惟输出小波基结构模态识别方法及其时频解析度研究

Output-only wavelet based structural modal identification and its time frequency resolution analysis

基于相关响应估计的连续小波变换分析方法可以从结构环境随机振动响应中识别出结构的模态参数,其中小波时频分析窗的设置对识别的准确性起着至关重要的作用。为此,展开这方面的研究,详细讨论了影响小波时频分析解析度的参数及时频分析窗的设置方法。对于频域解析度,通过调节母小波函数中心频率来满足对结构模态进行分离的要求。对于时域解析度导致的边界效应问题,通过在相关响应估计过程中对相关响应进行负延拓来解决此问题。采用一单塔双索面斜拉桥数值算例来验证方法的准确性并讨论了参数设置细节。数值算例分析的结果表明通过合理设置小波母函数中心分析频率及相关响应的延拓长度,可以很好地解决时频解析度相关问题,从而准确地从结构随机振动响应信号中识别出结构模态参数。

The time and frequency resolution of a covariance-driven wavelet analysis technique for identifying the modal parameters of linear systems from random vibration response measurements was discussed.The technique starts with the calculation of structural covariance responses from random vibration response of the system.The covariance was then converted into time-frequency domain using a continuous Morlet wavelet transform.The phase angles and the magnitudes of the covariance wavelet coefficients along the ridges were used to estimate structural modal parameters.To set an enough frequency resolution for modal separation,the central frequency of the mother wavelet function was proposed to be adjustable.To deal with the end effect of wavelet analysis,the negative covariance response was estimated as end padding.The numerical study on a single-pylon double-cable-plane cable-supported bridge verifies that the time-frequency resolution of the wavelet analysis can be fixed by setting a reasonable central frequency of the analyzing mother wavelets and the proposed negative covariance estimation technique is of good capability to eliminate the end effect of the wavelet analysis.