Coupled dynamic analysis of a heavily-loaded propulsion shafting system with continuous bearing-shaft friction

Abstract

This paper studies the friction-induced instability and nonlinear dynamics of a heavily-loaded slow speed propulsion shafting subjected to the uninterrupted contact between the shaft and the water-lubricated rubber bearing. A high-dimensional analytical model is developed to take into consideration the intrinsic interactions among the torsional and lateral vibrations of the continuous shaft, bearing vibrations and the friction nonlinearity. The exponential friction model derived from experimental data is adopted to qualitatively represent the velocity-dependent behaviours of friction for water-lubricated rubber bearings. A stability analysis based on the complex eigenvalue calculations of the linearised system is performed to estimate the effects of parameter variations on instabilities. Two potential instabilities concerning the self-excited whirl motions and stick-slip torsional motions are identified. Corresponding transient dynamics are then numerically studied to explore the roles of different types of vibrations on nonlinear behaviours. The results reveal that the velocity-weakening and discontinuity effects of nonlinear friction may induce the occurrence of limit-cycle type self-excited vibrations for both instabilities. Additionally, the effects of cross-coupling and the kinematic coupling at the bearing-shaft interface on the dynamic interaction among different vibration modes are also highlighted.