Fatigue life assessment of offshore wind turbine support structures considering damage state adaptation and material stiffness effects

This study proposes a nonlinear fatigue damage accumulation model for fatigue life assessment of offshore wind turbine support structures considering material stiffness effects and a damage-state adaptive mechanism. An equivalent damage mapping index is first developed to represent the influence of material stiffness effects on nonlinear fatigue damage. A dynamic nonlinear transition index is then developed to represent the global spectrum envelope memory mechanism under multilevel variable-amplitude loading conditions. The nonlinear fatigue damage accumulation model is developed to assess the fatigue life of offshore wind turbine support structures. The feasibility and superiority of the proposed method is validated by the various metal materials from offshore wind turbine support structures. The results indicate that the proposed model provides superior predictive performance, with lower root mean square error and more concentrated error distributions than existing models.