Dynamic research on nonlinear vibration mechanism and control method for marine parallel propulsion system

The marine propulsion system with parallel engines is commonly employed in high-power ships. However, the manifestation of vibration instability and induced rattle phenomena of the main gear present significant challenges to the reliable operation of the propulsion system. This paper elucidates the underlying dynamic mechanism and proposes effective vibration control strategies for the primary components subjected to vibrational influences. To accomplish this, a nonlinear dynamic model that considers lateral-torsional-longitudinal coupling of the propulsion system is established, based on the analysis of both internal and external excitations. The effects of various combinations of dynamic parameters on the vibration response of the system are systematically examined through theoretical simulation and experimental investigations. Subsequently, a magnetorheological fluid (MRF) control unit is introduced to mitigate the torsional vibration of the main gear-rotor system. It is observed that when the MRF unit is positioned far away from the main engine, the vibration amplitude can be reduced to less than 50% of the value when MRF is not used, and the equilibrium position of the torsional vibration approaches zero. The research results are expected to provide a theoretical foundation for addressing the technical challenges associated with enhancing stability and reducing vibration in such systems.