DESIGN OPTIMIZATION OF MARINE ENGINE-MOUNT SYSTEM

Design optimization of marine engine–mount system for vibration control is presented in this paper. The engine is modelled as a rigid body with supports connected to a rigid floor. The mounts are modelled as three-dimensional isolators with hysteresis damping. The objective is to select the stiffness coefficient and orientations of individual mount in order to minimize the vertical force transmitted from the engine to the floor to control the structure-borne noise. Constraints are imposed to keep the isolator static and dynamic deflection within the desired limits and a minimum gap between system natural frequency and engine excitation frequency for avoiding possible system resonance. The sequential quadratic programming (SQP) technique has been applied as the optimization algorithm. The typical force and moment of a 4-stroke engine with one cylinder is analyzed and input in the optimization system. The results of optimization are compared with that of a conventional engineering design with the isolators working under their maximum allowable deflection. This comparison shows that, as compared with force transmission of the conventional isolation system, the value of optimized system is only half for multi-frequencies excitation and one-fourth for single frequency excitation. The mechanism of vibration isolation involved in the optimization is investigated with the frequency response of the system. Sensitivity study of the system with the variation of the design parameters is also carried out and proves that the minimum obtained is the global value in the range of design parameters.