Comparing a fracture mechanics model to the SN-curve approach for jacket-supported offshore wind turbines: Challenges and opportunities for lifetime prediction

Accurate lifetime predictions are needed for support structures of offshore wind turbines to optimize operation and maintenance and to decide about lifetime extension of aging wind farms. A comparison of a facture mechanics model to the SN-curve approach for jacket supported offshore wind turbines shows that it is attractive for lifetime extension decisions; however major challenges are calibration of material parameters and assumptions for initial crack size. Crack growths on a Y-joint connecting brace and jacket leg was analysed with simulations of structural response to aero- and hydrodynamic loading and Paris' law for crack propagation. The model was calibrated to yield an identical fatigue life as obtained from the SN-curve analysis. The effect of weather seasonality on crack growth was evaluated with a Markov weather model and Monte Carlo simulations. Results show that crack growth is sensitive to parameter calibration and follows seasonal weather trends.