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Sound transmission through a cylindrical double-walled shell lined with an elastic porous material is studied. Love's equation is applied to describe the shell motions coupled with acoustic wave equations. An interesting method is developed to simplify the analysis of the wave propagation in the elastic porous material, which reduces the model developed by Bolton et al. [2] based on the Biot's theory [1] to a simple one-dimensional wave propagation model. The results from the simplified model are compared with those from the Bolton's model and measurements. Solutions for the sound transmission through the cylindrical double-walled shell lined with an elastic porous material are obtained for various configurations using the simplified method, and compared with measured results. Advantages and limitations of the simplified analysis method developed are explained from the perspective of practical applications.

Sound transmission through the sidewall of an automotive muffler has been studied theoretically and experimentally. Three wall structures: a single shell, double shell and porous-cored shell constructions are considered. Transmission losses through the sidewalls were measured using the two microphone method. Experimental results are compared to one another, and to the corresponding theoretical analysis results, which shows that the mean flow effect is not a significant factor in designing the muffler sidewall.

An experimental method to identify damping characteristics of a dynamic system is reported. The method identifies damping matrices of the equation of motion of the system from measured frequency response functions, each different damping mechanism in a distinct matrix. Related experimental techniques and signal processing issues are discussed. Theoretical validation and error study are conducted by applying the method to a theoretical example. The method is applied experimentally to a thin beam with two different damping characteristics for experimental validation and demonstration of the method. Important advantages of the method over existing methods are explained.