Collapse mechanism and failure criteria of offshore monopile wind turbine towers under coupled typhoon and strong earthquake effects in the eyewall region

The occurrence of a strong earthquake in typhoon eyewall, where wind speed and turbulence intensity reach their peak, may lead to a typhoon–earthquake coupled hazard. This poses a serious threat to the structural safety of offshore monopile wind turbines, potentially resulting in tower collapse and structural failure. To address these issues, the nonlinear dynamic response and failure mechanism of IEA 15 MW offshore monopile wind turbines under coupled typhoon–earthquake conditions is investigated. A mesoscale real-time coupling simulation method, WRF–SWAN–FVCOM (W–S–F), is established via the Model Coupling Toolkit (MCT), and a nested reduced-order simulation method bridging meso/microscale models is proposed. Incremental dynamic analysis (IDA) is then employed to quantify the effects of coupled loading on tower displacement and internal force responses. Finally, the progressive collapse behavior of the structure under strong earthquake is simulated, with an energy-based failure criterion proposed. Results show that the proposed meso/microscale W–S–F/CFD reduced-order method can effectively predict wind loads on wind turbines under typhoon conditions. When subjected to coupled typhoon and strong earthquake actions, the local plastic strain near the tower top reaches 0.15, suggesting that the tower cannot support the nacelle mass, leading to instability and collapse. The change in internal energy density before and after tower segment failure reveals a concave failure mechanism. When the energy-based failure index exceeds 1.5, the offshore monopile wind turbine fails structurally.