DESIGNING OF THE OFFSHORE WIND FARM INSTALLATION VESSELS (on basis of the VIDAR project) Presented by: Tomasz Płotka - StoGda
0. StoGda Ship Design & Engineering Ltd Beginning of the StoGda Ship Design & Engineering it is march 1997, when Gdansk Shipyard was closed because of financial problems. Only 15 experienced designers were employed, this time. We have abt. 60 workstations now. During these sixteen years we engineered projects for our customers from all around the world from China customers, through European customers to USA/Canadian customers. Also, type of designed vessels and scope of projects were different. The next slides show our the most important projects. Maria S. Merian Icegoing Research Vessel project for German Shipyard (partly basic design and workshop docs)
Rescue Vessel project for customer from Nederland (workshop docs)
Transhipper basic design and workshop docs; built by Remontowa Shipyard,
Lengthening of the passenger vessel Braemar basic and workshop docs; for German customer
Lengthening of the passenger vessel Braemar basic and workshop docs; for German customer
When we are talking about renewal sources of energy, I should not forgot the project engineered for ODYS Shipyard (from Gdansk). It was electric power station where see waves are sources of energy. We engineered basic design and workshop docs for steel structure and piping. It was working model, in scale 1:2 for testing purposes, built for Danish contractor
1. Wind Farm Installation Vessels StoGda s Beginnings Project THOR it was our first project of the Self Elevating Wind Turbine Installation Vessels. Originally, we signed contract with Skaramanga Shipyard from Thyssenkrupp Company. Finally, this vessel was built by CRIST Shipyard. We engineered workshop docs for the hull structure and hull steel outfitting, firstly for Skaramanga, then for CRIST. Contract between CRIST Shipyard and HOCHTIEF Solutions AG.
Next one, it was INNOVATION project. We were involved much more deeper into this project. It was necessary to modify the basic design and then to engineer the workshop docs, not only hull but also deck steel outfitting, machinery piping and hull piping plus As Built docs together with naval calculations (intact stability and damage stability). Also contract between CRIST Shipyard and HOCHTIEF Solutions AG.
And finally, the latest and the newest project VIDAR project. This is fully our, StoGda s design from conceptual design, through basic design till workshop docs. It is also contract between CRIST Shipyard and HOCHTIEF Solutions AG. On basis of this project, I ll try to familiar You with designing process of the Self Elevating Wind Turbine Installation Vessels. The below presented analysis is from technical point of view, not from economical point of view.
2. Designing of the Self Elevating Wind Turbine Installation Vessels - Basics First step: to define the wind mill farms on which the vessel will operate. It allows to define the environmental conditions for operating the vessel. Chosen parameters are important because of future operation of the vessel how many days per year, the vessel will operate on the wind mill farm Please observe parameters defined on the very early stage of the project VIDAR: Transit Design Condition: Significant wave height: Wave peak period: Wind velocity: No crane operations. Jacking Design Condition and DP-2: Significant wave height: Wave peak period: Wind velocity: Current velocity: No crane operations. Water depth: Jacked Operational Design Condition: Significant wave height: Wave peak period: Wind velocity: Current velocity: Air gap at water depth xx Leg penetration With crane operations. Jacked Survival Design Condition: Maximum Water Depth Significant wave height: Maximum wave height: Wave peak period: Wind velocity: Air gap at water depth xx Current velocity: No crane operations
Second step: Speed of jacking system important factor for the staying of the self elevating unit on one place. Third step: prognosis for the wind mill farm and wind turbines dimensions of the turbines, value of the future power generation. Fourth step: payload load mass of the cargo on the main deck which vessel should be able to jack up together with selfweight. Fifth step: choosing of the SWL of the main crane and auxiliary cranes. Now we are ready for choosing the main dimensions of the vessel: Length over all Length between perpendiculars Breadth moulded Depth to main deck Design draught Scantling draught Leg length (from ship s basic line to the top of the leg) Design speed
3. Designing of the Self Elevating Wind Turbine Installation Vessels Design Challenge 3.1 Design Speed CFD calculations One of contractual value is speed of the vessel. It should be very carefully evaluated the hull form, position of the aft thrusters. The breadth of the Self Elevating Wind Turbine Installation Vessels is normally bigger than classic vessel, so the resistance of the hull is bigger. It should be checked and predicted, on very early stage of the vessel, by computational propulsion prediction, the required power of the aft thruster. Result of such calculations is shown on the diagram
3.2 Dynamic Positioning Ability Please observe this slide there is not so lot of free space for mounting the wind mills, on the wind mill farm. So, very important for the vessel, we are analyzing, is to keep position during jacking-up operation especially during first step of jacking operation, when the legs starting touch the bottom. Such ability should be checked at the early stage of the project. It is also important to minimize the power of generating sets mounted on board. Dynamic Positioning Ability is calculated at the beginning of the project and checked during tank tests. Let s observe the following slides.
Electric Load Balance prior to DP capability tank tests Electric Load Balance after DP capability tank tests
As result of the DP Capability tank test, we are receiving the following plots proving us that thruster system was properly chosen
Let s return to the slide showing the wind mill farm. Please observe, how important is Dynamic Positioning Ability. It is calm water, but normal situation is that there is wind, wave, current. It is not possible to rotate the vessel to minimize the forces acting on it (forces from wave, wind and current) because of low space between wind mills and infrastructure laying on the see bottom (cables, connection boxes). So, the vessel should keep position in case the environmental forces acting from any direction.
3.3 Green Water Wind Mill Parks are situated on the shallow water, often close to Nature 2000 areas. It means that we should save Nature and, for example, to reduce the Green Water effect. To minimize the value of the water entering the fore parts of the vessel, it should be very carefully designed the bow form and the tank rest should be done. Green Water Effect basic form of the hull
Green Water Effect final form of the hull
3.4 Air Suction by the Bow Thruster As the wind mill parks are situated on the shallow water and because of it the design draught is rather small, it can happen that bow thruster will suck the air as it is shown on the slide. Such effect can be observe during tank tests and any corrections can be made together with bow thruster supplier.
3.5 Cooling system during Jacked-up operations It is not so easy to say which cooling system, during Jacked-up operation, is better: - water cooling using raw water pumps minus is that this system is used on the shallow water and the raw water pumps will pump a lot mud together with water. It is necessary to clean, very often, the cooling water filters not so convenient. - Air cooling system - minus is that this system is not so effective as water system; additionally, the air coolers should be mounted on the deck area where is cargo area lost of cargo area.
3.6 Jacking system Type of the Jacking system was requested by Hochtief. System was designed by StoGda, excluding the hydraulic which was designed and delivered by supplier from Nederland Lifting speed for project VIDAR is abt. 1m/min and comparing with similar project, it is rather high.
To secure the smooth continuous lifting and lowering operations, two moveable rings were provided, powered by set of hydraulic cylinders. Please observe, that lifting capacity should be defined on very early stage of the project and it is not so easy to do it. Calculating it (or estimating it), not only Deadweight and mass of the empty vessel should be taken into account. Influence of the environmental forces (forces from wave, wind and current) plus gaps between sliding elements, because of friction forces, should be considered.
4. Designing of the Self Elevating Wind Turbine Installation Vessels Strength Calculations This type of vessel are treated by classification societies partly as ocean going vessels and partly as offshore structure this requires very complicated and time consuming strength calculations. The most consuming calculations are calculations of the environmental forces (forces from wind, wave and current) for several operating conditions. Please observe that there are quite good mathematical models of the wind, wave and current for the deep water.
There no exist the numerical models, enough exact, describing wave, wind and current for shallow waters areas. It is why, there is a lot of discussions between class societies and designers if the model is correct or no, what kind of factors should be taken for consideration. (for example simultaneous acting of the max wind, wave and current forces) or what kind of software is the most appropriate. According to my opinion, numerical calculations should be proved by appropriate tank tests. I have to underline, that complete tank tests, including test in wind tunnel, for the project VIDAR were performed in CTO Towing Tank, here in Gdansk.
Fatigue analysis On the right is shown example of the Operating Pattern of the Self Elevating Wind Turbine Installation Vessel. As it was said previously, some parts of the structure are treated as offshore structure and it is reason that fatigue analysis is required at least, as minimum, for offshore structure and for jacking system and structure. It is also time consuming process
5. Designing of the Self Elevating Wind Turbine Installation Vessels Vessel on the Wind Mill Farm The slide shows one of the Load Case foreseen as possible during vessel operation. Handing of the vessel to the Owner doesn t mean finish of the design work. Of course, the design work, belongs to this stage can be done by other design office but we also offer supporting Owner on this stage. Prior to leaving the harbor, each load case should be recalculated it should be calculated/checked: - Fastening of the cargo - Stability of the vessel - Longitudinal strength of vessel
The mentioned calculations should be done for each condition: - transit to wind mill farm - transit inside the wind mill farm - preloading - jacked-up operation - survival It is also must to check the see bottom and to prepare it to avoid accidence like: - punch through - bottom scour - bottom layer sliding (layered soils) - sliding - leg bottom impact
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