Numerical Study on Nonlinear Isolation of Vibration Transmission from the Ship Propeller Shaft to the Deck Plate

Vibration-induced noise in a ship structure can be caused due to propeller shaft vibration. This vibration can cause problems for the passengers on a cruise ship. This study aims to develop a nonlinear model for a propeller shaft vibration and understand the effectiveness of a nonlinear isolator in reducing the vibration amplitude. The vibration from the propeller shaft is transmitted to the deck plate. The coupled system of the propeller shaft and the deck plate is modelled as a two-degree-of-freedom system. The propeller produces high response due to synchronous whirl and instabilities such as oil whirl and dry whip. In order to incorporate the nonlinear modal interactions, the propeller shaft is modelled as a nonlinear duffing oscillator. Vibration from the propeller shaft is transmitted to the deck plate. The deck plate is modelled as a spring mass system having coincident frequency with the synchronous whirl frequency. The propeller shaft is coupled using a linear and nonlinear isolator to the deck plate. Vibration isolation devices are used to protect systems from unwanted vibration force or displacement, positioned between the source of the disturbance and the equipment that has to be protected. The study aims to understand the isolator's influence in controlling the vibration transmitted to the deck plate. Two types of isolators are considered in the study linear and nonlinear isolators. The passive nonlinear isolator is modelled as a cubic spring which induces a high static and low dynamic stiffness. The nonlinear coupled two-DOF system is solved using the harmonic balance method and compared using numerical continuation. The result from the study indicates that the nonlinear isolator effectively reduces the vibration on the deck plate.