Desenvolvimento de análise por trajetórias vibroacústicas para aplicação automotiva

Abstract

An analysis and development of how vibration and acoustic noise generated in a motor car arrives at the interior of the vehicle, a key issue in modern industry, is presented. The study considers the development of experimental techniques, employing computational data processing and data systemising, leading to the identification and ranking contribution of both airborne and structure-borne paths. Identification of the two previously mentioned types of path is the focus of the present work, which has been studied, with the help of a purposed build physical) prototype. This prototype simulates a typical motor car and enables coupling and decoupling of the two paths. This procedure has provided an insight into the spectra provided by the individual contribution of structure and air borne paths, The spectra correlation involved the study of Multiple Inputs / Single Output Systems, or MISO has been developed with the use of Multiple Coherence Functions (MCF) in order to identify Frequency Response Functions (FRF), by means of mutual correlation between stimuli and the correlation between stimuli and response. The decomposition into singular values has been used to compensate the effect of the coherence among the stimuli. The computational development using the classical TPA (Transfer Path Analysis) method has also been implemented for the developed prototype, again with the objective of structure and airborne contributions. TPA requires essentially two sets of information: 01) Mechanical Force FRF between application point (source) or acoustic force (volume velocity) reaching the receiver, and 02) the indirect estimation of the operational forces (both mechanical and acoustical) obtained with the prototype under normal operational conditions. The use of the (indirect) method of matrix inversion has proved to be crucial for the estimation of the operational forces, given the difficulty for the use of direct techniques and the consequent loading effects. The two methods (MISO and TPA) could be mutually compared with the results obtained from the Physical isolation of the paths. The measurements and final results are discussed in detail and how they relate to actual real.