Longitudinal vibration of marine propeller-shafting system induced by inflow turbulence

The multi-modal vibration characteristics of a ten-bladed marine propeller and its shafting system induced by the inflow turbulence are numerically investigated. Firstly, the distributed pressure on the propeller face is computed by the correlation method according to the statistical characteristics of isotropic turbulence. Next, the mapped unsteady pressure is applied on the blades and the associated random vibration responses of the immersed elastic propeller and its shafting system are computed by using the modal superposition method. Finally, vibration characteristics of the propeller and its unsteady thrust transmitted to the foundation are analyzed with different dynamic parameters of the system. The results show that amplification of the unsteady thrust associated with the low-order bending modes of the propeller blades cannot be neglected, especially when the frequency of the first bending mode approaches that of the longitudinal vibration mode of the shafting system. The propeller with 'soft' blades suffers higher excitation intensity at its first natural frequency but the corresponding modal hydrodynamic damping may be enhanced.