Papers by Author: Jang Moo Lee

Abstract: The aim of this paper is to propose a robust method for extracting damping ratios of a railway contact wire using a continuous wavelet transform (CWT). It is hard to measure the damping ratios of the contact wire because the contact wire has close natural modes in a low frequency range and the dynamic signals of the contact wire gathered in the field are easily corrupted by extraneous noises. The proper choice of the wavelet parameters to decouple the close modes is required in order to obtain accurate damping ratios for the railway contact wire. In this paper, we investigated CWT error terms and derived a relation between a frequency resolution and complex Morlet wavelet parameters. In order to show the accuracy of the proposed method, we extracted damping ratios for the simulated pure and noisy signals which have close natural modes. According to the results, the proposed method can provide the damping ratios well agreed with true ones even for the noisy data. Finally, we applied the proposed method to the contact wire of a conventional railway line in Korea in order to verify the applicability in the field. The damping ratios extracted from the real data were in the range from 0.01 to 0.04.

Abstract: The railway contact wire, which supplies electric railways with electric power, plays an important role in determining the maximum railway velocity. In general, the maximum allowable velocity of an electric railway is less than seventy percent of the wave propagation velocity of the contact wire. Because the contact wire is more a beam model with dispersive wave characteristics than a string model, the wave propagation velocity depends on the frequency. For this reason, there have been only few studies on the wave propagation of the contact wire. In this paper, we proposed two useful methods for estimating the wave propagation velocity of the railway contact wire by using the Gabor wavelet transform on the experimental signals. In the first method, the ridges of wavelet transform, which contain the essential information about dispersive characteristics, are used. Specifically, the wave propagation velocity of the contact wire can be extracted from the time difference of the wavelet ridges of the measured signals. In the second method, the cross-correlation analysis of each wavelet transform is used to extract the wave propagation. The selection of the optimal Gabor shaping factor for the best time-frequency localization by using the Shannon entropy cost function is also discussed.