Research On Test Method Of Panel Contribution Based On Coherent Analysis

With the development of the peoples living level,people's requirements for the performance of vehicle NVH are getting higher and higher.The interior noi se is an important indicator for evaluating the performance of vehicle NVH.The noise inside the car is the more difficult part of acoustic sound insulation technology due to its mainly low frequency,and extremely strong penetration.The low frequency noise inside the car is mainly caused by the vibration of the panel radiating structural noise to the inner cavity of the car.In order to decrease the low-frequency noise inside the car,an effective method of panel contribution analysis is particularly impo rtant.This dissertation took a car as a research object,and the low frequency noise inside the car was studied by using the test method.A complete set of test method of panel contribution based on coherent analysis was established.Firstly,the road noise test was carried out on the car,and it was found that the noise inside the car is concentrated in low frequency band by wavelet packet analysis and spectrum analysis of the sound pressure signal in the vehicle.Secondly,the frequency response function curve of each vehicle panel was collected by hammering to determine the panel vibration measuring point.Then,through the vehicle road vibration and noise test,the vibration signal of the panel and the sound pressure signal inside the car were collecte d.The partial coherence analysis was used to determine the specific position of the vehicle panel that need vibration control.In order to further study the vibration source of the vehicle panel,this paper proposed a time-frequency analysis method based on Morlet wavelet coherence.The feasibility of this method was verified by the simulation analysis of the analog signal.Moreover,it was applied to the identification of the main excitation path of the vehicle,which determined the main excitation path c ausing the low frequency noise in the vehicle.This method not only reveals the correlation between two signals in the time-frequency domain,but also makes full use of the phase delay information between the two signals.It is so applicative widely that satisfy both steady state signals and non-steady state signals.Finally,the mass blocks were pasted on those panels and subsequently the road noise test was carried out.The results showed that the peak sound pressure level in the car decreases by 7dB(A)and the overall sound pressure level decreases by 1.4dB(A),which improve ride comfort of the car.Therefore,the test method of panel contribution based on coherent analysis can visually find the acoustic contribution of each individual vehicle panel to the noise in the human ear at continuous frequency.It solves the problem that the panel contribution based on simulation analysis can only focus on the contribution of a certain frequency point.Meanwhile,it also removes the mutual coupling between the panels,and improves the accuracy of the analysis results.This method for panel acoustic contribution has wider applicability.In summary,the complete set of test method of panel contribution based on coherent analysis and the time-frequency analysis based on Morlet wavelet coherence proposed in this paper have high engineering application value.I sincere hope to provide some guidance for the study of low frequency noise in the vehicle.