Reliability-based Gear Contact Fatigue Analysis for Wind Turbines under Stochastic Dynamic Conditions

Abstract

This paper describes a method to perform reliability-based gear contact fatigue analysis for wind turbines considering the long-term stochastic wind conditions. A simplified predictive subsurface pitting model for estimating gear fatigue lives is applied to establish the “so-called” limit state function. The National Renewable Energy Laboratory (NREL)’s 750kW land-based wind turbine is used to perform time domain simulations considering all wind speeds that the turbine will experience. The long-term distribution of the wind speed is described by a generalized gamma distribution. The time series of the torques in the main shaft are obtained from the global dynamic response analysis of the wind turbine. The time series of the gear contact forces are obtained from the dynamic analysis of the gearbox through multi-body simulations. The 2- parameter Weibull distribution is used to fit the long-term probabilistic distribution of the gear tooth contact pressures. Finally the fatigue reliability assessment is performed and the sensitivity of the reliability index on the selected random parameters is studied.