Stiffness optimization of marine propulsion shafting system by FRF-based substructuring method and sensitivity analysis

The present work is concerned with a dynamic modeling and optimization method to minimize the vibration transmission through the marine propulsion shafting system by the FRF-based substructuring method and the sensitivity analysis. The dynamic model of the coupled propeller - propulsion shafting - hull system under propeller exciting forces and excitation forces from the propulsion electric machine is established. Vibration response characteristics for the coupled system are analyzed. Mean-square forces and power flow transmitted to the foundation is employed as objective functions to evaluate the optimal design of propulsion shafting system. The proposed method can take into consideration of real propellers as well as the fluid-structure interaction between the propeller, hull and the surrounding water. It is shown that propeller flexibility contributes obvious peaks in the vibration responses. For the studied model, the stiffness of the bearings and the isolators should be lowered; the stiffness of the coupling should be increased to suppress vibration transmission. The mean-square force and the power flow transmitted to the foundation in the concerned frequency range is decreased to 0.712 and 0.525 of the initial value, respectively. The proposed dynamic modeling and optimization method is capable of performing optimization with greatly improved efficiency.