Fatigue life analysis of offshore wind turbine under the combined wind and wave loadings considering full-directional wind inflow

Abstract

Fatigue damages of an offshore wind turbine (OWT) would be caused by long-term wind and wave loads, necessitating the importance of fatigue life analysis to ensure the in-service behaviors of OWT. This study evaluates the fatigue damage and predicts the fatigue life of OWT considering full-directional wind inflow under the coupling effects of non-Gaussian wind field and wave. The forces and bending moments are assessed in three types of the wind field, i.e., Gaussian, softening non-Gaussian, and hardening non-Gaussian, according to the Kaimal spectrum by using OpenFAST. The dynamic responses of OWT are implemented by a three-dimensional finite element model (FEM) established by ABAQUS. The fatigue life is assessed in the tower base section and the pile of OWT under different loading combinations. Results show that the crack initiation life is greatly affected by the non-Gaussian wind field, while the crack propagation life is not that sensitive. The fatigue life of OWT under a full-directional wind inflow is approximately three times longer than that under a single-directional wind inflow. It is recommended to consider full-directional wind inflow in the non-Gaussian wind field for OWT design.