Modal Analysis on an Exhaust Manifold to define a Catalyst FE-model

Abstract: Faurecia Exhaust Systems AB develops and manufactures exhaust manifolds for the car industry. In the developing process the FE-models are one of the main tools and they are becoming more and more important in the automotive development. In the tough competition between the manufacturers, the demands for fast development require good FE-models both from the manufacturers and their subcontractors. The main goal of this thesis is to update an existing FE-model of a close coupled exhaust manifold and look at the catalyst to investigate the behavior of the catalytic converter and suggest a way to model the monolith. The thesis combines analytical calculations with experimental measurements. By the use of modal theory, an analytical model is updated to resemble the experimental data. The results of this thesis work include a description of an updated version of the FE-model of the exhaust manifold. It also includes one example of how to model the catalyst assembly. The model of the catalyst assembly has been validated. The initial Finite-Element model showed relatively large differences for the first four natural frequencies, when compared to experimental data. Relatively large amplitude errors were also obtained when comparing frequency response function from the experiment and the model. An acceptable error was obtained for the natural frequencies when comparing the experimental result and the updated Finite-Element Model. The updating was mainly done by changing the mass and stiffness in the welds and the converter tube.