Strength Analysis for a Jacket-type Substructure of an Offshore Wind Turbine Under Extreme Environment Conditions

This study investigates the extreme environment conditions behaviors of a reference offshore wind turbine with jacket substructure for transitional water depths. Fully coupled, nonlinear time-domain simulations on full system models are carried out under earthquake and typhoon loads. For a further insight into the importance of seismic and typhoon assessment, a comparison with demands from some typical design load cases prescribed by International Electromechanical Commission standard IEC 61400-3 is also provided. It is shown that earthquake loading may cause a significant increase of stress resultant demands, especially for seismically active areas. In addition, the results also showed the vertical accelerations at the ground surface were amplified by a factor of 8 at the location of the tower top. Larger structures with lower natural frequencies may be prone to significant responses of excitation in the vertical direction. This acceleration can have significant bearing on the design of the tower and its connection to the nacelle and performance of the turbine after the earthquake.