With the increasing construction of large-scale wind turbines in seismically active coastal areas, the survivability of these high-rated-power offshore wind turbines (OWTs) in marine and geological conditions becomes extremely important. Although research on the dynamic behaviors of OWTs under earthquakes has been conducted with consideration of the soil-structure interaction, the attention paid to the impact of earthquake-induced seabed liquefaction on OWTs supported by large-diameter monopiles remains limited. In view of this research gap, this study carries out dynamic analyses of a 10 MW OWT under combined wind, wave, and earthquake loadings. This study uses a pressure-dependent multisurface elastoplastic constitutive model to simulate the soil liquefaction phenomenon. The results indicate that the motion of the large-diameter monopile leads to more extensive soil liquefaction surrounding the monopile, specifically in the zone near the pile toe. Moreover, compared with earthquake loading alone, liquefaction becomes more severe under the coupled wind and earthquake loadings. Accordingly, the dynamic responses of the OWT are apparently amplified, which demonstrates the importance of considering the coupling loadings. Compared with wind loading, the effect of wave loading on the dynamic response and liquefaction potential is relatively insignificant.

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Summary Modern offshore wind turbines (OWTs) are constructed with increasingly long blades and slender towers to capture wind resources more effectively. Consequently, OWTs have become vulnerable to wind and sea wave excitations. Mitigations of unfavorable OWT vibrations have been extensively investigated, with the majority focusing on passive vibration control strategies with control performance sensitive to structural frequency changes. Nonlinear energy sinks (NESs) are regarded as effective vibration control methods because their broadband fashion is robust against variations in structural frequencies. A novel NES with an improved track profile that combines both second‐ and fourth‐order polynomials (Track II NES) is proposed in the present study to improve the vibration mitigation effectiveness of traditional Track I NES with a track profile of a fourth‐order polynomial only. Governing equations of a single‐degree‐of‐freedom system with Track II NES are first established, and an equivalent linearization method is adopted to optimize the track profile and damping of the Track II NES. Moreover, a detailed 3D finite element model of a representative 5‐MW OWT is developed. Control effectiveness of the Track II NES is examined under different structural stiffnesses and mean wind speeds and then compared with that of conventional tuned mass damper (TMD) and Track I NES. Numerical results showed that the Track II NES can effectively suppress displacement and acceleration responses of OWTs and outperform its counterpart Track I NES. Moreover, the Track II NES can obtain reduction ratios close to those of the TMD but with better robustness against the detuning effect.

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