Prediction On Noise Radiated From Motorcycle Engine Shell

At present, experimental analysis and academic analysis become the two kinds of method to research on noise radiation from engine shell as the rapid development of the advanced test technology and computer technology. The first method can get the precise result, but the experimental equipment is expensive, besides, it always takes much time to solve the problem by experimental method when meetting the problem, so it can hardly satisfied the demand of the market. Research on noise radiation from engine shell by academic analysis,mainly based on Computer Aided Design and computer aided engineering (CAD/CAE), it can simulation by a computer and related CAD/CAE analytic software, although the academic result is not as precise as that gained by experiment, besides, it costs less time than experimental analysis from proposing the problem to solving the problem and carries on the simulation before getting the real object, so it can avoid physical damage, shorten the optimization time,and improve the work efficiency.The thesis takes an engine shell as a research object, through analysing it's vibration and noise characteristic by the method of academic analysis combined with the experimental analysis. The experimental analysis gives the academic analysis reasonable inspirator and verifies whether the academic method is correct, and the academic analysis gives the right direction to optimize the noise. Finally, acquaints the vibration and noise characteristic of the engine shell.In the experimental analysis aspect, through doing pass-by experiment to the motorcycle, finding the right side of the motorcycle exists resonant frequency around the 1kHz when the motorcycle is working. Through doing sound intensity experiment to the right side of the engine, finding the noise, which frequency around the 1kHz, mainly belongs to constructional noise is radiated from the engine shell. When integrative analyse these data, finding the noise radiation from engine shell leads to motorcycle produces large amount of noise to the exterior air. This result gives right direction to optimize the vibration and noise characteristic of the engine shell.Besides, doing mode experiment to the right side of the engine shell in order to futher analyse the vibration characteristic of the engine shell and give the experimental evidence when checking whether the finite element model is correct.In the academic analysis aspect, The vibration characteristic and radiated noise from the motorcycle engine shell are analysed with Finite Element Method/Boundary Element Method(FEM/BEM).The natural frequency is compared between FEM/BEM analysis and experimental analysis. The FEM/BEM results are agreed with the experimental results, which proves that the finite element modal is correct. Then the velocity response spectrum of the engine shell is acquired through the method of analysing the dynamic response under the vibration acceleration load. When comparing the academic data with the experimental data based on the same points on the shell,they are closed to each other. Finally, the structure's noise radiation is simulated by means of FEM/BEM in order to predict the noise radiation from the engine shell and gain the sound field characteristic outside the structure. The calculation data is compared with the experimental data in different frequency bands, analysing the reasons of the error, when compareing and analysing the academic data with experimental data, it reflects that FEM/BEM can predict the noise radiation from the engine shell effectively.After finding a reasonable way to compute the radiated noise, considering the characteristic of the engine shell and modifying the structure of the engine shell in a reasonable way, then predicting the noise radiation from the new engine shell by the same method, the academic data is proved by the experiment data again, besides, through modifying the structure of the engine shell in a reasonable way, reduces the noise radiation from the engine shell at 2.2dB(A), which proves that FEM/BEM can predict the noise radiation from the engine shell effectively again, and this method can easily optimize the noise radiation from engine shell.