Aiming at improving the structure of torpedo engine, the damping technology based on modal contribution method was proposed. Based on the results of the linear combination analysis of the modal participation factors, the vibration control method of the constrained damping layer was designed to control the dominant modes with large contribution. Firstly, the dynamic model of torpedo engine support structure is built, and the modal frequency, modal displacement and normalized modal stiffness are obtained. The dominant modes in the target frequency band are calculated, and the first 24 modes are analyzed. According to the mode shape of dominant mode, the constrained damping layer is designed for the engine. The optimized structure was verified by numerical simulation and the corresponding experimental results. The results showed that the damping technology based on modal participation factor can significantly reduce the vibration response of the engine support structure. This method creatively combines the dynamic design with the damping design, and obtains an effective damping method for engineering, especially for the military industry field with narrow space and strict weight requirements.

To explain the sudden jump of pressure as the variation of water depth for a direct-acting relief valve used by torpedo pump as the variation of water depth, a 2-DOF fluid-structure coupling dynamic model is developed. A nonlinear differential pressure model at valve port is applied to model the axial vibration of fluid, and a nonlinear wake oscillator model is used to excite the valve element in the vertical direction; meanwhile, the contact nonlinearity between the valve element and valve seat is also taken into consideration. Based on the developed dynamical model, the water depths for the sudden jumps of pressure can be located precisely when compared with the experimental signals, and the corresponding vibration conditions of the valve element in both the axial and vertical directions are explored. Subsequently, in order to eliminate the sudden jumps of pressure, different pump inlet pressure was tested experimentally; when it was decreased to 0.4 MPa, the pressure jumps ever appeared during the dropping and lifting processes were removed, and the numerical simulation based on the developed mathematical model also verified the experimental measurements.