Comparative Assessment of Finite Element Modeling Techniques for Wind Turbine Rotor Blades

摘要

Structural analysis of wind turbine blades has historically utilized cross-sectional analysis methods or 2D layered-shell finite element models in conjunction with relatively large safety factors to predict the structural behavior of rotor blades. More recently the use of high-fidelity modeling methods including nonlinear analysis, solid elements, and higher order elements have been suggested in the literature, resulting in a wide range of recommended modeling practices without a clear consensus on the appropriate modeling fidelity necessary to analyze a blade. In this work, a representative wind turbine embedded spar cap feature is selected for a comparative study to assess the relative accuracy of 18 modeling approaches. The selected methods consider layered-shell and layered-solid elements, various element formulations and plate theories, smeared and discrete ply representations, and through thickness discretization of solid models. In addition to comparing the 18 modeling methods for the base configuration, a model-generation tool was written to allow for the rapid generation of finite element models for variations in the base geometry and laminate. Using this tool, a trade study is performed to vary the spar cap and core thickness relative to a fixed skin thickness. In doing so, this comparative study provides the necessary information to identify the relative error in component stresses and strains used as inputs to assess failure. Outcomes of these trade studies show artificial extension of the webs for element connectivity result in shell models that are overly stiff, underpredicting peak fiber strain by 10% or more. However, as the overall section height increases, this modeling accuracy improves. All solid modeling methods considered are seen to predict peak fiber strain within 1-2%. Refined through thickness discretizations are seen to be necessary to represent nonlinearities observed in the transverse response, and therefore many of the lower fidelity methods considered here have high errors, in excess of 20% for in-plane transverse and shear stresses. High interlaminar shear stress gradients are seen to exist due to the shear load transmitted between the shells and webs, and even the highest fidelity methods show limitations which require further investigation.