Combination resonances of a dual-rotor-bearing-casing system

In this paper, the combination resonance characteristics of a high-dimensional dual-rotor-bearing-casing system with bearing nonlinearities are presented. All the periodic solution branches, including the unstable solutions of the system, are obtained by the semi-analytical harmonic balance method. Two primary and two combination resonance regions are found in the amplitude–frequency responses, with the vibration jump and multiple solutions phenomena being observed. Furthermore, the amplitude–frequency responses with separated frequencies are analyzed; it is shown that the vibration responses of the combination resonance regions are dominated by the combination frequencies of the rotating speeds of the high- and low-pressure rotors. Moreover, parametric analysis shows that the combination resonances are sensitive to the change in the inter-shaft bearing clearance. With the increase in clearance, the combination resonance regions are widened. The results in this paper provide a better understanding of the combination resonances in high-dimensional dual-rotor-bearing-casing systems.