Cavity Analysis And Research Of The Internal Sound Field

With the development of automobile industry, especially in terms of high power, high speed and light weight of automobile in recent ten years, the vehicle noise problem has already drawn high attention of the related departments both at home and abroad. It has become one of the hot issues in the vehicle research on how to improve the acoustic environment both inside and outside vehicles, reduce the level of vehicle interior noise and develop the ride comfort. The statistical energy analysis (SEA), finite element method (FEM) and boundary element method (BEM) are combined to make analysis and research in the whole frequency for a simple cavity with the forced vibration. The main research contents and innovations are as follows:In the aspect of SEA, firstly the model of the simple cavity is established based on the SEA principle; the characteristic equations of the cavity interior sound field are deduced and the response value at one frequency point in the high frequency range is calculated. Then the interior sound field character in the whole frequency range is stimulated and analysed by using the analysis software based on SEA. The simulation analysis results, calculated values and former experimental values are compared. The results demonstrate that SEA is suitable for the research of vibration and noise in the high frequency range, while in the low frequency range the results have a fairly big error and sometimes are even incorrect. In addition, the coupling losing factor between the cavity out wall and the interior liquid has a slight influence on the sound field response.With repect to FEM, the cavity model based on FEM is built; the liquid-solid coupling model equations are deduced; and the sound field characteristic inside the cavity is analysed by means of the analysis software based on FEM. The analysis shows that the calculation results from several different points have great differences when compared for the reason that the results calculated from FEM refer to the responses of the specific points (field points) under different frequencies; the responses of all the nodes must be calculated for FEM before the field point results are calculated, thus the strong computing capability and the large storage space are needed; and the calculated and analysed results by FEM in the low frequency range are accurate enough to precisely reflect the resonant frequency and value of the response, but with the increase of the calculation frequency, the computing cost is notablely increased and the reliability of the computing results are becoming worse.The application range of BEM is also the low frequency range through analysing its calculation results, but the two-dimentional element calculation is used by BEM to substitute for the three-dimentional element calculation of FEM so as to greatly reduce the requirement of computational performance. The error between the results calculated respectively by BEM and FEM is below 1%, thus BEM is more reasonable than FEM during calculating the noise questions of the enclosed sound field.The sound field characteristic inside the cavity is achieved under the whole frequency in the one-third octave band, providing reference for investigating the models in practical engineering, and facilitating analysing the influence of various factors on the response in practical systems.