Ticari bir aracın kabin içi ses seviyesinin azaltılması için vibro-akustik modelleme

The interior noise inside the passenger cabin of automobiles can be classified as structure borne or airborne. In this study, the structure-borne noise which is mainly caused by the vibrating panels enclosing the vehicle was investigated. Excitation coming from the engine causes the panels to vibrate at their resonance frequencies and these vibrating panels cause a change in the sound pressure level (SPL) and undesirable booming noise. In order to improve the SPL in the cabin, it is critical to understand the dynamics of the vehicle and more importantly how it couples with the air inside the cabin. A combined usage of two methodologies was adopted in order to predict the sound pressure level inside the passenger cabin of a commercial vehicle under the effect of engine disturbances. Those methodologies are the Finite element method (FEM) for the structural analysis and the Boundary Element Method (BEM) for the acoustic analysis. The adopted FEM-BEM approach takes advantage of the Modal Acoustic Transfer Vector (MATV) algorithm that combines the Acoustic Transfer Vectors (ATV) with the normal structural velocity boundary conditions. MATV algorithm allows the calculation of acoustic contribution of each individual structural mode. This procedure uses a vector product to calculate the sound pressure and it is computationally very efficient. Another analysis which uses the ATV concept is Panel Acoustic Contribution Analysis (PACA). PACA enables the user to determine the contribution rate of each radiating panel to the noise level inside the cabin. The results of MATV and PACA analysis can be utilized to improve the design of the cabin components to eliminate the critical structural modes and also to reduce the contribution of the radiating panels to the interior noise level. Finally, the idea of using a Helmholtz resonator in the cabin was studied to reduce the sound pressure levels. A hole is placed on the bulkhead of the vehicle to make it behave as a Helmholtz resonator. The location and size of the hole were altered to see the effect of the hole dimensions and position. First, the analysis was performed on a simple rectangular box to determine the optimum location and size of the hole. Then, the analysis was repeated on the vehicle model that was used throughout this thesis. The results show that the hole on the bulkhead behaves as a Helmholtz resonator and improves the SPL at certain frequencies. However, it introduces another cavity mode and this additional mode can make the SPL worse at other frequencies.