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A method for an accurate estimation of natural frequencies using swept-sine acoustic excitation

机译：一种使用正弦扫频声激发准确估计固有频率的方法

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Early detection of cracks in engineering structures by vibration-based methods requires monitoring systems that can evaluate natural frequencies with high accuracy. This paper introduces a method for estimating the natural frequencies using features extracted from the vibrational response of structures excited to cross through the resonance. To this aim, an open-loop acoustic system able to ensure bidirectional excitation, in swept-sine or short-time mode, with controllable parameters was developed. Analyzing the structural response at the crossing area through the resonance, two particularities on which the method is based have been revealed. The first refers to the symmetry of the frequency shift at peak amplitude from the natural frequency, if positive and negative sweep rates are applied. Therefore, the natural frequency can be found as the average of the frequency values at the resonance. Also, the necessary time to achieve the peak amplitude after passing through the natural frequency is similar, irrespective to the sign of the sweep rate. This accomplishment allows finding the natural frequency from a graphical representation. Frequency estimation made for a test structure by employing the two procedures lead to convergent results. Comparing these results to those achieved by impulsive excitation, a better precision was remarked at the swept-sine excitation. With regard the simplicity, rapidity and stability of the method, the swept-sine excitation has been proved as the most effective. (C) 2018 Elsevier Ltd. All rights reserved.
机译：通过基于振动的方法及早发现工程结构中的裂缝，需要使用能够高精度评估自然频率的监控系统。本文介绍了一种方法，该方法使用从受激励穿过共振的结构的振动响应中提取的特征来估计固有频率。为此，开发了一种开环声学系统，该系统能够确保以正弦扫频或短时模式进行双向激励，并且参数可控。通过共振分析交叉区域的结构响应，揭示了该方法所基于的两个特殊性。第一个是指如果施加正扫描率和负扫描率，则峰值振幅与自然频率的频移对称性。因此，固有频率可以作为共振时的频率值的平均值。同样，不管扫描速率的符号如何，在通过固有频率之后达到峰值幅度所需的时间都是相似的。该成就允许从图形表示中找到固有频率。通过采用这两种过程对测试结构进行频率估算，可以得出收敛的结果。将这些结果与通过脉冲激励获得的结果进行比较，在正弦扫频激励下具有更好的精度。关于该方法的简单性，快速性和稳定性，已证明扫频正弦激励是最有效的。 （C）2018 Elsevier Ltd.保留所有权利。

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