Seismic response of monopile offshore wind turbines in liquefiable sand considering vertical ground motion

Offshore wind turbines experience environmental loads such as winds and waves throughout their operational lifespan, as well as accidental earthquakes in earthquake-prone regions. Earthquakes typically include high-frequency components in the vertical direction, which can be close to the natural frequency of offshore wind turbines. This study aims to assess the impact of the vertical seismic component on the dynamic response of monopile offshore wind turbines. A three-dimensional fully coupled finite element model is developed to realistically consider the dynamic interaction between the actual site and the structure. The method for simulating the interaction between water and soil is incorporated into the numerical model. Stochastic theory is utilized to simulate wind and wave. The model's accuracy is validated by comparing numerical predictions with centrifuge experimental results. The results of the parameters analysis indicate that the vertical seismic component significantly impacts the seismic response of offshore wind turbines and induces complex nonlinear behavior in sandy soil.