Diffusion multiple en fluide visco-thermique, cas du cristal phononique à deux dimensions

Abstract : An accurate modelization of acoustic waves propagation and absorption by porous media is of great interest notably due to their numerous applications in industry. During the past years, important progresses lead to acoustic behavior description of porous media in the long wavelength domain (audible frequencies) by means of classical homogenization theory. In this domain, the description is assumed considering important visco-thermal effects which occur inside the medium and so, gives its absorption ability. When the wavelength reduces enough (ultrasonic frequencies), multiple scattering effects appear due to interactions between microstructure and acoustic waves. These effects are not considered by classical models owing to geometrical complexity of porous media at microstructure scale.

For this reason, the study is restricted to the case of a two-dimensional periodic lattice containing rigid cylinders (aluminium) surrounded with a visco-thermal fluid (air). This simple geometry, also called "phononic crystal", can exhibits frequency regions where propagation is forbidden (band gaps). This well known phenomenon arises from multiple scattering effects (interferences). Band gaps locations and widths are predicted by many numerical methods taking into account multiple scattering without dissipation. In this work, the sizeable consideration of dissipation effects are discussed. Extensions of multiple scattering models allowing for visco-thermal effects are introduced. On the one hand, these extensions underline dissipation effects impact on propagation at high frequencies. For that, comparisons are performed between transmission coefficients theoretically predicted and experimentally measured on different samples. On the other hand, a numerical study on the transition between a visco-thermal regime (entirely) and multiple scattering effects emergence when wavelength reduces is carried out. This analysis points out the high frequency limit of classical homogenization theory for porous media characterization.
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Acoustique [physics.class-ph]. Université du Maine, 2007. Français
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Aroune Duclos. Diffusion multiple en fluide visco-thermique, cas du cristal phononique à deux dimensions. Acoustique [physics.class-ph]. Université du Maine, 2007. Français. 〈tel-00305480〉



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