Vibration analysis of the propulsion shaft system considering dynamic misalignment in the outer ring

Propulsion shaft systems play a crucial role in marine applications, particularly in ships and underwater vehicles. However, existing research often overlooks the dynamics involved in the transmission of vibrations from the bearing to the housing and subsequently to the hull, which affects vibration control in marine equipment. Therefore, this study introduces an enhanced dynamic model for a propulsion shaft system, incorporating the dynamics of the bearing outer ring and housing. The proposed model deduces the deformation relationships between the ball and the inner/outer ring, considering the outer ring translation and swing. The contact force between the outer ring and bearing housing is calculated using conformal contact theory. Timoshenko beam theory is used to develop the shaft dynamic model, while the propeller, bearing components, and bearing housing are represented through the lumped parameter method. To validate the proposed model, an experiment is conducted, demonstrating its accuracy. The study provides analysis of the bearing contact force, shaft dynamics, and bearing housing dynamics. Additionally, the influence of bearing clearances on the shaft and bearing housing dynamics is investigated. The results show that controlling bearing #2 clearance to below 20 μm helps reduce the system vibrations.