Are passive vibration mitigation devices for 15+ MW offshore wind turbines still feasible?

The design of monopiles for offshore wind turbines is driven by the fatigue limit state; the wave frequency being typically almost in resonance with the first natural frequency of the turbine. While in operating conditions the oscillations induced by wave loading in fore-aft direction are typically well damped by aerodynamic damping, the excitation of vibrations in side-side direction or during standstill can lead to larger fatigue loads and thus a reduced lifetime of the substructure. Offshore wind turbines are thus often equipped with passive vibration mitigation devices, such as tuned mass dampers or slosh dampers, to reduce these otherwise low damped vibrations. As part of the project FOOS, the feasibility and performance of these passive vibration mitigation devices for offshore wind turbines in the 15+ MW range are to be investigated with a special focus on the upcoming Princess Elisabeth Zone in the Belgian North Sea. In this contribution, the technical feasibility of passive vibration mitigation devices will be evaluated for 15+ MW offshore wind turbines. An overview of common vibration mitigation devices used for offshore wind turbines will be given. Conceptual designs for these common devices, for example tuned mass dampers or slosh dampers, will be developed based on the IEA 15 MW and IEA 22 MW reference wind turbines to provide an estimation of the required masses and sizes. Based on the conceptual designs the technical feasibility will be evaluated.