Study of lateral–axial coupling vibration of propeller-shaft system excited by nonlinear friction

Abnormal vibrations induced by the water-lubricated bearing-shaft friction will influence the normal operation of the propeller-shaft system. In order to study the influence of the friction effect on the axially loaded shaft system, a mathematical model of the coupled lateral and axial vibrations is developed based on a simplified propulsion-shafting system. The friction force is considered as a concentrated force and moment acting at the center of the journal which is nonlinearly elastic supported by the rubber bearing. The dynamic characteristic of friction coefficient, which is described by a Stribeck curve, varies regarding the relative velocity on contact surface. The unbalance and gyroscopic effect are also considered in this model. The rotating frequency is used as the control parameter to obtain the quantitative result in the numeric simulation. The results show that lateral self-excited vibration may occur and give rise to axial self-excited vibration. The effects of damping coefficients and attenuation factor of the Stribeck curve are studied. As a result, change of damping coefficient, attenuation factor and static clearance can lead to the effective control of abnormal vibrations and subsequent design improvement of the shaft system.