Greenup Lock Filling and Emptying System Study

Transcription

1 Fourth LACCEI International Latin American and Caribbean Conference for Engineering and Technology (LACCET 2006) Breaking Frontiers and Barriers in Engineering: Education, Research and Practice June 2006, Mayagüez, Puerto Rico. Greenup Lock Filling and Emptying System Study Mario J. Sanchez Research Hydraulic Engineer, Coastal and Hydraulics Laboratory, Engineering Research and Development Center, Vicksburg, MS, USA, Abstract The United States waterway system finds itself facing increasing commercial traffic while the system s infrastructure has essentially reached its design life. Financial constraints require innovative design concepts on infrastructure improvements. The overall savings estimated from the use of these innovative construction concepts for the US Army Corps of Engineer s top 11 high-priority navigation projects are between 1.4 and 1.8 billion dollars. The Greenup Lock in the Ohio River is one of these projects. One of the innovative designs being considered for this site is extending the lock walls of the existing m auxiliary lock and converting it into a m long lock. Two alternatives have been proposed within this lock extension project. A cost effective design alternative being considered for the filling and emptying system is the use of the existing m lock system to fill the m lock. This type of system is hydraulically unbalanced and could be prone to extremely slow filling and emptying times, and higher hawser forces. Another alternative is to build a separate filling and emptying system for the extended portion of the lock. This will provide a more balanced environment within the chamber during the filling and emptying cycles. Research on these systems has determined minimum filling and emptying times, with acceptable hawser forces, minimal surface drift, and disturbance. This paper presents the modeling methods used to establish design criteria. This criterion is necessary for design engineers investigating the m extension of the Greenup Auxiliary Lock. Keywords Navigation locks, filling and emptying systems, lock extensions, intake design 1. Introduction 1.1 Background The United States waterway system finds itself facing increasing commercial traffic while the system s infrastructure has essentially reached its design life. The result is an increased demand on the nation s navigation locks.

2 Several U.S. Army Engineer Districts are considering the use of innovative design alternatives to increase their lockage capacity. Currently, many of the dams have two locks in operation, a main and an auxiliary lock. The main lock is nominally 366 m long and the auxiliary 183 m long. The Greenup Locks and Dam are one such example. The traffic of longer tows is increasing on the Ohio River and its tributaries, and one of the innovative designs being considered by several projects is extending the lock walls of existing 183 m auxiliary locks and converting them into 366 long locks. This study evaluates the performance of the Greenup auxiliary lock after the extension with two proposed alternatives. One alternative is to keep the original filling and emptying (F&E) system while the other is adding a separate F&E system for the lock extension. 1.2 Prototype The Greenup Locks and Dam project is located on the Ohio River approximately 8.04 km below Greenup, KY (Figure 1). The project consists of a non-navigable, high-lift, gated dam, top length 392 m, including 75-m fixed weir with 68-m open crest, nine tainter gates, clear span 30.5 m between 4.3- m intermediate piers and m end piers, with a damming height m above sills, and two adjacent parallel lock chambers. The chambers are located on the left side of the Ohio River (looking downstream). The main lock chamber, located on the spillway side, has clear dimensions of 33.5 m by 366 m and the auxiliary lock chamber 33.5 m by 183 m. Figure 1. Location Map for the Greenup Locks and Dam Description of lock features and nomenclature used in this paper can be found in Engineer Manual (EM) Layout and Design of Shallow-Draft Waterways, EM Planning and Design of Navigation Locks, and EM Hydraulic Design of Navigation Locks. The existing F&E system consists of a multi-ported intake, chamber laterals, and a discharge outlet connected to a single culvert. Improvements to the project to enhance navigation include a 183 m extension to the to the auxiliary lock chamber walls. The lock will be m from pintle to pintle. Due to construction issues, while we

3 refer to the extended lock to as having a nominal length of 366 m, the actual length is 408 m. The design lift is 9.14 m, which occurs with a pool elevation of and a lower pool elevation of Purpose and Scope The purpose of this study was to evaluate the hydraulic performance of the Greenup auxiliary lock after a 183 m extension and to modify the filling and emptying system, if necessary, to provide an acceptable design. Two alternatives were proposed for this study. One alternative is to keep the original F&E system while the other includes adding a separate F&E system for the lock extension. The specific objectives of the study were to determine: a) Performance of the additional F&E System b) Filling and emptying times for various valve speeds at the design lift of 9.14 m. c) Hawser forces exerted on barges moored in the lock chamber. d) Pressures in the filling and emptying system. e) Overall system performance. A laboratory model was used to evaluate the performance of the filling and emptying system. Model studies of lock filling and emptying systems designed for barge traffic have targeted maximum hawser forces of kn as a design objective. System design and operation for new projects are optimized such that a full tow at design draft produce hawser forces of kn or less during lock operations at the design pool conditions (EM ). 2. Physical Model 2.1 Description A 1:25 model was built to reproduce the upper and lower approach, complete with dummy main lock, and the extended auxiliary lock with the intake, filling and emptying culvert and valves, and the discharge system (Figure 2). The upper approach, lower approach, lock chamber floor and walls, and the miter gates were constructed of plastic-coated plywood. The filling and emptying system, including the intake, filling and emptying culvert, and the discharge outlet were constructed of acrylic plastic and the filling and emptying valves were built from brass. Initially, the model included the extended lock chamber without an addition to the F&E system. This design is referred to as the Type 1 design. The lock extension using a separate F&E system to fill and empty the downstream end of the chamber is referred as the Type 2 design.

4 Figure 2. Model Photo Looking Downstream. The existing filling system consists of one intake located in the left guide wall (looking downstream) that contains eight ports 3.66 m high by 2.5 m wide with a intake port-to-culvert area ratio at the filling valve well of 2.7. The flow into the intake feeds a rectangular culvert that is 5.49 m high by 4.88 m wide. The culvert delivers flow to a set of laterals located in the upper part of the lock chamber floor. The laterals are centered in the original 183 m lock chamber. By extending the lock walls by 183 m nominally, the laterals remain in the upper part of the lock chamber (Type 1 design) and portrays an unbalanced filling system. The laterals also serve as the emptying system. During empty the flow exists through the laterals into a single culvert (5.49 m by 4.88 m) that carries the discharge into the lower approach. The additional filling and emptying system (Type 2) consists of an intake located behind the land side lock wall that contains four ports, which are 5.47 m high by 3.05 m with a intake port-to-culvert area ratio at the filling valve well of 4.3 (Figure 3). The flow into the intake feeds into a rectangular culvert 5.49 m high by 4.88 m wide. The supplemental culvert delivers flow to a set of laterals located in the lower part of the lock chamber floor. Figure 3. Plan view of Greenup extended lock, Type 2 design (scale 1:25). Eighteen aluminum barges, each simulating a length of m and width of m, tied together in a 3 by 6 tow arrangement, were loaded with weights to reproduce the desired 2.74-m draft.

5 2.2 Appurtenances and Instrumentation Water was supplied to the model through a circulating system. The upper and lower pools were maintained at near constant elevations during the filling and emptying operations using constant-head skimming weirs in the model head bay and tail bay. During a typical filling operation, excess flow was allowed to drain over the weirs at the beginning of the fill operation and minimal flow over the weir was maintained at the peak discharge thereby minimizing the drawdown in the upper reservoir. The opposite of this operation was performed during lock emptying. Upper and lower pool elevations were set to the desired level by adjusting the skimming weirs and reading piezometers placed in calm areas of the upper and lower pools. Water-surface elevations inside the chamber were determined from electronic pressure cells located in the middle and on each end of the lock chamber. Histories of the end-to-end watersurface differential were also recorded during filling and emptying operations. An automated data acquisition and control program was used to control valve operations and collect pressure and strain gauge data. The data were usually collected at a sampling rate of 50 Hz. Some of the hawser force and lock filling and emptying data were collected at 10 Hz. The processed data were used to reveal lock filling and emptying times, longitudinal and transverse hawser forces, and pressures downstream from the filling and emptying valves. A hawser-pull (force links) device was used to measure the longitudinal and transverse forces acting on the tow in the lock chamber during filling and emptying operations. Three such devices were used: one measured longitudinal forces and the other two measured transverse forces on the downstream and upstream ends of the tow, respectively. When the device was mounted on the tow, one end of the link was pin-connected to the tow while the other end was engaged to a fixed vertical rod. While connected to the tow, the link was free to move up and down with changes in the water-surface in the lock. 2.3 Similitude for lock models Complete similitude in a laboratory model is attained when geometric, kinematic, and dynamic similitudes are satisfied. Physical models of hydraulic structures with both internal flow (pressure flow) and external flow (free surface) typically are scaled using kinematic (Froudian) similitude at a large enough scale so that the viscous effects in the scaled model can be neglected. More than 50 model and 10 prototype studies of lock filling and emptying systems have been investigated (Pickett and Neilson 1988). The majority of these physical model studies used a scale of 1 to 25 (model to prototype). Lock model velocities scaled using kinematic similitude (model Froude number equal to prototype Froude number) in a 1:25-scale model have maximum Reynolds numbers at peak discharges on the order of 10 5 yet the corresponding prototype values are on the order of Boundary friction losses in lock culverts are empirically described using the smooth- pipe curve of the Darcy-Weisbach friction factor where the headloss is expressed as H f = f L D 2 V 2g where H f is the headloss due to boundary friction, f is the Darcy-Weisbach friction factor, L is the culvert length, and D is the culvert diameter. The Darcy-Weisbach friction factor for turbulent flow in smooth pipes is given in an implicit form (Vennard and Street 1982) 1 f = 2.0 log ( N R f )- 0.8

6 Because f decreases with increasing N R, the model is hydraulically too rough. The scaled friction losses in the model will be larger than those experienced by the prototype structure. Consequently, the scaled velocities (and discharges) in the model will be less and the scaled pressures within the culverts will be higher than those of the prototype. Low pressures were not a major concern with the Lock Research model s design; however, the lower discharges would in turn result in longer filling and emptying times in the model than the prototype will experience. Prototype filling and emptying times for similar designs will be less than those measured in a 1:25-scale lock model. This study used a 1:25-scale Froudian model in which the viscous differences were small and could be estimated based on previously reported model-to-prototype comparisons. Setting the model and prototype Froude numbers equal results in the following relations between the dimensions and hydraulic quantities: Characteristic Dimension 1 Scale Relation Model : Prototype Length L r = L 1:25 Pressure P r = L r 1:25 Area 2 A r = L r 1:625 Velocity 1/2 V r = L r 1:5 Discharge 5/2 Q r = L r 1:3, 125 Time T r = L 1/2 r 1:5 Force 3 F r = L r 1:15,625 1 Dimensions are in terms of length. These relations were used to transfer model data to prototype equivalents and vice versa. 2.4 Experimental Procedures Evaluation of the various elements of the lock system was based on data obtained during typical filling and emptying operations. Performance was based primarily on hawser forces on tows in lockage, roughness of the water surface, pressures, and time required for filling and emptying. 3. Model Experiments and Results 3.1 Filling Operations Initial model experiments were performed to evaluate the performance of the extended lock using only the existing filling system with a lift of 9.14 m and a lateral port submergence of 4.57 m. The lateral port submergence is defined as the distance from the lower pool to the top of the lateral port. Figure 4 shows typical time histories of water-surface and hawser forces during filling with a 9.14-m lift and 9-min filling valve. The maximum downstream longitudinal hawser was -105 kn and occurred between 4 and 5 min into the filling operation. The negative sign indicates the longitudinal hawser force is in the downstream direction. This exceeds the kn target for acceptable chamber operations. The time history of the longitudinal hawser force illustrates the conditions that exist with a F&E system that only fills in the upper half of the lock chamber.

7 Figure 4. Time History of Water-Surface and Hawser Forces During Filling Operation. The longitudinal hawser forces remain in the downstream direction until 10 min into the filling cycle. The maximum upstream transverse hawser forces measured during filling with a 9.14 m lift and 9-min valve were 11.6 kn to the left side (looking downstream) of the chamber and 20.5 kn to the right side of the chamber. The negative sign represents a transverse hawser force that moves the barges to the left side of the chamber. A positive transverse hawser would move the barges to the right side of the chamber. The maximum downstream hawser forces measured during filling with a 9.14 m lift and 9-min valve were 21.4 kn to the left side of the chamber and 20.5 kn to the right side of the chamber. The transverse hawser forces did not exceed the kn limit with the 9.14 m lift and 9-min filling valve. To determine the filling time required to maintain kn hawser forces or less with a 9.14 m lift, experiments were conducted with filling valve operations of 9, 15, and 20 min. The results from these experiments and the results for the type 2 design are shown in Figure 5. The longitudinal forces are significantly lower with the Type 2 design. Figure 5. Longitudinal Forces During the Filling Cycle.

8 3.2 Emptying operations Similar experiments were conducted to evaluate the performance of the lock chamber during emptying, using 1.0-, 3.0- and 5.0-min valve schedules. Figure 6 shows the longitudinal hawser forces obtained from these tests for both design types. The hawser force magnitudes were considerably lower than those measured during the filling cycle and again the type 2 design produced lower forces on the moored tow as compared to the Type 1 design. Figure 6. Longitudinal forces during the emptying cycle. 4. Summary and Conclusions Tables 1 and 2 show filling and emptying times and valve operations required to maintain hawser forces of kn or less for the different design types. The supplemental system reduced the filling time by 13 minutes and the emptying time by 9.5 minutes, improving chamber performance by a factor of 2 in both cases. Results show that using the existing lateral system for the 183-m lock to fill the 366-m extended lock will be inherently slow since the filling is being conducted from one end of the chamber. The system is unbalanced and unable to provide even flow distribution within the chamber. As shown on Table 1, a filling time of 24.1 min was required for safe operating conditions with the 9.14-m lift. Results show that by adding a separate F&E system on the downstream end of the lock chamber considerably reduces the filling and emptying times. Table 1. Acceptable operation times with 9.14-m lift Design Type Filling Operation Valve Time Filling Time (min.) (min.)

9 Table 2. Acceptable operation times with 9.14-m lift Design Type Emptying Operation Valve Time (min.) Emptying Time (min.) Acknowledgement The laboratory experiments presented in this paper were based on studies conducted by the U.S. Army Engineer Research and Development Center. Funding for the research effort was provided through the Civil Works Program of the U.S. Army Corps of Engineers. Permission has been granted by the Corps of Engineers to publish this paper. References Pickett, E. B., and Neilson, F. M. (1988). Lock hydraulic system model and prototype study data, Miscellaneous Paper Hl-88-1, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS U.S. Army Corps of Engineers (1995). EM , Planning and design of navigation locks. U.S. Army Corps of Engineers (1995). EM , Hydraulic design of navigation locks. U.S. Army Corps of Engineers (1995). EM , Layout and Design of Shallow-Draft Waterways, Vennard, J. K. and Street, R. L. (1982). Elementary Fluid Mechanics, 6 th edition, John Wiley and Sons, New York.