Assessment of Wind-Induced Responses and Fatigue Performance of Spar-Type Floating Offshore Wind Turbines Considering Uncertainty in Field-Measured Wind Speed Profiles

Abstract

The mean wind-speed profile is an important input for wind-load evaluation. In most previous studies, wind-profile parameters are assigned deterministic values for evaluating wind-induced responses. However, recent field measurements reveal substantial variability in wind profiles, particularly under typhoon climates. Therefore, in this study, based on wind observations along the southeastern coast of China, the wind-profile parameter is treated as a random variable to assess structural responses and fatigue performance under normal wind and typhoon climates. First, optimal near-surface wind-profile model for the two climates is identified from wind observation data, and the probability distributions of the uncertain parameters are established. Then, a framework based on dimension-reduction spectral representation and representative-point selection scheme is proposed for evaluating floating offshore wind turbine (FOWT) responses and fatigue damage equivalent loads (DELs) under wind-profile uncertainty. Finally, quantitative analysis of the influence of wind-profile uncertainty on National Renewable Energy Laboratory (NREL)’s OC3-Hywind spar FOWT is conducted as a case study using a 15-degree-of-freedom (15-DOF) aero–hydro–servo–elastic model formulated within an analytical-dynamics framework based on the Euler–Lagrange method. Results show that the mean and standard deviation of structural responses are negligibly affected by wind-profile uncertainty under normal-wind conditions. Under typhoon conditions, when wind-profile uncertainty is considered, the standard deviation of blade flapwise displacement increases by 57.03%, while the standard deviations of blade-root DELs increase by 202.00% (flapwise) and 143.99% (edgewise) considering wind-profile uncertainty.