Instability mechanism and criterion of wind-wave co-generation structural system under typhoon-wave-current coupled action

The deep and remote ocean environment is complex and variable, the wind-wave co-generation structural system is prone to violent oscillations or large displacements under the extreme coupled environment of typhoon-wave-current, and even to capsize instability, while the existing researches have neglected the instability process and the intrinsic mechanism of the wind-wave co-generation structural system under the extreme environment. In this study, a novel wind-wave co-generation structural system is proposed by integrating the semi-submersible wind turbine and the heave-type wave energy converter, the refined simulation of wind-wave-current coupled for Typhoon Rammasun is carried out by combining mesoscale WRF-SWAN-FVCOM (W-S-F) coupled simulation method, and a wind-wave-current multi-layer coupled velocity field model is established. Based on the meso/small-scale nested method, a small-scale CFD numerical tank test is conducted to comparatively analyse the nonlinear vibration response rules of the wind-wave co-generation structural system under different sea conditions. Furthermore, the critical instability wind speed of the wind-wave co-generation system is investigated by combining with the incremental dynamic analysis method, the instability mechanism of the wind-wave co-generation system under extreme marine environment is revealed, and the instability criterion is established. The study demonstrates that the wind-wave co-generation structural system will eventually capsize instability due to excessive pitch with the gradual increase of the wind-wave current environmental load, and the critical instability wind speed is 79 m/s. When the pitch angle of the wind-wave co-generation structural system is greater than 11.6°, the structure will undergo pitch instability. This study can provide engineering reference basis for the stability design and optimisation of this kind of offshore wind-wave co-generation structural system.