The effect of time-periodic base angular motions upon dynamic response of asymmetric rotor systems

Abstract

The effect of time-periodic base angular motions upon dynamic response of asymmetric rotor systems is investigated in this article. Both the disk and rotating shaft with asymmetric cross sections are considered. The rigid rotor base rotates around the three axis with time-varying angular speeds. Equations of motion for every components (asymmetric disk and shaft elements) are derived to assembe the finite element model of the whole rotor-bearing system. Due to the rotor asymmetries and angular motions of the rigid base, the finite element model has time-variable mass, gyroscopic, and stiffness coefficients. Parametric instability regions and rotor center orbits are compared with references’ results for model verifications. Then, forced responses of the system under unbalanced excitations, shaft asymmetry, and base angular motions are obtained. Effects of various types of angular motions, amplitudes, and frequency of base motions upon the response spectra and external resonances are discussed. As long as the periodic base angular motion is considered, both the response spectra and external resonances change significantly. Additional frequencies, including base frequency and combined frequencies, are found in the response spectra. Besides the critical and half-critical resonances (for the asymmetric rotor system), there are multiple resonances after considering the periodic base motions.