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The use of computer calculation tools in order to reduce the cost of the development of optimized exhaust systems has turned out to be a generalized industrial practice. Therefore, considerable efforts are devoted to the development of suitable calculation tools, which are representative of the real phenomena taking place in the exhaust systems. In the present paper, the results of the application of a hybrid linear/nonlinear calculation method to the prediction of the exhaust noise radiated by I.C. engines are presented. First, a brief description of the method is given. Then, comparison is shown between the results of the calculation and experimental measurements, both for in-duct pressure and for noise radiated. The agreement obtained indicates that this method may be used as a design tool in the frame of the new methodologies presently arising in exhaust system development.

Concentric perforated duct mufflers are broadly used when designing automotive front mufflers because of their acceptable acoustic performance and their low backpressure. In the frame of the design methodologies presently used, suitable theoretical models are needed in order to estimate this performance without the need to build prototypes and perform experimental tests. A lot of work has been performed in this sense; nevertheless, there remains a reasonable doubt that the results obtained with purely linear models are representative of the muffler behaviour under actual engine conditions. In the present paper, a two dimensional finite element model is used in order to compute the transmission loss of several concentric perforated duct mufflers, and the results are compared with experimental measurements performed with a modified version of the impulse method that allows for the use of high amplitude pressure pulses as excitation.