Structural Dynamic Modeling for Rotating Blades Using Three-Dimensional Finite Elements

This paper deals with the development of an analysis model capable of analyzing the structural dynamic behavior of rotating composite blades. An eighteen node solid-shell finite elements were successfully used for the analysis of blade structures undergoing large deformation. The analysis model includes the effects of transverse shear deformation, Coriolis effect and elastic couplings due to the anisotropic material behavior. Incremental total-Lagrangian approach was adopted to allow estimation on arbitrarily large rotations and displacements. The equations of motion for the finite element model were derived by using Hamilton's principle, and the resulting nonlinear equilibrium equations were solved by applying Newton-Raphson method combined with load control. The present numerical results were compared to several benchmark problems, and the results showed a good correlation with the experimental data and other finite element analysis results. The vibration characteristics of shell and beam type blades were investigated. For shell type blades, blade curvature and geometric nonlinearity significantly influenced the dynamic characteristics, and only the geometric nonlinear analysis model can captured the frequency loci veering phenomena. For beam type blades, one-dimensional beam and three-dimensional solid models gave comparable prediction for the straight and large aspect ratio blade. As the blade aspect ratio decreased, considerable differences appeared in bending and torsional natural frequencies.