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Composite pretwisted rotating thin walled beams (TWB) can be used as the structural model for composite helicopter and wind turbine blades for the study of aeroelastic response of the blades. In the present study, semi-analytical solution is performed for the free vibration analysis of uniform and asymmetric composite pretwisted rotating TWB. The approximation of the Green-Lagrange strain tensor is adopted to derive the strain field of the system. The Euler–Lagrange governing equations of the dynamic system and the related boundary conditions are derived via Hamilton’s principle. In order to solve the governing set of equations, the Extended Galerkin’s Method (EGM) is employed. For this purpose, the structural variables are separated in space and time and the assumed mode shapes are defined to satisfy the essential boundary conditions. For the purpose of validating the TWB model developed, the commercial finite element analysis tool, MSC Nastran is used to compare the results of modal analysis obtained by the present structural model with the finite element solution. With the results obtained in this paper, it is aimed to ascertain the effect of various coupling in circumferentially asymmetric stiffness (CAS) and circumferentially uniform stiffness CUS configurations, pretwist, angular velocity and fibre orientation, on the natural frequencies and the mode shapes of the rotating thin-walled composite beams. The results are expected to propose better predictions of the vibrational behavior of thin walled structures in general, and in the design of rotor blades of turbomachinery, rotorcraft and wind turbine systems, in particular.

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Different detailed finite element model alternatives are developed to come up with the most reliable finite element model of the sandwich panel, with the actual honeycomb core geometry, to evaluate the existing equivalent continuum models of aluminum honeycomb cores. Finite element models of sandwich panels with effective elastic constants of the honeycomb core are generated based on the existing continuum models of the honeycomb core. The evaluation of the effective elastic constants of honeycomb cores is based on the comparison of the total reaction forces, calculated by both finite element models, on the supported faces of sandwich panels due to different in-plane and out-of-plane uniform input displacements applied to the faces of the panels. The results show that the reliability of the individual in-plane and out-of-plane effective elastic constants of the existing continuum models of the honeycomb cores can be successfully evaluated based on the comparative study.