1. Integrated Dynamic Analysis of Floating Offshore Wind Turbines EWEC2007 Milan, Italy 7-10 May 2007 B. Skaare 1, T. D. Hanson 1, F.G. Nielsen 1, R. Yttervik 1, A.M. Hansen 2, K. Thomsen 23, T. J. Larsen 2 1) Norsk Hydro O&E Research Centre 2) Risø National Laboratory 3) Presently: Siemens Wind Power Presented by: Finn Gunnar Nielsen

2. Page: 2 Background Hywind Deep-water floating offshore wind turbine Case studied: Turbine power : 5 MW Draft hull : 120 m Nacelle height : 81 m Rotor diameter : 123 m Water depth : 200–700 m Displacement : 8100 t Mooring : 3 lines Challenge existing solutions by combining technologies: Offshore floater technology from O&G industry. Best available offshore wind turbines.

3. Page: 3 Hywind technical development Theory and computer codes. Engineering studies. Production and installation studies. Model test for verification. Next step: - Full scale demo version.

4. Page: 4 Power curve Simplified wind turbine model. Maximum Power Constant Power

5. Page: 5 Thrust curve Simplified wind turbine model. Maximum Power Constant Power Negative slope => Negative damping contribution

6. Page: 6 SIMO/RIFLEX/HAWC2 Integration HAWC2 (RISØ) Wind turbine loads and dynamics Interface SIMO / RIFLEX (MARINTEK) SIMO: Rigid body dynamics in waves and current. RIFLEX: Slender flexible body dynamics in waves and current

7. Page: 7 SIMO/RIFLEX/HAWC2 Integration Testing Comparison of motions in the coupling node in simulations with SIMO/RIFLEX/HAWC2 (a) and SIMO/RIFLEX (b). Waves: Hs = 5 m, Tp = 12 s, 50 deg offset angle relative to the x-axis. No wind

8. Page: 8 HYWIND Model Scale Experiments Motivation: Validate results from numerical analysis. Demonstrate system behaviour Included: Wind, waves Mooring Various control algorithms for rotor speed and blade pitch control Scale: 1/47

9. Page: 9 Recalculations of Model Scale Experiments Used SIMO / RIFLEX / HAWC2 Implemented model test data for: - Mean wind speed and turbulence intensity - Wave spectrum - Floater and mooring model - Aerodynamic model (NACA44XX blade profile) - Control strategies

10. Page: 10 Control Strategies Estimated relative wind velocity was obtained from thrust force measurements. Rotor speed and blade pitch angle of the turbine was controlled: - Below rated wind speed: - Control for maximum possible power (variable rotor speed, constant blade pitch angle) - Above rated wind speed: - ”Conventional control” - Control for constant power (Constant rotor speed, variable blade pitch angle) - ”Conventional control with active damping” - Control for constant power and tower pitch damping. (Constant rotor speed, variable blade pitch angle)

11. Page: 11 Estimation of Relative Wind Speed quasistatic assumption The relative wind velocity is given from where is the rotor thrust force is the density of air D is the rotor diameter is the rotor speed in RPM J is the “advance number” given by the surface in the figure (1) (2)

12. Page: 12 Estimation of Relative Wind Speed Example of estimated wind speed for simulation a test : H s =9m, T p =13s, U mean =19.49m/s, T int =0.1265.

13. Page: 13 Recalculations of Model Scale Experiments free decay tests Conventional Control Constant wind 17 m/s. No waves. Conventional Control + Active Damping Constant wind 17 m/s. No waves.

14. Page: 14 Recalculations of Model Scale Experiments irregular wave tests. Conventional Control Mean wind 17 m/s. H s =5m. T p =12s Conventional Control + Active Damping Mean wind 17 m/s. H s = 5m. T p =12s

15. Page: 15 Summary and conclusions A system for integrated analysis of floating offshore wind turbines has been developed The Floating offshore wind turbine HYWIND has been model tested with control of rotor speed and blade pitch angle. The integrated computer program RIFLEX /SIMO /HAWC2 has been validated towards the model test results. - Very good correspondence between experimental and numerical results are obtained. - The negative damping of the platform pitch motion at above rated wind speeds is efficiently compensated by use of an active damping algorithm. The integrated computer tool will be applied in further optimization of HYWIND

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