Study On Prediction Of Radiating Noise And Structure Optimization Of Engine Part

Currently, motorcycles still occupy an important position in our traffic,however, the noise of motorcycles is becoming more serious. With theimprovement of people’s living standards, the motorcycle noise hasbecome the focus of attention. The engine is one of the source of themotorcycle, and the surface radiation noise of the engine is produced by thesurface vibration. The engine shell not only is a typical thin-wallcomponent, but also is the main part of the surface radiation noise. In orderto improve the research level of engine noise, the thesis takes an engineshell as a research object, and based on the theory of finite element methodand boundary element method. Using finite element analysis softwareANSYS and acoustic analysis software SYSNOISE as a simulation tool tostudy on the structure characteristics and acoustic characteristics of theengine shell parts, and verify whether the simulation results is correctthrough the sound intensity experiments.In this paper, according to the drawings and entity of the motorcycleengine shell, a solid model was built in the Pro/E software. Using thepre-processing software ANSA to mesh the solid model, build the finiteelement model and import it into ANSYS to analyze. The finite elementmodel was built by contrast the four kinds of cell size, finally, determinetaking the4mm unit size as the model to analyze and calculating thestructural natural frequency and vibration mode Etc. The results show thefirst six non rigid modal are bending modal, which take the important effectfor the vibration noise of structure surface. Using ANSYS to analyzetransient model, obtain the structure surface vibration response and extractthe response data of the surface node. Using acoustic analysis softwareSYSNOISE to calculate the vibration noise of the model, obtain thepressure distribution of the structure surface, the intensity contours of thefield point, sound pressure and intensity of the field point, etc. Using theAWA6290sound system determines the shell surface noise source and themeasuring point of the sound intensity spectrum. The results of noiseprediction and sound intensity experiment are show to be consistent; they proved that the analysis theory and method are correct and credible. Foundfrom the simulation analysis, the main frequency of the engine shellradiation noise is between600Hz to1200Hz and the main noise source is inthe convex department of the engine structure.The pseudo density chart which is built according to the shellstructural characteristics and noise shell analysis results and combined withHyperMesh10.0\OptiStruct optimize engine structure topologically. Thischart has an optimization design of increasing the thickness and addingstrengthen tendons on the structure. And then having a noise comparisonbetween the model before and after the optimization design, the resultsshow that the optimized engine shell surface radiated noise is lowersignificantly. It is reduced by4dB.