| The noise is a kind of voice that makes people irritate. If the volume of noise istoo strong, it will be harmful to human health. With the accelerating of the process ofindustrialization of the modern society, high speed, high-power devices are increasing.The noise generated by the equipment gradually attracted people’s attention. Noisepollution can be identified as one of the four environmental pollution. With theimprovement of the people’s material conditions and living standards, people’srequirement of their own surroundings become higher and higher. Automotiveproducts are required to be more quiet, comfortable, fun to drive, which are closelyrelated with the car noise and vibration control. How to reduce the noise has becomean important research in the field of noise control.Noise is generated by the object vibration. The control of noise can be roughlyfrom two aspects: the one is to reduce the vibration of objects, the other is to use ofsound absorption. In order to reduce the structural vibration and control the radiatednoise of shell pieces, the structural-acoustic optimization problems of shell piecesbased on structure-acoustic sensitivity analysis are researched in this thesis.The main research works of the thesis are as follows:(1) The basic theory to solve structural-acoustic problems by combing finiteelement and boundary element method is introduced；The formulas for calculation thestructure-speed sensitivity, speed-sound pressure sensitivity, speed-sound powersensitivity are derived；The basic theory and analysis method for the follow-up tosolve engineering problems are provided.(2) The middle faces of oil pan in a micro-car were extracted from the softwareUG, and then they were put into Hypermesh software by iges format to generate finiteelement mesh. Modal parameters and modal sensitivity of shell pieces are calculatedby Nastran.The surface vibration velocity distribution was analysed through applyinga known load on the shell. The results showed that the velocity distribution wasuneven, some areas of the oil pan have a larger vibration, and these areas willcertainly have a greater noise.(3) The structure-velocity sensitivity of shell pieces was calculated by Nastran,and the result was imported into Sysnoise. Then the boundary element model wasestablished by associating the shell model with structure-velocity sensitivity of shell pieces. Structure-pressure sensitivity and structure-sound power sensitivity wereanalyzed. Acoustic responses of each excitation frequency were obtained and it wasfound out that the response peaks of model appeared obviously in1000Hz,1500Hz,2000Hz.(4). The shell model was optimized by software Isight integrating Sysnoise andNastran based on structural-acoustic sensitivity analysis. Structure-acousticoptimization design under single point multi frequency excitation, light weight designunder multi frequency excitation and multi objective optimization problem undermulti frequency excitation were studied respectively, and different optimizationresults were obtained. It’s shown that the optimized model has better acousticperformance through contrasts of contour.In this thesis, the oil pan shell of a mini car was taken as the actual researchobject. It was researched from the aspects of modal analysis, modal sensitivityanalysis, surface vibration characteristics analysis under engine excitation, designdomain points sound pressure analysis and structural-acoustic sensitivity analysis ofdesign domain points. The design optimization process was established in order toreduce the peak value of sound pressure level in design domain points by means ofmodifying the oil pan shell structure parameters based on structural-acousticsensitivity. Research works proves that shell pieces radiation noise control methodbased on the structural-acoustic sensitivity analysis was effective. |
PDF Full Text Request