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Réduction des niveaux vibratoires d'un panneau au moyen de trous noirs acoustiques structurés en réseau périodique : conception d'une méta-plaque

Abstract : Because of the inconvenience they cause, the vibrations of the mechanical structures are an important subject of study in many industrial contexts. The passive reduction of the undesirable vibratory levels is generally obtained by the addition of viscoelastic materials, granular materials or dynamic absorbers. These efficient and relatively simple methods of implementation give rise to an added mass, which is generally not desired. The Acoustic Black Hole (ABH) is an alternative strategy, allowing the structures to be damped passively without increasing their mass. The ABH consists of performing a local thinning of the structure and coating it with a thin viscoelastic layer. The ABH effect then results from the local increase in the vibratory amplitude, which strongly stresses the viscoelastic coating, giving rise to high localized damping. The general objective of the thesis work is to carry out a detailed analysis of the damping mechanism induced by the ABH, in order to make the most use of it. A black hole without a viscoelastic coating, inserted into an infinite thin plate is initially analyzed by means a wave model. The analysis of the dispersion relations shows that four bending waves coexist in the inhomogeneous region and that, beyond a cutoff frequency, all these waves are strongly attenuated, thus reflecting the ABH effect. The study of the scattering cross-section shows that there are local trapped resonances, and that it is possible to control them by means the geometric characteristics. The ABH with viscoelastic coating is studied using a finite difference formulation. It is shown that the addition of the viscoelastic film induces an important local damping mechanism, allowing to significantly increase the overall damping of the structure. The ABH effect being especially effective beyond its cutoff frequency, we propose the design of a meta-plate, consisting of a periodic distribution of a set of black holes, so as to take advantage of possible low frequency Bragg or resonance band gaps. A square periodic lattice is studied numerically by the PWE method and experimentally by measurement of vibratory mobilities. The analysis of the dispersion diagrams shows that it is difficult to obtain complete band gaps at low frequencies by using the classical ABH. The measurements confirm this finding: the mobilities are only smoothed in the high frequency range, reflecting a cumulative effect of the different black holes. Another strategy is to use a periodic rectangular or triangular lattice of black holes with sinusoidal profiles. The plate is analyzed numerically and experimentally and the results show that the meta-plate is both damped at low frequencies by the lattice effects and at high frequencies by the cumulative effects of black holes,which makes an interesting structure for the engineer.
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Submitted on : Monday, February 26, 2018 - 4:48:24 PM
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  • HAL Id : tel-01717745, version 1

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Omar Aklouche. Réduction des niveaux vibratoires d'un panneau au moyen de trous noirs acoustiques structurés en réseau périodique : conception d'une méta-plaque. Vibrations [physics.class-ph]. Le Mans Université - LAUM - Le Mans (72), 2017. Français. ⟨NNT : 2017LEMA1030⟩. ⟨tel-01717745v1⟩

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