Vibration Properties of Dual-Rotor Systems under Base Excitation, Mass Unbalance and Gravity

Rotor systems installed in a transportation system or under seismic excitations are considered to have a moving base. Although extensive research has been conducted on the dynamic behavior of the single-rotor system under base motions, few studies have dealt with the dynamics of dual-rotor systems, especially the counter-rotating dual-rotor systems used in airplane engines. Moreover, mass unbalance and gravity are unavoidable excitations for most rotor systems. Therefore, the vibration properties of a counter-rotating dual-rotor system with the coupled effects of base motions, mass unbalance and gravity are investigated in this paper for the first time. Using the Lagrange principle associated with the finite element method, a general model for dual-rotor systems under base motions was established by using Timoshenko beam elements, leading to a detailed analysis of the natural properties and harmonic responses of the system. The results revealed that different whirling modes (backward, forward or both) may be mutually excited. This research can be helpful for the design and vibration analysis of dual-rotor systems concerned with base motion.