Influence of foundation model complexity on the design loads for offshore WTG on jacket foundation

The present work investigates the influence of using different ways of interfacing wind turbine model and foundation on loads in the combined structure. In the design procedure for offshore wind turbines it is common that foundation and wind turbine design loads are obtained in two sequential steps where firstly; the wind turbine designer defines the interface forces and moments in the interface point to the foundation based on either fixed or flexible boundary condition at the interface, and secondly; the foundation designer then uses those loads combined with additional wave and current forces to obtain the design loads for the foundation. The dynamic interaction between the wind turbine and foundation is left out in that procedure. Herein, three different design methodologies are applied to the same offshore wind turbine with identical turbulent wind (18 m/s) and irregular waves (Hs=6 m/Tp=10 s). The 5MW NREL reference turbine [1] on a jacket foundation from IEA Wind Task 30 OC4 [2] is used, and the differences in the design loads are compared using the aeroelastic code, HAWC2 [3].