This Thesis is focused on the development and implementation of efficient methods for the acoustic modeling and design of exhaust mufflers for internal combustion engines, by means of tools based on analytical and numerical solutions of the governing wave equation. There is an increasing need for design techniques that lead to fast, accurate and reliable results even in the high frequency range, due to the fact that vehicle noise has become one of the major sources of environmental pollution.
The main core of the Thesis deals with the extension and application of the Mode Matching Technique, in combination with a novel Substructuring Method, to compute the acoustic attenuation of exhaust dissipative mufflers. A relevant contribution is associated with the computation of the transverse eigenfunctions of the muffler, for which a new technique has been developed and successfully applied to dissipative mufflers that include fibrous absorbent material. 
In addition, relevant muffler components have been measured experimentally to provide accurate data, such as the perforate impedance and the bulk properties of absorbent materials. The models found in the literature have been validated or improved with these measurements.
Several methods have been evaluated for the characterization of absorbent materials. As a conclusion, it has been found that there are not substantial differences between these techniques. The most suitable approach is the two-source method since the results are independent from the condition downstream the sample. Two materials have been characterized by this technique, and the parameters of the Delany and Bazley semi-empirical model have been fitted. In addition, the two-source method has been used for characterizing perforated elements, fitting the experimental results to the Sullivan’s model.
To perform the acoustic analysis of dissipative mufflers, the Mode Matching technique has been extended to the case of absorbent materials in combination with a Substructuring Method to calculate the transversal pressure modes. To define the material, a model based on two parameters –impedance and wavenumber– has been used. The Substructuring Method has been preferred because it is versatile and presents less mathematical problems in comparison with the Direct Method in obtaining the natural frequencies and the corresponding modes.
Several geometries of mufflers have been experimentally tested to validate the models developed in the Thesis. Finally, a specific configuration has been analyzed to show how the relevant parameters of the design –including absorbent material– have an influence on the muffler.