Operational modal analysis using lifted continuously scanning laser Doppler vibrometer measurements and its application to baseline-free structural damage identification
Operational modal analysis using lifted continuously scanning laser Doppler vibrometer measurements and its application to baseline-free structural damage identification
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DOI：
10.1177/1077546318821154
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发表时间：
2019-04-01
影响因子：
2.8
通讯作者：
Zhu, W. D.
中科院分区：
文献类型：
--
作者：
Xu, Y. F.;Chen, Da-Ming;Zhu, W. D.
连续扫描激光多普勒测振仪（CSLDV）系统能够通过使其激光光斑沿着在结构上指定的扫描路径扫描来高效地和空间密集地测量振动。本文提出了一种新的操作模态分析（OMA）方法的基础上的数据处理方法CSLDV测量的结构，称为提升法，在白噪声激励下，并适用于基线自由的方法来识别结构损伤使用估计的模态振型从OMA方法。提升方法能够将原始CSLDV测量值转换为各个虚拟测量点的测量值，就好像后者是通过使用普通扫描激光多普勒振动计以分步方式进行的一样。研究表明，在白噪声激励下，结构上两个虚拟测量点的CSLDV测量值之间的非负时延相关函数及其功率谱包含结构的模态参数，即固有频率、模态阻尼比和振型。可以通过使用标准OMA算法来估计模态参数。建议OMA方法的一个主要优点是，曲率模态形状与模态形状估计的方法可以反映局部异常所造成的小尺寸的结构损伤，而那些估计由其他现有的OMA方法，使用CSLDV测量不能。对OMA方法和无基线结构损伤识别方法进行了数值和实验研究。在实验研究中，研究了CSLDV系统的扫描频率对这两种方法的影响。它示出在数值和实验研究中，模态参数可以准确地估计由OMA方法和结构损伤，可以成功地识别在具有一贯的高值的曲率损伤指数的邻域。
A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with nonnegative time delays between lifted CSLDV measurements at two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, that is, natural frequencies, modal damping ratios, and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.