrations will occur towards the corners. The end occupies a lot of space but does not have a lot of volume under the sheet. Therefore the ratio saved volume relative to the occupied space is small. This makes the end ineffective for water saving. 160 Master thesis Application of an IRS in a navigation lock

175 A8.1.2 Alternative 2 Compared to alternative 1 in this alternative the equal distribution of the loads along the clamp line is improved. The width of the sheet is decreasing faster towards the end. In such a way the end has a circular shape. The radius of the circular end in the hoop direction at bottom level is 12 meter. A straight slope is created in the centreline at the end. Figure A 13 Overview alternative 2. Advantages: A relatively equal distribution of vertical loads along the clamping line will occur. Because of the limited amount of sheet material the alternative is less sensitive for large deformations. Disadvantages: The straight shape of the sheet at the end is quite different from the shape of the sheet resulting from the hydrostatic load. This will lead to hindered deformations resulting in additional stresses in the sheet. A small ratio of the water saving relative to the occupied space. Steffen Woudstra

176 A8.1.3 Alternative 3 In alternative 3 a similar rounded end as in alternative 2 is applied. But now a larger sheet is used to construct the end. Again a radius of 12 meter is present at the level of the bottom. As a first estimate the curvature of the sheet is chosen equal to the curvature of the sheet in the midsection. Figure A 14 Overview of the rounded end of alternative 3. Advantages: The slopes perpendicular to the lines of equal height are constant. Therefore the vertical loads will be equally distributed along the rounded clamping line of the end. The horizontal loads will also be equally distributed by hoop stresses and stresses towards the clamping line. The sheet of the ends will be large enough to easily deform into a shape that is close to the shape occurring for the 3D static equilibrium. This will lead to a situation where free deformation is possible. Disadvantages: The end has a length of 12 meter and therefore occupies a lot of space. The end is more effective for water saving than the previous alternatives, but still not an optimal solution. 162 Master thesis Application of an IRS in a navigation lock

177 A8.1.4 Alternative 4 In this alternative the length of the end is only 6 meter. Compared to the other alternatives the average slope towards the end is two times steeper. The dimensions of the sheet are large enough to freely deform into an equilibrium shape for the hydrostatic load. Figure A 15 Overview alternative 4. Advantages: A relatively equal distribution of vertical loads will happen. The membrane forces will be slightly directed towards the centre. The alternative consists of a relatively small end that does not occupy a lot of space and has relatively large amount of volume under the sheet. Because of the small geometry of the sheet also the deformation of the end will be limited. Disadvantages: It is questionable wheter the ends will be able to transfer horizontal loads to the foundation without the occurance of large membrane stresses. This should be further researched with help of a 3D analysis. Steffen Woudstra