The bending vibration characteristic of a propulsion shafting and hull structure coupled system at low frequencies

In this paper, a finite element simulation model of the propulsion shafting and hull structure system is developed for analyzing the coupled bending vibration characteristic at low frequencies. The natural frequencies and modal shapes are analyzed through numerical simulation and are then compared with those from simplified simulation models. Simulation results show that at frequencies lower than the natural frequency of the first bending vibration mode, the coupled system vibrates under the hull-beam mode, and the shafting follows the hull. Near each natural frequency of the shafting, a vibration mode of hull structure also appears, and, therefore, the propeller-shafting's vibration can be transferred to the hull structure effectively. If the mass and cross-section area moment of the hull are far larger than those of shafts, and when the vibration modes of propulsion shafting are the only research subjects, the hull structure can be treated as a rigid body with little error. However, the coupled vibration mode and the shafts' anti-phase vibration mode may not be correctly reflected.