Tracing the source of unsteady-state low-frequency noise based on wavelet coherence analysis

The original partial coherence analysis method can be used to analyze the contributions between different noise sources and field points under steady-state conditions. Nevertheless, coherence analysis cannot be used to deal with unsteady-state signals because the signals are time-varying. In this paper, the method of panel contribution under unsteady-state conditions based on wavelet coherence analysis is proposed to determine the largest noise contribution in the cab. First, the unsteady-state simulation signals are analyzed by wavelet coherence theory. This step not only verifies the effectiveness but also points out that wavelet coherence is more superior to crossed wavelet. Second, the measured unsteady-state signals of the eight measuring points are processed by time-frequency wavelet coherent analysis. According to the obtained two-dimensional time-frequency diagrams, the contribution of different panels to the noise of measuring field points in the continuous frequency range can be found out. Then, the total contribution coefficient sum of each panel in a certain frequency band is calculated. Finally, the above analysis results are used to determine the panels with the largest contribution to the cab noise. The corresponding noise reduction scheme is also proposed. The results show that the overall sound pressure level is obviously decreased after optimization. The noise in the cab is reduced by 4.5dBA similar to 7dBA. The effectiveness of this method has been further verified by the above results.