Seismic dynamics of offshore wind turbine-seabed foundation: Insights from a numerical study

In the past 10 years, the offshore wind energy harvest industry has developed rapidly worldwide. However, seismic waves would bring a great threat to the safety and stability of offshore wind turbines (OWTs). In this study, taking the marine geotechnics numerical software FssiCAS as the computational platform, adopting the generalized elastoplastic soil model Pastor-Zienkiewicz-Mark III (PZIII) to describe the complex mechanical behavior of seabed soil, the seismic dynamics, as well as the stability of a thin-walled monopile OWT with an equipped capacity of 1.5 MW and its seabed foundation are comprehensively investigated, by the way of finely modeling and meshing for the important components of the OWT, i.e., the blades, nacelle, and tower. The numerical results indicate that OWT and its seabed foundation strongly respond to the excitation of seismic waves, and there is intensive interaction between OWT and its seabed foundation. In the case of this study, the horizontal oscillation amplitude at the top of the turbine tower reaches 2m, the superficial seabed soil at the far field is liquefied with a depth of 3-4 m, and the liquefaction depth of the seabed soil surrounding the monopile reaches 5-6 m. Even so, the OWT involved in this study has no cumulative displacement, there is only vibration displacement. It is indicated that the OWT has good seismic stability. It is indicated by the comparative study that the complex mechanical behavior of seabed soil, the complex geometry and mass distribution of OWTs, and the consideration of the pore water in seabed foundations have a radical influence on the seismic dynamics of OWTs. The work presented could be a valuable reference for the evaluation of the seismic dynamics and stability of OWTs in the future.