Aero-Hydrodynamic Coupled Dynamic Characteristics of Semi-Submersible Floating Offshore Wind Turbines Under Inflow Turbulence

In this study, the frequency characteristics of the turbulent wind and the effects of wind-wave coupling on the low- and high-frequency responses of semi-submersible floating offshore wind turbines (FOWT) are investigated. Various wave load components, such as first-order wave loads, combined first- and second-order difference-frequency wave loads, combined first- and second-order sum-frequency wave loads, and first- and complete second-order wave loads are taken into consideration, while different turbulent environments are considered in aerodynamic loads. The comparison is based on time histories and frequency spectra of platform motions and structural load responses and statistical values. The findings indicate that the second-order difference-frequency wave loads will significantly increase the natural frequency of low-frequency motion in the responses of the platform motion and structure load of the semi-submersible platform, which will cause structural fatigue damage. Under the action of turbulent wind, the influences of second-order wave loads on the platform motion and structural load response cannot be ignored, especially under extreme sea conditions. Therefore, in order to evaluate the dynamic responses of semi-submersible FOWT more accurately, the actual environment should be simulated more realistically.