Japan is one of the most seismically active countries in the world, and is currently planning to invest on offshore wind energy. In support of this relevant energy transition, this work presents a numerical study regarding a monopile-supported offshore wind turbine (OWT) under seismic loading conditions. For this purpose, a realistic design of an 8 MW OWT is considered, wished-in-place in a layered, non-liquefiable Japanese site. The OWT seismic response is analysed via 3D FE modelling incorporating for the soil the well-established SANISAND bounding surface plasticity model, and thus enabling realistic simulation of the cyclic hydro-mechanical response of the coarse-grained materials at the considered site. Site data regarding soil stratigraphy and past earthquake records were obtained from the well-known Japanese KiK-net database. From these data, the 15 parameters of the SANISAND model were calibrated by combining back-analysis of seismic records and available linear elastic soil properties.
The influence of different intensity earthquake records on the response of the OTW-monopile-soil system is examined both for horizontal and vertical seismic components. Even in a non-liquefiable site, pore pressure effects and their impact on the structural response are clearly visible in the simulation results. The likely coexistence of seismic and SLS wind/wave loading is also considered for completeness.