Acoustic wave propagation and attenuation in catalytic converters are investigated in the present study. The relationships for wave propagation in a catalytic monolith are derived first and then coupled to the wave propagation in tapered ducts which are commonly placed at either end of the monolith. Analytical and finite element approaches are used to solve the resulting coupled system of equations. Theoretical predictions are then compared with the experimental results for two different (one circular and the other oval) catalyst configurations. The attenuation characteristics of the catalyst with and without the monolith are also investigated.
Resonant sound absorbers are used widely as anechoic coatings in underwater applications. In this paper a finite element scheme based on the Galerkin technique is used to analyze the reflection characteristics of the resonant absorber when insonified by a normal incidence plane wave. A waveguide theory coupled with an impedance matching condition in the fluid is used to model the problem. It is shown in this paper that the fluid medium encompassing the absorber can be modeled as an elastic medium with equivalent Lamé constants. Quarter symmetry conditions within the periodic unit cell are exploited. The finite element results are compared with analytical results, and with results published elsewhere in the literature. It is shown in the process that meshing of the fluid domain can be obviated if the transmission coefficients or reflection coefficients only are desired as is often the case. Finally, some design curves for thin resonant absorbers with water closure are presented in this paper.
The classical two-duct Herschel–Quincke tube is generalized to an n-duct configuration. A closed-form expression is developed for the transmission loss characteristics, as well as for the resonance locations. While the results are illustrated in the present study in terms of three-duct configurations alone and in comparison with the two-duct arrangements, the developed expressions hold for any number of ducts and cross-sectional area combination.
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