Application of Wavelet Transforms to System Identification & Damage Detection in Frame Structure
Date Issued
2005
Date
2005
Author(s)
Ku, Chi-Jen
DOI
en-US
Abstract
Condition monitoring of dynamic system based on vibration signatures has relied on Fourier-based analysis as a mean of translating vibration signals in the time domain into the frequency domain. However Fourier analysis provided a representation of linear and stationary signal only. It is difficult to detect the signal pattern with abnormal and diluted information. The wavelet packet transform (WPT) is used as an alternative means of extracting time-frequency information from vibration signature. In this paper two research directions by using WPT to extract features from vibration signal are developed：one is the damage detection and the other is the modal parameters identification.
For damage detection the WPT feature extraction techniques are introduces to detect the occurrence of damage during the structural response time history. In the beginning based on feature vector of node energy of WP analysis, significant decomposed signals are developed. The amplitude of cross-wavelet coefficient power spectrum and the instantaneous phase features are generated. Damage detection can be identified from the maximum value of cross-wavelet coefficients and the phase lag. The holder exponents are also incorporated to detect the discontinuity of the signals. These methods can provide features of abnormal signal. To identify the modal parameters (natural frequencies and damping ratios) the wavelet packet sifting process is used to extract the dominant vibration signal of the system response. The sifting process can sift the decomposed signals under the conditions of a specified component energy and the entropy index. By converting the analytical signal using the Hilbert transform and its instantaneous frequency, the frequency-time domain of modal frequency and damping can be identified.
Application of the above-mentioned methods to data collected from a collapse test of a portal frame subject to seismic excitation on the shaking table is conducted. Through WPT on high frequency signal the occurrence of time where abnormal situation along the time response (such as time of negative stiffness in the restoring force, time of maximum yield force occurred during the excitation) can be detected. Dynamic characteristics of the portal frame are also identified from the WPT of low frequency signals.
Subjects
小波轉換之應用分析
結構物破壞情形的識別
系統特性的識別
Wavelet Transform
Damage Detection
System Identification
Type
thesis
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