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Location Template Matching(LTM) 방법에 사용되는 유사성 척도들의 비교 연구
신기홍(Kihong Shin) 한국소음진동공학회 2014 한국소음진동공학회 논문집 Vol.24 No.4
The location template matching(LTM) method is a technique of identifying an impact location on a structure, and requires a certain measure of similarity between two time signals. In general, the correlation coefficient is widely used as the measure of similarity, while the group delay based method is recently proposed to improve the accuracy of the impact localization. Another possible measure is the frequency response assurance criterion(FRAC), though this has not been applied yet. In this paper, these three different measures of similarity are examined comparatively by using experimental data in order to understand the properties of these measures of similarity. The comparative study shows that the correlation coefficient and the FRAC give almost the same information while the group delay based method gives the shape oriented information that is best suitable for the location template matching method.
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Location Template Matching(LTM) 방법을 적용함에 있어서 진동 모드 수의 영향
신기홍(Kihong Shin) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.2
The location template matching (LTM) method is a technique of identifying an impact location on a structure, and is often applied to structural health monitoring and large scale human-computer interface (HCI) systems. The LTM method utilizes a certain measure of similarity between two time signals. The correlation coefficient is most widely used for this purpose, and the group delay based method is recently proposed to improve the accuracy of finding the best matching pair of signals. In practice, one of key essential consideration for implementing the LTM method is to guarantee that a sufficient number of vibration modes must be contained in the measured signal, and yet the lower sampling rate is needed for a real-time implementation. In this paper, the properties of correlation coefficient and group delay with respect to the number of vibration modes are investigated. A few important results are obtained through extensive computer simulations and experiments. If the number of vibration modes contained in the measured signal is more than four it is sufficient for the correlation based LTM method, while the group delay based LTM method requires smaller number of vibration modes.
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진동신호를 이용한 회전기계의 상태감시를 위한 손상지수 개발 및 대형 원심압축기에 적용 사례
신기홍(Kihong Shin) 한국소음진동공학회 2017 한국소음진동공학회 논문집 Vol.27 No.7
Many machinery diagnosis methods and strategies utilizing measured vibration signals have been developed greatly over the last a few decades and used as a key element in the area of condition-based maintenance (CBM). Most of these sophisticated diagnosis methods focus on appropriate feature extraction from the measured signals in the time, frequency, and time-frequency domains, and generally require engineers to have specific knowledge of the method. However, it is often the case that field engineers are not well trained to apply these methods appropriately. Instead, they often want to know whether a machine under observation needs a further special inspection or not. In this paper, a few damage indexes are suggested for field engineers to determine easily whether the machinery under evaluation needs a further detailed examination. The proposed indexes are easy to interpret without requiring special knowledge. An example of using these indexes is demonstrated by applying to a large centrifugal compressor.
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진동신호를 이용한 회전기계의 상태감시를 위한 비정상 상태 지수 개발 및 대형 원심압축기에 적용 사례
신기홍(Kihong Shin) 한국소음진동공학회 2024 한국소음진동공학회 논문집 Vol.34 No.5
Statistical measures, such as standard deviation(or RMS), skewness, kurtosis, and spectral power of a measured vibration signal, are often used as key features when implementing a condition-based maintenance(CBM) system, particularly for rotating machinery. Typically, the CBM system monitors these statistical values and compares them with the values from an initial healthy state. However, it is often the case that the initial reference vibration signals are not available, making the implementation of the CBM system more challenging. In this study, as an alternative method to overcome this situation, non-stationary condition indexes are developed by capturing the non-stationary characteristics of measured vibration signals. The suggested non-stationary condition indexes are based on time-varying statistical measures and are applied to the same centrifugal compressor as in the previously published paper. The results are consistent with the previous findings, showing that the proposed non-stationary condition indexes may be useful alternative criteria, especially when the initial reference vibration signals are not available.
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외팔 보를 이용한 Location Template Matching 방법을 적용함에 있어서 격자간격의 영향 분석
신기홍(Kihong Shin) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.5
Measuring similarity between two signals is a key element of the location template matching (LTM) method which is one of impact source localization technique. As a measure of similarity, the correlation coefficient is most widely used, and the group delay based method is recently proposed to improve the accuracy of finding the impact source. In practice, the LTM method assumes that the similarity between two signals decreases as the distance between two corresponding impact points increases, where the distance between two neighboring impact points defines the grid spacing. In this paper, it is shown that this assumption is not always true but the correlation coefficients fluctuate forming a main robe and many side robes as the distance between two neighboring impact points increases. On the other hand, the standard deviation of group delay sharply increases with a small increase of the grid spacing. These are demonstrated by using a simple cantilever beam. Based on these findings, an optimal way of implementing the LTM method may be suggested by combining the correlation coefficient and the group delay based approaches.
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