On Modeling Coupled Influences of Wind, Wave, and Current Loads on an Offshore Wind Turbine during a Hurricane

We present simulation-based studies aimed at assessing the response of bottom-supported offshore wind turbines to physics-based offshore environmental conditions during a hurricane. The response of a parked wind turbine is studied for a hurricane scenario simulated using a fully coupled atmospheric-wave-ocean model. Based on hurricane intensity and sea severity levels generated for a simulated hurricane track, coupled turbulent wind and wave fields are developed for two offshore turbine sites located, in 20 meters of water, to the right and left side of the track through the evolution of the hurricane. Extreme rotor, tower, and support structure loads for the selected monopile-supported 5-MW offshore wind turbine are assessed for different turbine control strategies, wave kinematics assumptions, and downscaled turbulence resolution approaches. The coupled wind-wave inputs for the analysis are outputs from the University of Miami Coupled Model (UMCM). From a 1.3-km spatial resolution for the wind field, appropriate downscaling to 10-m resolution is undertaken by a stochastic approach to describe turbulence. For the waves, fully directional seas with first- and second-order kinematics are employed to generate hydrodynamic loads. Together with the aerodynamic loading, the open-source software, FAST, with enhancements included to allow new capabilities especially in the wave modeling, turbine load extremes are assessed as Hurricane Ike evolves over 120 hours.