The VolturnUS-S 15 MW floating offshore wind turbine under wind-wave-yaw misalignment conditions

This study investigates the effects of wind–wave misalignment, yaw (wind–nacelle) misalignment, and second-order wave loading on the dynamic response of the VolturnUS-S floating offshore wind turbine (FOWT), using the fully coupled, aero-hydro-servo-elastic simulator OpenFAST. Operational and extreme (parked rotor) environmental conditions are examined including aligned wind–wave loading, wind–wave misalignment with and without yaw misalignment, second-order wave kinematics, and a 50-year extreme sea state. Under aligned wind–wave conditions, increasing yaw misalignment amplifies sway and roll motions while reducing surge and pitch. When wind–wave misalignment is combined with yaw misalignment, sway and roll increase, while surge and pitch decrease. When the wind is misaligned with the platform but aligned with the rotor, surge, sway, and pitch increase substantially. Second-order wave loading amplifies surge and heave but does not change the overall platform-response behaviour. Spectral analysis shows that low-frequency vibrations are dominated by rigid-body platform motion, while higher-frequency rotor-support response is governed by rotor harmonics, tower flexibility, and rotor–tower coupling. Yaw misalignment redirects excitation from the fore–aft to the lateral direction, strengthening the combined fore–aft and side-to-side response. These findings highlight the importance of including aerodynamic loading directionality, with respect to the platform and nacelle, and non-linear wave hydrodynamics in FOWTs’ performance assessment.