Analysis of the longitudinal coupled dynamic characteristics of shaft-shell system considering the lubrication of thrust bearing

Abstract

The propeller generates longitudinal pulsating forces in a non-uniform flow, transmitting through shaft-shell system and causing underwater acoustic radiation. The thrust bearing, as a key coupling component, exhibits variable stiffness and damping, affecting vibro-acoustic response of system. A numerical model based on fluid lubrication theory is developed to determine dynamic characteristics of thrust bearing oil film stiffness and damping. Analytical models for shell and shaft are created using Flügge's theory and Euler beam theory. The combined stiffness from oil film and bearing seat acts as a coupling parameter between shaft and shell, forming a semi-analytical dynamic model. This study examines the impact of thrust bearing dynamic characteristics on shaft-shell system's vibro-acoustic properties. Results show that at high rotational speeds, the increase in vibration and acoustic radiation is primarily due to growing excitation forces. Under constant excitation forces, higher rotational speeds enhance the lubrication performance of the thrust bearing, reducing vibrational energy transmission between shaft and shell. Increasing radius and circumferential width of bearing pads can enhance the lubrication performance of the thrust bearing and reduce vibro-acoustic radiation. Sensitivity analysis reveals that compared to circumferential width, the radius of bearing pads plays a more dominant role in determining both lubrication and vibro-acoustic performance. Increasing number of bearing pads may negatively impact lubrication of the thrust bearing, while it is beneficial for reducing vibration and noise.