Application Of Partial Coherence Analysis Based On Energy Distribution For Low Frequency Noise Reduction Of Coach

The development of automotive technology,to the present,already has a history of more than 100 years.With continuous improvement of usability and safety,the gap between the various car brands is also decreasing.Meanwhile,people's requirement for the overall performance of automotive have become increasingly high,and more attention has been paid to the comfort performance of automotive.The interior noise has become one of the important indicators to evaluate the riding comfort.Excessive interior noise of vehicle will result in fatigue and irritable of passenger and then influences the driving safety.Therefore,reducing interior noise of coach effectively has important significance.This dissertation takes a coach as research object,and the interior noise is studied by a method of experiment integrated with numerical simulation.Firstly,the acoustic characteristics of coach interior noise are tested,and it is found that the noise is concentrated in low frequency band by spectrum analysis and wavelet packet analysis.The interior low-frequency noise is structure-borne noise and it has been attracted the focuses of automotive interior noise research.It always needs to identify the vibrating structures that have greater impact on interior noise.Contribution of vibration to the noise of field points fails to completely represent the contribution to the whole interior acoustic field.For the interior acoustic field with multiple frequency peaks and multiple field points,the energy weighting coefficients are introduced into the partial coherence analysis method according to the energy distribution of the measured point sound pressure signal.Then the "total coherence coefficient "and"coherence coefficient sum",as two new parameters are introduced to evaluate the effect of vibration of body panels on the interior noise.The panels having greater impact on interior noise were identified by the coherence analysis of panel vibration and noise signal.Secondly,the BIW(Body In White)finite model and interior acoustic cavity finite model are built to predict the interior low-frequency noise and modal participation factor.The modes having greater contribution to sound pressure frequency response are identified by modal participation factor analysis.Based on the results of partial coherence analysis,the specific parts are pinpointed to suppress the vibration.Finally,constrained damping material are pasted on those panels.The simulation results show that the sound pressure signals of each field point are decreased,and the amplitude of peak frequencies are decreased obviously.In order to validate the effect of this analysis and improved method,real vehicle noise test is conducted after pasting damping material.The results show that interior noise is improved obviously,and the sound pressure level of field points decreased by 1.8dB?3.2dB.According to the results of simulation and experiment,the research method in this dissertation can provide reference for effectively reducing the low frequency noise inside coach.