Instability mechanism and criteria of wind–wave co-generation structural system considering mooring failure under extreme sea conditions

<p indent="0mm">The wind–wave co-generation structure is a complex multiflexible–rigid dynamic system consisting of blades, nacelle, tower, pontoon, float, and mooring. Among these, the mooring is the core component and ultimate safeguard for maintaining the structural stability of the system under extreme sea conditions. To explore the instability mechanisms and criteria of the wind–wave co-generation structure in the event of mooring cable failures, this study introduces a novel structural system integrating a semisubmersible wind turbine with a pendant float. A mesoscale real-time coupling simulation method combining WRF, SWAN, and FVCOM (W-S-F) is developed and implemented using the model coupling toolkit platform. The spatiotemporal evolution of the typhoon–wave–current interaction during the entire transit of Typhoon <italic>Meranti</italic> is analyzed. The nonlinear vibration response behavior of the wind–wave co-generation structural system is investigated using the mesoscale nested downscaling simulation method (WRF-CFD/CSD). Furthermore, the jumping instability mechanism of the structural system is revealed based on the complete process of cable breakage, and instability criteria are established. The results show that the mesoscale W-S-F coupled simulation reduces the typhoon path prediction error by 33.4% and improves wind speed accuracy by 12% compared with the standalone WRF model. The motion of the wind–wave co-generation structural system during the mooring breakage process conforms to the jump instability mechanism. The displacements following the rupture of the main mooring and side mooring are mainly governed by longitudinal and transverse oscillations, respectively. At a displacement destabilization index <italic>w</italic> of ≥3%, the structural system transitions from the presteady stage to the jump instability stage owing to mooring failure and ultimately reaches the poststeady stage. The findings of this study offer a theoretical foundation for the stability design of wind–wave co-generation structural systems.