基于小波变换分析箱梁振动噪声的时频特性

为探讨列车激励引起箱梁振动噪声的时频特性，以32 m混凝土简支箱梁为例，现场实测箱梁各板件的振动和近场噪声，并采用小波变换结合MLP （modified Littlewood-Paley）小波基的方法进行信号处理. 引入小波脊线和小波能量比两个指标对信号的时频特性进行定量分析，在此基础上，探讨了行车速度和行车方向的影响规律. 研究结果表明:相比Morlet小波和Mexihat小波，MLP小波更清晰地刻画箱梁振动噪声在时-频两域的局部集中特性；箱梁噪声比振动的频变程度要小，且前者的小波能量在频域上更为集中；翼板振动和腹板振动的频变特性分别对行车速度和行车方向敏感；45～60 Hz范围是箱梁噪声控制的关键频率范围. 

Time-Frequency Characteristics of Box-Girder Vibration and Noise Based on Wavelet Transform

In order to explore time-frequency characteristics of train-induced box-girder vibration and noise, a simply-supported concrete box-girder with a span of 32 m was selected as the case, the vibration and near-field noise of the box-girder slabs were measured, and the signals were processed by using wavelet transform with the modified Littlewood-Paley (MLP) wavelet basis. Two indexes of wavelet ridge curve and wavelet energy ratio were introduced to quantitatively analyze time-frequency characteristics. On this basis, how train speed and driving direction affect time-frequency characteristics were discussed. The results show that compared with the Morlet basis and the Mexihat basis, the MLP basis can better depict the localization of box-girder vibration and noise in both time and frequency domains. Box-girder noise has less variation in frequency than the vibration, and the former’s wavelet energy is more concentrated in frequency domain. The variation of flange vibration and web vibration in frequency domain are sensitive to train speed and driving direction, respectively. The frequency range of 45 to 60 Hz is vital for box-girder noise mitigation.