A spectral fatigue assessment framework for floating offshore wind turbines

Cyclic loads caused by wind and waves pose great challenges to floating offshore wind turbine (FOWT) structures and influence their fatigue safety; consequently, cyclic loads should be considered early in their design stage. In this study, by comparing various spectral models and their correction methods to perform fatigue assessment using the OpenFAST for simulating the coupled dynamic response of FOWT, a so-called White Noise approach is proposed to estimate the short-term fatigue of FOWT under all possible sea states based on a limited number of simulations. Comparing the results of the proposed method against other available spectral fatigue methods shows that it is necessary to use a non-Gaussian correction and wind band calibration factors for conventional narrowband spectral fatigue assumptions. In particular, second-order wave effects play an extremely important role in both FOWT fatigue damage models and applied spectral fatigue methods.