MEASUREMENT OF A DAMPING RATIO USING WAVELETS

초록

We proposed a damping extraction method for a contact wire using a continuous wavelet transform(CWT). We used two kinds of complex Morlet wavelets as a wavelet function. In order to show that the proposed method is valid, we extracted damping ratios from the free response of the simulated system which have close natural modes in a low frequency range similar to the contact wire. According to the results, the error is less than 8% at the first natural frequency(1Hz). The errors become larger at higher natural modes. However, the estimated damping ratios at higher modes are still agreed with the true values within 20% errors. More errors at higher natural modes are mainly due to a poor frequency resolution of the wavelet function used. For a reliable extraction of the damping ratios, we presented how to adjust a frequency resolution of the complex Morlet wavelet and how to remove noises in the free response in this paper. Because the CWT can decouple close natural modes of the contact wire, we can conclude that damping ratios can be extracted from the free response of the contact wire using the proposed method.

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