Studies On Sound Visualization Method Of Moving Vehicles

With current acoustic camera systems, noise sources can be identified and located quickly and intuitively. But because of the Doppler Effect of the noise of moving vehicles, it's difficult to apply these systems directly in the sound visualization of moving vehicles. Besides, there are some inconvenient or inaccurate procedures when these systems used on moving vehicles, which make the measurement inefficient. Therefore, the researches on the method that makes sound visualization of moving vehicles more intuitively, quickly, and accurately have very practical significance.First, the mathematical descriptions are created for all kinds of the engineering objects in the sound visualization of moving vehicles, including the coordinate systems for the graphic and spatial postions, and their transformations. The sound fields are defined, such as the source field, the measurement field, and the reconstruction field, and their temporal and spatial relationships are desribed.The binocular vision method for acquiring the vehicle pictures with the ground positions is proposed. The pictures of the moving vehicle are shot by two cameras separately, and the screen positions of the location marks stuck on the side surface of the vehicle are identified. The same marks are matched with identifying the serial numbers of the marks, and the spatial positions of the marks can be computed with binocular vision theory, then the position and the velocity of the moving vehicle are acquired.The method of restraining the ghost sources for the moving source sound field is proposed. The short-time wave superposition relation for moving sound sources is deduced by analyzing the Doppler Effect in very short time. The source strengths of the point sources in the source field are pre-estimated with the beamforming algorithm, and the possible main sources are identified with the pre-estimation result. Then the wave superposition equation for the main sources is founded, and the source strengths are figured out by solving the equation. At last, the sound pressure distribution of the reconstruction field is computed with the source strengths.The sound field and the pictures are temporally synchronized by collecting the sound pressure and the camera trigger signal at same time and analyzing the saved trigger signal. The sound field and the pictures are spatially matched with the coordinate transformation between the ground coordinates and the screen coordinates of the reconstruction points. Then the sound field and the pictures are merged with the mapping from sound pressure to color, and the dynamic sound field video is finally generated.The hardware and software system of the sound visualization of moving vehicles with the above method is developed, and the procedure of the test is established. The visualization tests with known sound sources and real vehicle noises are carried out to verify the performance of the system. The results of the tests indicate that the sound visualization of moving vehicles can be realized correctly and conveniently with this system. Then, the main noise sources can be identified with the analysis to the reconstruction video intuitively, and the changes of the sound field in the moving process can be represented.