Uncertainties in loading and material parameters

Remaining useful life (RUL) prediction of wind turbine gearboxes is especially important since the failure of the gearbox is not only costly but also causes the longest downtime. One of the most common causes of the premature fault of wind turbine gearboxes is attributed to the fatigue fracture of gear tooth due to fluctuating and cyclic torque transmitted to the gearbox caused by fluctuating wind loading. Moreover, the fluctuation of the torque as well as the inherent uncertainties of the material properties results in uncertain RUL prediction. It is therefore essential to quantify these uncertainties in RUL estimation of gears. A six degree of freedom dynamic model of a single stage gearbox was developed. Torque spectrum data of a wind turbine rotor was scaled and used to simulate the stochastic characteristic of the loading. Uncertainties in Paris’ and material constants were also quantified. A framework was developed for the estimation RUL of gears with uncertainties in loading and material parameters. The dynamic analysis shows an increased dynamic loading with increasing crack length. It was demonstrated that uncertainty quantification of load and Paris’ material constants is crucial in RUL prediction. The results of the dynamic analysis depicted an increase in dynamic force with increasing crack size. The increase in the crack size also caused an increase in the stress intensity factor. Finally, it was shown that probabilistic analysis provides the probability of failure of gears at any time step. This information is useful in scheduling maintenance and replacement.