Fatigue life analysis of offshore wind turbine tower under combined action of wind and wave

In order to obtain the fatigue life of an 8 MW offshore wind turbine tower, the fatigue damage characteristics of tower under combined action of wind and wave were analyzed. The calculation method of fatigue damage degree of the tower under different working conditions in unit cycle time is given. Based on the linear extension theory of fatigue damage, the annual fatigue damage degree of the tower under different working conditions was calculated, and the fatigue life of the tower was obtained. The calculation results show that the fatigue life of the tower is 31.2 years when the ideal S-N curve is adopted, which is longer than the design life of 25 years. The influences of average stress, roughness and structure size on S-N curve are analyzed. When Goodman method is selected for average stress correction, roughness coefficient is 0.473, and dimension correction coefficient is 0.639, the fatigue life of the tower is 26.7 years, decreasing by 14%. The fatigue life of the tower under different roughness is calculated. The calculated results show that the fatigue life of the tower decreases with the decrease of the roughness coefficient. When the roughness coefficient is 0.287, the fatigue life of the tower is about 25 years.