Aero-hydroelastic Instabilities on an Offshore Fixed-Bottom Wind Turbine in Severe Sea State

Hydrodynamic loads associated with nonlinear wave kinematics have important effects on the structural behaviour of offshore wind turbines. Recent literature has shown that steep non-breaking waves are responsible for triggering resonant vibrations of the tower with significant implications in terms of structural safety. In this paper, a new fast hydrodynamic solver, which combines a linear and a fully nonlinear high-order boundary-element wave solver within a domain decomposition strategy, is integrated into a full hydro-aero-elastic algorithm in order to assess the effects of nonlinear contributions on the whole system, including the rotor blades. High-frequency blades oscillations caused by the wave impacts produce high-frequency load cycles in the tower loads, revealing a complete hydro-elastic coupling of the whole system. Standard linear wave theory leads to dangerous inaccuracies, not only in the tower but also in the blades responses.