Fatigue Assessment for Gearbox of a Floating Offshore Wind Turbine (FOWT)

Due to severe working conditions, the gearbox of a floating offshore wind turbine (FOWT) is prone to fatigue damage. Fatigue failure of the gearbox may lead to significant economic losses and even potential safety incidents. Therefore, fatigue assessment for the gearbox of a NERL Spar type 5MW FOWT is performed in this paper. The time histories of loading on the main shaft in different sea states are obtained through a series of timedomain analysis where the wind, wave, and current are accounted for. The gearbox which consists of a main shaft and a planetary gear set is modeled by finite element method (FEM) and the corresponding stress responses are computed by the dynamic analysis. Rain-flow counting is employed for the statistical analysis of the stress ranges on the gearbox. The fatigue life of each gear in the planetary gear set, as well as the main shaft, is predicted in terms of S-N curves and Palmgren-Miner’s rule. Fatigue strength of the sun gears, planet gears, and main shaft is investigated and the critical locations of gearbox where fatigue failure is prone to occur is discussed. The results are expected to provide a reasonable reference for structural safety assessment for the gearbox of FOWTs.