Seismic Response of Spar Floating Offshore Wind Turbine

The future of the offshore wind market is looking forward to floating foundations as they are more promising in deep waters. Seismicity is a concern along the offshores of the Western United States and East Asia, which has fueled scientific interest in seismic design. This study focuses on the performance-based seismic design of spar floating wind turbines. Spar is a ballast stabilized structure anchored to seabed using catenary mooring lines. A three-dimensional model of the platform-mooring-anchor system is developed in ABAQUS CAE, where the soil is modeled using non-linear Winkler’s spring. The hydrostatic stiffness is represented using springs. Hybrid beam elements (high axial stiffness compared to bending stiffness) are used to model the mooring line. The effect of high-intensity earthquake shaking, peak ground acceleration, predominant frequency, and the impact of combined seismic-wave loading are evaluated in detail. Wave loads are observed to govern the design of spar wind turbines. In all the cases considered, seismic responses are found to be minimal. This preliminary study noted that spar floating wind turbines are less susceptible to earthquake dynamics due to the catenary shape, low mass of cable, and the long natural vibration period. This study will help to evaluate the feasibility of spar floating wind turbines in seismically vulnerable areas.