The offshore wind industry is increasingly moving towards larger turbines. The growth in rotor size and aerodynamic loads necessitates larger monopile foundations. This increased foundation height results in a monopile that exhibits pronounced slenderness and flexibility. Consequently, the fixed-bottom monopile becomes more susceptible to wave loads, which can induce nonlinear vibrations in complex wave environments. Extensive physical model experiments have been conducted in a wave tank to study the nonlinear vibration characteristics of a fixed-bottom monopile under regular wave action. The experimental results demonstrate that when the wave period is close to twice the resonant period of the model, the vibration response of the monopile increases significantly. Under these conditions, a second harmonic resonance occurs, with the amplitude of the second harmonic component being more than twice that of the fundamental (wave frequency) component. Additionally, the maximum run-up around the model exhibits a W-shaped distribution in the circumferential direction, with the highest run-up observed on the incident wave side. The wave pressure at the water surface is the greatest and increases with wave height, while the pressure below the water surface gradually increases with the measurement height.

As offshore wind development moves toward deeper waters, floating offshore wind turbines have become essential for carbon-neutral energy systems. This study experimentally investigates the hydrodynamic coefficients of typical column–heave-plate components under forced oscillations, focusing on the influence of pitch-induced inclination. A circular column without a heave plate and a circular column equipped with a hexagonal heave plate were tested under heave and surge motions with varying periods, amplitudes, and static inclination angles. The static inclinations were used to represent the attitude variation of platform components during large-amplitude pitch responses. Added mass and damping coefficients were identified using the least squares method. The results show that for the heave-plate-equipped column, increasing the inclination from 0° to 5° and 10° reduced the nondimensional heave added mass by approximately 4.3% and 5.9%, respectively, and reduced the nondimensional heave damping by approximately 7.1% and 6.8%. The corresponding reductions in surge added mass were approximately 5.3% and 10.5%, whereas the reductions in surge damping reached approximately 8.2% and 16.4%, indicating that the surge damping is most sensitive to static inclination. These variations may be associated with the altered geometric projection and disturbed flow symmetry of the inclined component, which may affect the attached-fluid volume and energy-dissipation process during forced oscillation. Future studies should further verify the corresponding local separation and vortex-formation mechanisms through detailed flow-field measurements, PIV, or CFD.