OFFSHORE DEPLOYMENT AND MARINE OPERATION FOR OFFSHORE WIND TURBINES. NORCOWE WP3 Meeting on 7 th June, 2010

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1 OFFSHORE DEPLOYMENT AND MARINE OPERATION FOR OFFSHORE WIND TURBINES NORCOWE WP3 Meeting on 7 th June, 2010 Arunjyoti Sarkar PhD Student (started on 02/04/2010), UIS Prof. Ove T. Gudmestad PhD Advisor, UiS

2 Offshore wind turbine for the future In recent time, lot of focus is placed on Offshore Wind Turbines for both shallow and deep waters. Sharp growth in the coming future can be seen for wind turbines in shallow to intermediate water depths for which the technology is field proven. Lesson learnt : Installation of wind turbines is the bottleneck of the existing technology. Installation : how to transport the structures, installation vessels, operation duration, allowable seastate Research focus: reduction of overall installation time and waiting for the weather window

3 Very brief on relation of installation concept to structure concept, estimation of time needed Site data (water depth, extreme loads etc) Installation concept 1. How many separate activities? 2. What type of vessel to be used for installation Conceptual design Structural design 1. ULS design, e.g. breaking waves 2. Long term behavior (fatigue, foundation, scour etc) 1. Time for each individual installation 2. Time to transfer installation vessel from one to another location (Lifting analysis) 1. Weight, dimension of structure 2. Carrying concept (floating + towing or carry on barge) Time for carrying to the site (tow analysis) Research focus: consider installation aspect and suggest modification on the structural concept. All modifications need verification following the general requirement of the structure.

4 Offshore wind turbines for shallow to intermediate water depth General components of a wind turbine : 1. Foundation 2. Supporting column 3. Nacelle 4. Blades The installation is carried out in the above sequence. The foundation structures are 1. Pile supported monopile, jacket, tripod, tripile (BARD concept) type of structures etc 2. Gravity based concrete gravity foundation For shallow water turbines, monopiles are the most preferred foundation structures.

5 Offshore wind turbine installation Important point : less number of components can reduce the individual installation time. A fully integrated structure may decrease the installation time and cost. Research focus: to develop optimized integration concept for easy installation and reduced overall operation duration. (Experience from O&G industry may be useful).

6 Offshore wind turbine installation Weather window : Experience from Oil and Gas industry: at least Hs2.0m is required as the allowable seastate for doing the installation in economic way in North sea. Common practice : carry the components in barge and install using a jack-up vessel. For most of the jack-up vessels, the operating seastate is Hs 1.5m. Important point : low operating weather window increases the overall installation time. Research focus: to develop technology that will use minimum size floating vessels to perform the same marine operations.

7 Offshore wind turbine installation - piles An observation : A floating vessel with 6 rigid body DOF is considered not suitable for operations which are motion sensitive (e.g., pile driving). But motion heave compensators (HC) fitted on the vessel may be used for such operations. Research focus: Analyze suitability of using floating vessels fitted with DP and HC system.

8 Offshore wind turbine installation - piles Research focus: Develop technology to isolate vessel motion and the pile driving operation so that the operation may be performed at higher seastate from a floating vessel as compared to present status. The sheltered area beside a vessel provides advantage for easier splash zone deployment of subsea structures.

9 Offshore wind turbine installation - piles Monopiles (for shallow water) are the best option for their structural simplicity and simple installation concept. But they are not preferred for deeper water since the natural frequency gets close to the rotor frequency (1 or 3 times). The long term scouring due to plastic deformations of the soil surrounding a monopile can also limit its application for deeper water. Research focus: To develop modified concept to the monopile structure which could be attractive solution for intermediate water depth in terms of (1) stress on soil and (2) easy installation.

10 Research Focus: Self buoyant foundations or structures fitted with external buoyancy chambers can make the floating and towing of a train of structures an attractive solution. Offshore wind turbine foundation installation - towing General method of taking the turbine foundations to the site is to carry them on a barge

11 Offshore wind turbine installation - towing Advantages of monopile floating + towing : Required crane capacity is less. Easy to upend. Research focus: to develop methodology and analyze towing of a train of floating structures to the site

12 Offshore wind turbine installation An observation : It may be beneficial to get only the generator part (including yaw mechanism) as a single unit from the turbine manufacturers. Research focus : To optimize the supporting structure (column and foundation) as a combined unit considering the installation aspect.

13 Deep water wind turbines The promising solution for floating wind turbine is the ballast stabilized structures which normally has long hulls and is thus limiting to relatively deep water. Research focus: To study the stability of floating structures during towing. If they need external buoyancy chambers while towing. To develop new floating structural concepts which may be suitable for quick installation.

14 Thank you