The energy transmission in a mechanically linked double-wall structure into an acoustic enclosure is studied in this paper. Based on a fully coupled vibro-acoustic formulation, focus is put on investigating the effect of the air gap and mechanical links between the two panels on the energy transmission and noise insulation properties of such structures. An approximate formula reflecting the gap effect on the lower-order coupled frequencies of the system is proposed. A criterion, based on the ratio between the aerostatic stiffness of the gap cavity and the stiffness of the link, is proposed to predict the dominant transmitting path, with a view to provide guidelines for the design of appropriate control strategies. Numerical results reveal the existence of three distinct zones, within which energy transmission takes place following different mechanisms and transmitting paths. Corresponding effects on noise insulation properties of the double-wall structure are also investigated.

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Acoustic modes and the coupling characteristics of a rectangular-like cavity with a slight geometrical distortion introduced through a leaning wall are investigated in this paper. A pressure variation index is proposed to quantify the global changes in acoustic modes caused by the inclination of the wall. Effects on the coupling between acoustic modes and structural modes are investigated using coupling coefficients. Numerical results show a simple relationship between the distortion effect and the acoustic wavelength. The effect is most significant when the distortion approaches the half wavelength. Compared with a rectangular enclosure, the existence of the leaning wall gives rise to a much more effective coupling between the structure and the enclosure.

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In this paper, the numerical modeling of a damaged plate with piezoelectric actuation is presented. Unlike in previous studies, the effects of the defect are considered and embodied by mass and stiffness reductions in the equation of motion. The model is validated using indices related to frequency variation and energy change in both frequency and time domains. A comparison of the tendencies of the measured indices with those of the simulated ones shows a reasonably good agreement. Results show that the energy index is more sensitive to damage than the frequency index. Both square-wave and pseudo-random excitations can be used to assess the energy index variation. For the latter, however, an averaging over time signals is needed to provide more reliable results.