Impact of wind-wave misalignment on the motion and wake dynamics of a 15-MW floating wind turbine

Abstract The instantaneous response of floating offshore wind turbines is sensitive to the relative direction of the wind and waves, thus their misalignment can lead to an unsteady dynamic behaviour of the system. This is analysed using a novel two-way coupled modelling approach in which aerodynamic loads are resolved using Large-Eddy Simulation (LES) coupled to a hydrodynamic rigid-body motion solver that accounts for both platform and mooring dynamics. A single IEA 15-MW turbine mounted on the Volturn semi-submersible platform with quasi-static catenary moorings operating at maximum thrust is considered. Simulations consider two wind headings (0° and 30°) in conventionally-neutral atmospheric boundary layer conditions and five wave headings (0° to 90°) with unidirectional regular waves. Results show that wind–wave misalignment affects platform motion responses and instantaneous blade loading, in particular surge and pitch motions are reduced and roll and sway markedly increased for wind heading of 30° . Maximum accelerations seen at the hub are observed in the 30° wind heading cases, especially at 30° and 60° wave heading, with the y components dominating. Wake analysis indicates that the mean stream-wise velocity deficit is largely unaffected by wind–wave misalignment across the downstream locations considered. In contrast, the near-wake turbulent kinetic energy (TKE) displays noticeable asymmetries for the floating configuration, particularly under oblique wind conditions, when compared to a fixed-bottom reference case. These effects are attributed to amplified platform-induced lateral motions due to oblique wind, which impacts the production and transport of TKE. The results highlight that fully coupled high-fidelity simulations are an essential tool for analysing unsteady response, loading and wakes of floating wind turbines under realistic environmental conditions.