Abstract This paper reports the results of an analytical, experimental and a numerical study (proof of concept study) on a proposed method for extracting the pseudo-free-vibration response of a structure using ambient vibration, usually of a random nature, as a source of excitation to detect any change in the dynamic properties of a structure that may be caused by damage. The structural response contains not only a random component but also a component reflecting the dynamic properties of the structure, comparable to the free vibration for a given initial condition. Structural response to the arbitrary excitation is recorded by one or several accelerometers with a desired data-collection frequency and resolution. The free-vibration response of the structure is then extracted from this data by removing the random component of the response by the method proposed in the paper. The features of the free-vibration response of the structure extracted by a suitable method, namely FFT in this study, can be used for change detection. Possible change of the pattern of these features is dominantly linked to the change in dynamic properties of the system, caused by possible damage. To show the applicability of the concept, besides an analytical verification using Newmark’s linear acceleration method, two steel portal frames with different flexural stiffness were made in the steel workshop of the structural laboratory for an experimental study. These structures were also numerically modeled using a finite element software. A wireless accelerometer with a sampling frequency rate of 2046 Hz was affixed on the top of the physical structure, at the same location where the acceleration was recorded for the corresponding numerical model. The physical structure was excited manually by an arbitrary hit and the response of the structure to this excitation, in terms of the acceleration on the top of the structure, was recorded. The pseudo-free-vibration response was extracted and transferred into frequency domain using FFT. The frequency with the largest magnitude which is the fundamental frequency of the structure was traced. This was repeated for several independent excitations and the fundamental frequencies were observed to be the same, showing that the process can correctly identify the natural frequencies of the structure. Similarly, the numerical model was excited and for several base excitation cases, the fundamental frequencies were found to be the same. Considering the acceptable accuracy of the results from the two numerical models in simulating the response of their corresponding physical models, additional numerical models were analyzed to show the consistency and applicability of the proposed method for a range of flexural stiffness. The results confirm that the proposed method can precisely extract the pseudo-free-vibration response of the structures and detect the structural frequencies regardless of the excitation. The fundamental frequency is tied to the stiffness and a larger stiffness leads to a higher frequency, as expected, regardless of the simulated ambient excitation.

中文翻译：

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关于提出的基于环境振动的方法来提取伪自由振动响应的概念验证研究

摘要 本文报告了一种分析、实验和数值研究（概念验证研究）的结果，该方法使用环境振动（通常具有随机性质）作为源提取结构的伪自由振动响应。以检测可能由损坏引起的结构动态特性的任何变化。结构响应不仅包含随机分量，还包含反映结构动态特性的分量，与给定初始条件下的自由振动相当。对任意激励的结构响应由一个或多个具有所需数据收集频率和分辨率的加速度计记录。然后通过本文提出的方法去除响应的随机分量，从该数据中提取结构的自由振动响应。通过合适的方法（即本研究中的 FFT）提取的结构的自由振动响应特征可用于变化检测。这些特征的模式可能发生的变化主要与系统动态特性的变化有关，这种变化是由可能的损坏引起的。为了证明该概念的适用性，除了使用Newmark 的线性加速度法进行分析验证外，还在结构实验室的钢车间制作了两个具有不同抗弯刚度的钢门式框架进行实验研究。这些结构也使用有限元软件进行数值模拟。采样频率为 2046 Hz 的无线加速度计固定在物理结构的顶部，与相应数值模型记录加速度的位置相同。物理结构通过任意撞击手动激发，并记录结构对这种激发的响应，即结构顶部的加速度。使用 FFT 提取伪自由振动响应并将其传输到频域。跟踪具有最大幅度的频率，即结构的基频。这对几个独立的激励重复进行，观察到基本频率相同，表明该过程可以正确识别结构的自然频率。相似地，数值模型被激发，对于几个基本激发情况，发现基本频率是相同的。考虑到两个数值模型结果在模拟其相应物理模型响应时的可接受精度，分析了额外的数值模型以表明所提出的方法在一定范围的弯曲刚度上的一致性和适用性。结果证实，所提出的方法可以精确地提取结构的伪自由振动响应，并在不受激励的情况下检测结构频率。基频与刚度有关，如预期的那样，更大的刚度会导致更高的频率，而与模拟的环境激励无关。考虑到两个数值模型结果在模拟其相应物理模型响应时的可接受精度，分析了额外的数值模型，以表明所提出的方法在一定范围的弯曲刚度下的一致性和适用性。结果证实，所提出的方法可以精确地提取结构的伪自由振动响应，并在不受激励的情况下检测结构频率。基频与刚度有关，如预期的那样，更大的刚度会导致更高的频率，而与模拟的环境激励无关。考虑到两个数值模型结果在模拟其相应物理模型响应时的可接受精度，分析了额外的数值模型以表明所提出的方法在一定范围的弯曲刚度上的一致性和适用性。结果证实，所提出的方法可以精确地提取结构的伪自由振动响应，并在不受激励的情况下检测结构频率。基频与刚度有关，如预期的那样，更大的刚度会导致更高的频率，而不管模拟的环境激励如何。对其他数值模型进行了分析，以表明所提出的方法在一定范围的弯曲刚度上的一致性和适用性。结果证实，所提出的方法可以精确地提取结构的伪自由振动响应，并在不受激励的情况下检测结构频率。基频与刚度有关，如预期的那样，更大的刚度会导致更高的频率，而与模拟的环境激励无关。对其他数值模型进行了分析，以表明所提出的方法在一定范围的弯曲刚度上的一致性和适用性。结果证实，所提出的方法可以精确地提取结构的伪自由振动响应，并在不受激励的情况下检测结构频率。基频与刚度有关，如预期的那样，更大的刚度会导致更高的频率，而与模拟的环境激励无关。