Fully coupled analysis of a floating offshore wind turbine under wind and wave loading

Abstract

Floating Offshore Wind Turbines (FOWTs) have been exposed to a multi-hazard scenario of wind and wave conditions, which have acted simultaneously. To assess their combined effect on the FOWT and to ensure the safety and stability of the supporting structure, numerous complex loading conditions, such as wind-induced aerodynamic loads, wave-induced hydrodynamic loads, and the dynamics of the supporting structure, have been considered. In this study, a comprehensive time-domain analysis of the NREL 5 MW Reference Wind Turbine (RWT) supported on the OC4 DeepCwind semi-submersible has been carried out under both operating and parked conditions using the aero-hydroservo-elastic tool OpenFAST. The operating condition of the FOWT has included simulations at various wind speeds from cut-in to cut-out wind speed, with co-existing wave parameters for each wind speed. Based on the fully coupled analysis of the FOWT under simultaneously acting wind and wave conditions, the principal parameters required for the structural design of the rotor and supporting structure, such as blade-root moments and tower fore-aft/overturning moments, have been presented, alongside the key aspects of environment-structure interactions.