Computational and experimental investigation of low frequency noise in passenger vehicles

Abstract

In this study, low frequency noise characteristics of passenger vehicles are addressed. Vehicle noise variability and dominant paths that cause low frequency booms are investigated. To diagnose the cause of variability, a systematic approach is proposed, where all steps are explained brie y. Current practice of experimental transfer path analysis is discussed in the context of trade-o s between accuracy and time cost. An overview of methods, which propose solutions for structure borne noise, is given, where assumptions, drawbacks and advantages of methods are stated theoretically. Applicability of methods is also investigated, where the engine induced structure borne noise of the sedan studied is taken as a reference problem. Sources of measurement errors, processing operations that a ect results and physical obstacles faced in the application are analyzed. E ects of damping, reasons and methods to analyze them are discussed in detail. In this regard, a new procedure, which increases the accuracy of results, is also proposed. Coupled vibro-acoustic response of the sedan is analyzed, and the e ect of folding rear seat aperture is studied. An analytical solution is proposed to calculate acoustic eigenfrequencies. Then, uncoupled acoustic eigenfrequencies of the actual cavity, where trunk and cabin cavities are connected through the aperture are computed. It is shown that planar acoustic eigenfrequencies of the sedan can approximately be calculated using the analytical solution proposed. To further clarify the impact of folding rear seat aperture, coupled vibro-acoustic response of the sedan is analyzed through di erent case studies. Experimental modal analysis studies are carried out to update the computational model. The updated model is then used in modi cation prediction studies.