Identification Of The Main Noise Sources Sound Field Of Moving Vehicle

Pass-by noise is an important indicator of vehicle NVH property, and manycountries have formulated laws and regulations to improve the traffic noise pollution.To reduce vehicle noise and improve the pass-by noise, the identification of main noisesources of automobile is the most important step of noise control. Except commonanalysis methods such as isolation method, frequency analysis, sound pressure analysis,sound intensity analysis, and numerical simulation method, recently, transfer pathanalysis, acoustic holography and beam-forming method are used to idetify the thevehicle noise sources. But for the limit of these methods, it is difficult to decompose theexterior sound field detailedly. So, the research of the method for identifying anddecomposing of exterior sound field quickly and accurately when the vehicle is movinghave very practical significance.First, the mathematical descriptions are created for all kinds of the engineeringobjects in the identification of exterior sound field of automobile assembly, includingthe coordinate systems for the spatial postions, and their transformations. The soundfields are defined, such as the source field, the measurement field, the array field, theholography field and the reconstruction field, and their temporal and spatialrelationships are desribed.According to the researching of the operational transfer path analysis of pass-bynoise, the transmission of each impact source signal of the vehicle and response pointhas been analyzed, and the mathematical description of the transmission has been builtas well. Comparing of the transfer function of traditional transfer path analysis and thecorrelation coefficient of signal processing, the physical significance of operationaltransfer path analysi has been completed. The principal component analysis andnormalization preprocessing of signal matrix are used to calculate the transfer functionmatrix, which has improved the accuracy of the transfer function calculation andresponse signal fitting.The time domain transfer path analysis method is proposed, and the normalfrequency analysis method is instead of time domain signal analysis of the sameposition. The impulse response function of the system composed by vehicle, road and response point is used to instead of transfer function to calculate the systemcharacteristics to reduce the error of the Fourier Transform for the deficiency ofsampling number when the vehicle is moving. The calculation is simplified for thespatial characteristics of noise sources and the impulse response function.A transfer path acoustic holography analysis method is proposed to decompose andidentify each incoherent independent impact sources and the noise characteristics of theautomobile assemblies. Affter the time domain transfer path analysis, the responsesignals of the array microphones are decomposed into the noise components of theseindependent impact sources, and then the sound field on the surface of vehicle can bereconstructed by these signals and acoustic holography method.The simulation of multi-sound sources has proved the transfer path acousticholography analysis method can decompose the sound field and identify the position ofnoise sources. The result shows that, this method has more accuracy than traditionalacoustic holography method for the identification of main noise sources and minimumamplitude sources. The application of this method shows that it can identify the effect ofdifferent noise component for the pass-by noise more accuracyly, and decompose thesurface sound field of vehicle, which can be used to propose the noise control plan.