Bifurcation shifts in a rotor-stator contact system under frictional forces to higher rotational speeds caused by stator thickness

Accurate simulations of detrimental vibrations observed in a rotor-stator contact system are beneficial. Existing contact models that consider the contact configurations between the rotor and stator cannot deal with the frictional forces simultaneously, thereby not realizing analytical accuracy. This study proposes a contact model that concurrently incorporates these factors for achieving a high-precision expression of detrimental behaviors. The model identifies rotor-stator contact by evaluating their geometric shapes and orientations. In addition, it formulates the influences of contact corresponding to the contact configurations and frictional forces by using external forces and moments derived from the Kelvin–Voigt and smoothed Coulomb models. This study analytically investigates the effects of contact configurations, especially stator thickness, on the nonlinear dynamics of a rotor-stator contact system under frictional forces. The analysis focuses on an overhung rotor modeled via the finite element method. Bifurcation analysis reveals that the bands where key behaviors observed in a rotor-stator contact system under frictional forces such as asynchronous partial contact and backward whirling motions occur expand and shift toward higher rotational speeds as stator thickness increases. This shift is caused by the enhanced stiffening effect resulting from the substantial reduction in clearance and external moments induced by normal forces acting on the side of the stator due to consideration of the stator thickness. Additionally, the stiffening effect is further enhanced by increased penetration, which results from the elevated input energy due to increased frictional forces arising from the substantial reduction in clearance and suppression of rotor deformation because of the external moments induced by frictional forces. The proposed contact model and its findings contribute to improved safety and optimized design in rotating machinery systems.