Nonlinear dynamic analysis of a dual-rotor system with deteriorating rub-impact fault caused by loose disc

Rub-impact is one of the common failures in dual-rotor systems, and seriously affects the machine’s operation cost. Currently, research about this fault mainly focuses on models that gain initial excitation through rotor unbalance. Whereas, this excitation source is rarely aggravated during rotating machinery’s full life period. Aiming at this issue, a Hertz impact-contact model of casing-disc-shaft dual-rotor system with rubbing fault caused by disc looseness is developed to simulate a deteriorating failure. Thus, the system vibration variation during the fault deterioration can be analyzed, and the necessary basis for prediction of the coupling faults are provided. In this model, slight unbalance provides the initial excitation amplified by disc looseness, from which the rub-impact defect is induced between the loose disc and the outer casing. Further, motion equations for this coupling fault system are derived to simulate the vibration signals. Result shows that the critical parameters significantly affect the system’s vibration, and the deterioration of coupling faults takes the system from steady-state to chaotic-state. The study of this paper provides theoretical bases for the rub-impact fault tracing of dual-rotor systems, and proposes different scales to indicate the fault severity degree qualitatively and quantitatively.