Vibroacoustic Coupling of Cylindrical Structure with Both Excited End Plates
Vibroacoustic coupling phenomena occur in a variety of different situations and are generally studied with the goal of controlling noise. However, we also expect that they are applied to new technologies based on energy stored in each system. In this study, we investigate vibroacoustic coupling between structural vibrations and the internal sound fields of thin structures. We consider a cylindrical structure with thin plates at both ends and investigate the coupling between the plate vibrations and the internal sound field when external periodic forces are applied to respective end plates. This coupling is theoretically and experimentally investigated by considering the behavior of the both plates and the acoustic characteristics of the internal sound field with variations in the periodic forces. In the analytical model, the end plates are supported by springs in circumference to make those support conditions close to actual conditions in the experiment due to adjustments of spring stiffnesses, and then the cylinder is assumed to be structurally and acoustically rigid at the lateral wall between the structure and the sound field to simplify this problem. The acoustic characteristics are evaluated by the sound pressure level, which is maximized with changing the phase difference between the both plate vibrations, when the phase difference and relative amplitude between both periodic forces are varied. The behavior of the plate vibration is studied from changing the phase difference with the cylinder length. In comparison between characteristics of the both systems, it is clarified that vibroacoustic coupling is effective in increasing acoustic energy and the phase difference depends greatly on the acoustic mode, which contributes the formation of the sound field.
Radiation of sound into a cylindrical enclosure from a point-driven end plate with general boundary conditions
The radiation of sound from a point‐driven circular plate into a hard‐walled cylindrical enclosure is investigated. Emphasis is given on studying the effects of the boundary conditions of the plate, which are modeled as a continuous distribution of edge springs acting against both the deflection and the rotation of the contour of the plate. With this model, both classical and intermediate boundary cases can be simulated by adjusting the elastic stiffness of the springs. A coupled acoustoelastic formulation is developed following a variational approach, with the use of hard‐walled cavity modes. In the analysis, the full interaction between the structure vibration and the internal cavity sound pressure is considered. Numerical results indicate that a significant reduction in noise inside the cavity can be obtained for a relatively wide frequency range by completely relaxing the translational support (zero deflection stiffness) of the plate. This is mainly due to a weakening of the modal radiation efficiency...
The effect of continuous exposure to low frequency electric fields on three generations of mice: A pilot study
Mice were allowed to mate, gestate, deliver and rear their offspring for 3 successive generations while being continuously exposed to 60 Hz electric fields. Mice exposed to vertical electric fields exhibited decreased body weights at 35 days postpartum and increased mortality, rates for 3 successive generations. Mice exposed to horizontal electric fields exhibited decreased body weights for 2 successive generations.