Experimental verification of the mechanism on stick-slip nonlinear friction induced vibration and its evaluation method in water-lubricated stern tube bearing

Water lubricated stern tube bearings are widely used to support the propeller shaft in marine applications. The material of the stern tube bearing is usually rubber or polymer. Since water creates the lubricating film at the shaft-bearing interface, the friction coefficient on the bearing in the boundary and mixed lubricating area where the friction induced vibration frequently occurs is usually higher than that of oil. Furthermore, the friction coefficient is reduced as the speed of the shaft revolution increases within the regime in which static friction is dominant. In this case, the shaft-bearing system can become unstable due to the stick-slip motion of the shaft bearing system, and self-excited vibration can occur. In this study, the shaft-bearing system is described using a two degrees of freedom model, and a stability analysis is performed in accordance with system parameters such as normal load, damping on the bearing, and the natural frequency of the shaft system related to the stick-slip motion at the shaft-bearing interface. In addition, stick-slip nonlinear friction induced vibration is reproduced with a test unit that can simulate stick-slip nonlinear friction induced vibration of the propulsion shaft of the ship. We attempt to how the stick-slip vibration is identified using signal processing of the test unit acceleration.