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Hydraulic engine mounts are widely used in aerospace and automotive applications for vibration isolation. Here in this paper an active engine mounting system is proposed which not only acts like an isolator in a wide range of frequencies, but also performs as a damper when shock inputs and engine resonances are present. The proposed new design consists of a conventional passive fluid mount, an electromagnetic actuator (voice coil) and a capacitive circuit. The voice coil is placed in the lower chamber of the passive fluid mount and it can change the volumetric stiffness of the bottom chamber actively such that the mount has low dynamic stiffness in a wide range of frequencies. The capacitive circuit is paralleled with the voice coil and in situations when large shock inputs are present; it adds capacitance to the electromagnetic circuit and changes the characteristics of the mount from an isolator to a damper. Here in this paper the physical and mathematical models of the new mounting system are presented, the simulation results are shown and the performances of the proposed design in all active, passive and damper conditions are demonstrated.

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Due to the importance of acoustic response control of submerged vibrating structures, in this study,the optimization of acoustic power radiation from a square stiffened plate under harmonic loading was investigated.Since one face of the plate is in contact with water, a fully coupled analysis was used. The effect of fluid in the analysis was considered via added mass matrix. The added mass matrix was obtained based on both Rayleigh integral and the boundary element approaches.The obtained added mass matrix was then added to the mass matrix of the structure calculated from the finite element discretization of plate. Several variables such as acoustic pressure at specific points and also radiated power were calculated. Results show good agreement between obtained results from the Rayleigh integral and the boundary element. To reduce the radiation power, dynamic absorbers in the form of lumped mass and mass-springs in specific locations on the plate surface were considered. Because optimization procedure requires several evaluation of cost function in the design variable space, model reduction can save a great amount of computation efforts. Therefore, the truncated modal matrix was employed and its effectiveness and precision on the obtained results was studied. Finally, Genetic Algorithm (GA) was used for minimizing the appropriate goal function in three case studies: concentrated mass on cross-points, dynamic absorbers on cross-points and combination of two former cases.All the studied cases resulted on significant reduction in the goal function index.