Uncertainties in damage prediction of wind turbine blade under random gust

Preprint, 2013

In the design of wind turbine structures, aeroelastic stability is of utmost importance. The bending-torsion oscillation problem of a representative rotor blade section with structural nonlinearity has been considered. The system is subjected to horizontal random gust modeled as a stationary process. Uncertainty quantifiation in high- lighting the relative importance of different sources of uncertainty on aeroelastic system stability, consequently its fatigue and failure is a crucial step of aeroelastic design. Effect of different sources of un- certainty on the fatigue damage estimate of the blade are studied in the present aeroelastic problem. The effect of the following on the fatigue damage estimate of the blade is reported in this work, struc- tural parameter, choice of aeroelastic model (modeling error) and also the stress selection criteria for the damage estimate. The structural parameter randomness is modeled through polynomial chaos expan- sion in analyzing its effect on the damage estimate. The unsteady inviscid ow-field in the aeroelastic model is resolved analytically and also using a higher fidelity vortex lattice algorithm and the relative effect on damage is seen. Finally, the effect of fatigue damage criteria selection is also observed. The damage calculation is done for torsion only, bending only and also for multiaxial stress situations. Multiax- ial stresses are converted to an `equivalent' one by using a signed von Mises criterion. A linear damage accumulation rule has been used to estimate the risk for fatigue damage.