Vibration analysis of a coupled propulsion shaft-shell system based on the numerical and semi-analytical methods

The bidirectional coupling characteristics of vibrations for the propulsion shaft and the combined shell should be produced in the ocean conditions. Many previous studies always simplified the coupling relationship between the propulsion shaft and the combined shell, which neglected the deformation of the flexible shell or the time-varying stiffness of the support bearings. In this work, a comprehensive dynamic model of the flexible propulsion shaft-combined shell system is established, which considers the time-varying stiffness and contact forces of the bearings. A solution strategy approach combining the numerical and semi-analytical methods is adopted to improve the computational efficiency and reasonable accuracy of the previous methods. The dynamic responses of the system with the time-varying and time-in various bearing stiffness are compared to show the advantages of the proposed model. Note that the time-varying stiffness of the bearings can significantly affect the vibrations of the flexible coupled system. Moreover, the influences of the flexible shell thickness, eccentricity errors of the flexible shaft, and the bearing arrangements on the coupled system's vibrations are investigated. The findings can provide some references for the optimization methods of the vibration and noise reduction in underwater vehicles.