Refined Structural Dynamics Model for Composite Rotor Blades

Abstract

In this paper, a refined one-dimensional beam formulation based on a mixed variational approach has been developed for static and free vibration analyses of both rotating and non-rotating composite blades with elastic coupling. The present approach allows the modeling of either open-section or closed-section blades of arbitrary section shape, stacking sequence, and end restraint effects. The theory accounts for the effects of elastic coupling, shell-wall thickness, warping, warping restraint, and transverse shear deformations. A semi-complimentary energy function is used to derive, in a variationally consistent manner, the beam force-displacement relations. The free vibration analysis is validated against experimental test data and other analytical results for composite beams of various cross-sections such as box-section, rectangular solid section, and I-section. Good correlation is achieved for all the test examples. The influence of modeling refinements on the free vibration characteristics of composite blades through the current mixed formulation is also investigated. The wall thickness effects are shown to become significant when the thickness-to-depth ratio of the beam approaches approximately 30%. The effects are seen to be more at higher modes.