Modal Analysis Comparison of Beam and Shell Models for Composite Blades

The composite blades of wind turbines are made up of composite shell components. However, blades are often simplified as Eulerian beam in finite element analysis. In design both special and general purpose finite element codes are used worldwide. The verification of a special finite element code BModes vs. a popular general purpose finite element code ANSYS are performed via a uniform blade in both still and spinning cases in this paper. The test reveals that general finite element codes like ANSYS might overestimate the lag frequencies in spinning case. After verification of beam model, the approach is applied to complete the modal analysis of a practical wind turbine blade. The results are compared with a known shell model from literature. The comparison validates the simplified Eulerian beam model. Finally a guideline of usage for these two models is given.