Dynamic response analysis of the helicopter blades with non-uniform structural properties

摘要

In this study, a new general Finite Element Method (FEM) with variable order is utilized to solve the nonlinear first-order partial differential equations presented by Hodges [1] for analyzing initially curved and twisted anisotropic rotating beams subjected to arbitrary articulated boundary conditions. It is particularly attractive for the simulation of the non-linear structural dynamic response of hinged and hingeless helicopter blades with uneven structural properties distributions, especially those with sharp variations from section to section. A geometrically-exact and fully intrinsic theory is used here for dynamics of composite blades undergoing large deformation. The formulation is said implicit because the beam displacement and rotation variables are not included in the state vector form. Although the equations are geometrically exact, the highest degree of nonlinearity is quadratic and they do not have infinite-degree nonlinearities found in other methods. Application of method to specific examples is performed. The effect of presence of flexible joints between the hub and blade is investigated using two hinges in the flapwise and lead-lag directions, respectively. For verification purposes, the linearized beam Campbell diagrams are obtained and compared with those produced by the commercial program FLIGHTLAB for the same rotor blade. In addition, experimental tests are used to validate the proposed method. Nonlinear time domain dynamic responses are also obtained and validated against FLIGHTLAB. Based on the results and the performed comparisons for two different types of connections between the blade and hub, good accuracy of the FEM algorithm is demonstrated.