Fatigue damage model of wind turbine composite blades under uncertain wind speed

Abstract

This paper presents a load spectrum and estimates the fatigue life of composite blades of horizontal axis wind turbines. The distributions of aerodynamic loads are analysed by beam element momentum theory, which affects the fatigue life of the blade along with other loads such as gravity and wind shear. The wind speed follows Weibull distribution and wind speed over an hour time is generated based on the offshore wind parameters. Then, the maximum stress caused by the deterministic dynamic loads, such as aerodynamic load, gravitational pressure and wind shear effect, is calculated using finite element model by Ansys. The stress cycle is established by Fast Fourier transform of the load spectrum which converts the time domain to frequency domain. Fatigue damage performance and the fatigue life estimate for blades are used to be predicted by fatigue damage rule for each cycle during the service life of offshore wind turbine based on the Goodman diagram and S-N curve. Finally, safe working life is predicted by applying the Miner's law for linear fatigue damage accumulation. A numerical example of composite blades of a wind turbine is investigated by proposed method to estimate fatigue life under uncertain wind speed in the offshore environment. From the results, the proposed method can provide an effective tool for evaluating the fatigue damage and assessing structural performance of the wind turbine blades under the uncertain offshore wind.