Abstract Spatially dense vibration measurement can be obtained by use of a continuously scanning laser Doppler vibrometer (CSLDV) system that sweeps its laser spot along a scan path. For a linear, time-invariant, viscously damped structure undergoing free vibration, a type of vibration shapes called free response shapes was defined and obtained by the authors using a CSLDV system with the demodulation method. To date, application of free response shapes is limited to structural damage identification, and they cannot be directly used for model validation while mode shapes can be. This paper extends the concept of free response shapes by proposing a new modal parameter estimation (MPE) method using a CSLDV system to estimate modal parameters of the structure undergoing free vibration, including natural frequencies, modal damping ratios, and mode shapes; the MPE method is applicable to linear structures without repeated and closely spaced modes. Advantages of the proposed method are: (1) modal damping ratios and mode shapes can be accurately estimated from obtained free response shapes in the least-square sense, (2) the scanning frequency of the CSLDV system can be relatively low, and (3) estimated mode shapes can be used for structural damage identification as if they were measured by stepped scanning of a scanning laser Doppler vibrometer. A baseline-free method is applied to identify structural damage using mode shapes estimated by the proposed MPE method. The method does not require any baseline information of an undamaged structure, such as its complete geometry, material properties, boundary conditions, modal parameters, and operating deflection shapes. In the proposed MPE method, natural frequencies of the structure are identified from free response of certain fixed points on the structure; its modal damping ratios and mode shapes are simultaneously estimated using free response shapes measured by a CSLDV system. Both numerical and experimental investigations are conducted to study the MPE method and its application to baseline-free damage identification with mode shapes estimated by the MPE method.

中文翻译：

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使用连续扫描激光多普勒测振仪系统测量的自由响应进行模态参数估计，并应用于结构损伤识别

摘要 使用连续扫描激光多普勒测振仪 (CSLDV) 系统沿扫描路径扫描其激光光斑，可以获得空间密集振动测量。对于经历自由振动的线性、时不变、粘性阻尼结构，作者使用具有解调方法的 CSLDV 系统定义并获得了一种称为自由响应形状的振动形状。迄今为止，自由响应形状的应用仅限于结构损伤识别，它们不能直接用于模型验证，而模态形状可以。本文扩展了自由响应形状的概念，提出了一种新的模态参数估计 (MPE) 方法，使用 CSLDV 系统来估计承受自由振动的结构的模态参数，包括固有频率、模态阻尼比、和振型；MPE 方法适用于没有重复和紧密间隔模式的线性结构。所提出方法的优点是：（1）可以从最小二乘意义上的自由响应形状中准确估计模态阻尼比和模态振型，（2）CSLDV系统的扫描频率可以相对较低，以及（3 ) 估计的振型可用于结构损伤识别，就好像它们是通过扫描激光多普勒振动计的步进扫描测量的一样。一种无基线方法用于使用由所提出的 MPE 方法估计的模式形状来识别结构损坏。该方法不需要任何未损坏结构的基线信息，例如其完整的几何形状、材料特性、边界条件、模态参数和工作挠度形状。在提出的 MPE 方法中，结构的固有频率是从结构上某些固定点的自由响应中识别出来的；使用由 CSLDV 系统测量的自由响应形状同时估计其模态阻尼比和模态振型。进行了数值和实验研究以研究 MPE 方法及其在使用 MPE 方法估计的模态形状的无基线损伤识别中的应用。