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.

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