Determination of vibration characteristics of multiple-load-path blades by a modified Galerkin's method

A modified Galerkin's method is developed to determine the natural vibration characteristics of multiple-load-path rotor blades. The development follows parallel to the CAMRAD program procedure for a single load-path-blade. Two types of finite series expansion functions are utilized: exact transcendental solutions to nonrotating uniform beam problems, and polynomial functions. A computer program based on this method is developed to determine the free vibration characteristics of multiple-load-path blades undergoing coupled flapwise bending, chordwise bending, twisting and extensional motions. Numerical results are obtained for two rotors. The first has constant properties along the span and the second is modelled from a nonuniform experimental rotor with discontinuous properties. Natural frequencies compare well with those predicted using a finite element approach, and with the experimental results for the second rotor.