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9 April 2010 Fractal theory and wavelet packet transform based damage detection method for beam structures
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The presence of noise greatly affects the effectiveness and robustness of structural damage detection methods. In this study, a new damage detection method for beam structures is presented, utilizing time, frequency and space domain information effectively. Local free vibrations of both undamaged and damaged signals are firstly extracted utilizing the Natural Excitation Technique (NExT). Then the signals are decomposed into the low frequency region and high frequency region by the wavelet packet transform (WPT). The Higuchi's fractal dimension (HFD) is applied to measure the complexity of new local signals, which combine the low frequency component of undamaged signals and high frequency component of damaged signals. Damage can be localized by the peak value of Katz's fractal dimension (KFD) analyzing the spatial curve of the calculated HFD values along the structure. For validation, the numerical studies of a simple supported beam were conducted. The results demonstrate that the method is capable of localizing single and multiple damage of various severity accurately. Furthermore, it is found that the proposed damage index is directly connected to damage severity. And the results of tests under heavy noise reveal strong robustness of the proposed method.
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Yong Huang, Yongchao Yang, and Hui Li "Fractal theory and wavelet packet transform based damage detection method for beam structures", Proc. SPIE 7650, Health Monitoring of Structural and Biological Systems 2010, 76503I (9 April 2010);

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