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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.

Using finite element methods, an exhaust system's design can be optimized for weight and cost considerations. The optimization process involved the initial modeling of the system, the determination of an accurate loading system and the iterative analysis of trial designs. A static, gravitational loading was initially applied to the structure. A dynamic loading was then applied, using sinusoidal displacements at the exhaust system's support points. The optimizations resulting from the dynamic and static analyses yielded structures with 22% and 25% reductions in weight, respectively.