Automobile vibrations and acoustic noise reduction via modal analysis technique

Mechanical vibrations of vehicle exhaust system can cause cabin and environmental noise as well as structural durability concerns. The environmental noise impact due to the high traffic intensity in the urban areas has become a critical concern and considerable amount of calmness are required. Also, the ride comfort is one of the most important objectives of vehicle designers and manufacturers. Automobile noise is complex and has various sources. These sources are engine intake and exhaust noise, drive train, tire noise, and chassis noise. Automobiles are subjected to strict restrictions on intake and exhaust noise based on their displacement and weight, leaving very little options for further noise reduction. In order to develop noise countermeasures under these conditions without resorting to a short-term schedule trial-and-error development, and because noise reduction goals cannot be met by simple extensions of development methods, efforts are now being directed toward new fundamental technologies. The exhaust system is mainly consists of pipes and mufflers. Mufflers as main part of this system are the scope of this paper. Mufflers, which are classified into absorptive and reactive, have many applications; one of them is the vehicle exhaust system. Fibrous and porous materials are used to absorb the noise and vibrations. Noise reduction can be achieved fibrous or porous materials in the absorptive mufflers. While, reactive mufflers are manufactured from conventional materials depends mainly on their geometries. Muffler cylinders with double skin of circular and elliptical shapes were proposed and investigated and compared with the single layer skin cylinders in this study. A method for vibration and vibration-acoustical modelling and evaluation of exhaust systems mufflers boxes was proposed. In this method Finite Element analysis was done to predict the vibration and acoustic noise of muffler systems, and experimental modal analysis was done to measure and extract the natural frequencies, modal damping and mode shapes of the some muffler boxes. Dual channel signal analyzer equipped with computer and modal analysis software. The double skin mufflers with a suitable gape between layers present a good solution for noise vibration and noise reduction. The method provides rigorous framework for exhaust system muffler model creation and verification, as well as analysis and postprocessing.