Wind-Induced Failure of Wind Turbines

Models of loading and structural behaviour for use in lifetime prediction of propeller type wind turbines are discussed. The emphasis is on wind-induced loads, which are separated into periodic dynamic loads due to rotation in the spatially nonuniform mean windfield, and stationary stochastic loads due to wind turbulence.

Turbulence is represented by auto- and cross-spectra of the turbulent wind speed fluctuations. The spectra are derived, however, for the turbulence as seen from points of a rotating wind turbine blade, which significantly changes the shape of the spectra. Structural response is calculated in the frequency domain and the stress responses appear as a combined periodic and stochastic signal.

A fatigue model and a simple approach to extreme response calculations have been derived, which take into account both the periodic and the stochastic parts of the stress response. Assuming that failure occurs either by a slow accumulation of damage or by a sudden exceedence of a critical value for the stresses, the models can be used in the design phase when predicting the lifetime and assessing the safety of a wind-turbine structure.

Finally, results from applying the model are presented and compared with available measured data.