Dynamic response of floating offshore wind turbine to focused wave excitation

This study presents a detailed numerical investigation of a floating offshore wind turbine (FOWT) subjected to focused wave excitation, utilizing a high-fidelity, fully coupled aero-hydro-mooring computational fluid dynamics model implemented in OpenFOAM. The analysis focuses on the National Renewable Energy Laboratory 5-MW reference turbine mounted on a semi-submersible platform. The influence of wave focus positions, located upstream (FP-US), at the mid-position (FP-M), and downstream (FP-DS), is systematically evaluated in terms of platform motions, mooring line tensions, aerodynamic loading, and wake recovery behavior. Time–frequency spectrograms are employed to characterize the non-stationary and transient responses induced by the focused wave conditions. The results indicate that pitch motions are significantly amplified in the FP-US and FP-M cases compared to FP-DS, with strong pitch and surge coupling observed. Surge motions are also more pronounced in FP-US and FP-M, where low-frequency components corresponding to the natural surge frequency contribute to prolonged dynamic responses. Mooring line tensions follow a similar trend, with substantially higher loads in FP-US and FP-M due to intensified wave-induced excitation. Additionally, FP-US and FP-M demonstrate improved aerodynamic performance and wake recovery, although accompanied by increased aerodynamic fluctuations resulting from platform motions. These findings indicate the importance of accounting for wave focus positions to improve the FOWT design and performance, especially for long-term stability and efficiency.