Analytical study on longitudinal vibration characteristics of the coupled shaft and conical-cylindrical shell

Abstract

The inevitably produced vibrations during navigation will reduce the reliability of ships. The propulsion shaft system and the hull are connected by bearings to form complex longitudinal coupled vibrations. The study of longitudinal coupled vibration mechanism and its transmission characteristics during the navigation is of great significance for the reduction of vibration and noise. In this study, the longitudinal vibration model of the conical-cylindrical shell and homogeneous shaft is established by the analytical method, while the accuracy of the analytical solution is verified by finite element method (FEM). Both the propeller excitation on the shaft and the external excitation on the shell are under consideration, and in view of the uneven flow field around the hull, the excitation applied to the shell is set to be asymmetrical. Based on this model, the effects of coupling effect, fluid loading, excitations, bearing stiffness on the longitudinal vibration of the system are analyzed, respectively. The results show that the coupling effect between the longitudinal vibration of the shaft and shell is evident and is greatest under the excitation on the shell in a lower frequency range. Moreover, besides of damping and mass effects, the fluid loading on the hull also influence the vibration response of the shaft, due to the coupling effect. The increase of the bearing stiffness strengthens the coupling effect of shaft-shell. These findings are helpful for analyzing the vibration mechanism of the stern and provide control direction for ship structural vibration in the design stage.