Detailed Nonlinear Model for the Analysis of a Wind Turbine Pitch Bearing

Presentation by Aitor Fernandez, Mechanical Engineer at IK4-Tekniker.

The mechanical behavior and failure mechanisms of a wind turbine pitch bearing are very different from those of other bearings types designed for traditional applications. On the one hand, there is the effect of the low relative stiffness of the surrounding elements such as the hub or the blades. On the other hand, the oscillating and low amplitude nature of its rotary motion favors certain specific failure mechanisms. Therefore, the approach taken by existing international standards does not match their actual behavior and that is why alternative approaches are needed.

This paper presents a methodology based on a finite element model generated by HyperMesh. Given the size and complexity of the model, the rolling elements have been simplified by their equivalent stiffness. This non-linear stiffness and its large displacements are considered in a non-linear calculation solved by OptiStruct. Its reasonable computational cost allows the analysis of the large number of extreme and fatigue loadcases. By means of sub-modelling techniques, other local phenomena such as the tensional state of the rings have been analysed. The information obtained through HyperView enables the verification of the behavior under extreme loads, life, fretting or core crushing.