Multi-hazard performance assessment of monopile offshore wind turbine considering coupled corrosion and fatigue damage

Monopile offshore wind turbine (OWT) often suffer from chloride corrosion and wind–wave fatigue during service. However, studies focus on the impact of pitting or uniform corrosion on fatigue damage, with less attention to their interaction as well as the coexistence of pitting and uniform corrosion, which produces errors in the estimation of the local defects caused by coupling damage and the residual performance of the structure. Most OWT monopiles are constructed with flexible thin-walled structural systems, which are sensitive to local defects and prone to local buckling failure. Thus, insufficient consideration of the corrosion fatigue effect clearly reduces the reliability of OWT failure mode identification and multi-hazard vulnerability analysis. To solve this problem, Faraday's law and continuous damage mechanics were used to establish models for pitting and uniform corrosion damage. A cross-sectional segmentation strategy was employed to consider nonuniform fatigue damage caused by directional fatigue loads. Then, the corrosion and fatigue coupling damage of OWT was evaluated. The results show that considering coupling damage causes the failure mode of the OWT to change from overall bending to local buckling. Quantifying OWT vulnerability under earthquake-hurricane action shows a 9.57% collapse probability with coupling damage, compared to 3.18% without it.