Analyses of offshore wind turbine structures with soil-structure interaction under earthquakes

This research provides an analysis framework for offshore wind turbine (OWT) support structures subjected to seismic, wind, and wave loads using the finite element method with soil-structure interaction, and a conservative soil liquefaction analysis is developed. The NREL 5-MW jacket-type OWT under IEC 61400-3 is analyzed. The results indicate that seismic loads combined with wind and wave loads during power production often control the design, especially near the rated wind speed. For earthquakes with a peak ground acceleration (PGA) smaller than 0.32 g and the dominant period (T_s) smaller than 1 s, the increase in steel weight due to seismic loads is small, because the amplification of the seismic loads is not obvious. For PGA over 0.52 g, almost all the members are controlled by the seismic loads, and the increase in the steel design weight can be over 40%. This paper also indicates that first-mode tuned mass dampers for jacket-type support structure with deep piles are efficient to reduce the vibration coupled from wind, wave, and seismic loads even with 20-m soil liquefaction.