Coupled bending-torsional vibration analysis of rotor with rub and crack

Rotor–stator rub and fatigue crack of the shafts are two important rotor faults. They have detrimental effects on health and reliability of the rotating machinery. In this paper, modelling and vibration signature analysis of rotor with rotor–stator rub, transverse fatigue crack and unbalance is attempted. The rotor–stator interaction effects on the response of a rotor are investigated in the presence/absence of a transverse crack. The torsional vibrations are investigated for their sensitivity to rubbing using finite element model that also accounts for cross coupling of stiffness introduced due to crack. Due to the presence of both rotor–stator rub and transverse crack in a horizontal rotor, the system becomes highly nonlinear. The time localised rub excitations and nonlinear stiffness variation due to breathing of the crack influence the rotor response in both lateral and torsional modes and are explored extensively using Hilbert–Huang transform with the objective of unravelling some unique features of these faults that may be useful for fault identification.