Effect of contact surface roughness on friction self-excited vibration of the propulsion shaft-bearing system

An appropriate assessment of the self-excited vibration of the shaft-bearing system is crucial for effectively enhancing the reliability of ships during operation. The characteristics of self-excited vibration are not only influenced by inadequate lubrication, but also by the roughness of the contact surface between the bearing and shaft. Therefore, a lubrication model that takes into account surface roughness, velocity-dependent friction model derived from experimental data, and a dynamic model for the shaft-bearing system is established. This paper discusses the effects of rotational speed and pressure on self-excited vibration by combining transient amplitude, harmonic frequency, and phase diagrams, and conducts experimental validation. It analyzes the relationship between surface roughness and the lubrication characteristics of the bearing. The dynamic equations of the shaft-bearing are combined to discuss the influence of surface roughness on self-excited vibration. This research indicates that changes in rotational speed and positive pressure can lead to frictional instability, resulting in self-excited vibration and “stick-slip” in the shaft-bearing system. Furthermore, the roughness of the contact area significantly influences system vibration, resulting in a decrease in the vibration amplitude of both the shaft and bearing. Notably, while the reduction in vibration amplitude for the shaft is subtle, that of the bearing exhibits a more pronounced decrease of approximately 40%. A smaller vibration amplitude for the bearing is observed as its roughness falls within the range of Ra2.4 to Ra3.2.