Identification of the Impact Location in a Gas Duct System Based on Acoustic Wave Theory and the Time Frequency

This paper presents a new method for detecting the impact location in a buried gas duct. Gas leakage is often caused by the mechanical impact forces of construction equipment. In order to prevent gas leakage due to an impact force, it is necessary to detect the impact location at an early stage. For the detection of the impact location in a pipeline system, the correlation method has been used as the conventional method. For the application of the correlation method, the diameter of a duct should be small so that the acoustic wave inside the duct can propagate with non-dispersive characteristics, in the form of, for example, a plane wave. However, when the diameter of the duct is large, the acoustic waves inside the duct propagate with dispersive characteristics owing to the reflection of the acoustic wave off of the wall of the duct. This dispersive characteristic is related to the acoustic modes inside a duct. Therefore, the correlation method does not work correctly for the detection of the impact location. This paper proposes new methods of accurately measuring the arrival time delay between two sensors attached to duct line system. This method is based on the time-frequency analyses of the short time Fourier transform (STFT) and continuous wavelet transform (CWT). These methods can discriminate direct waves (non-dispersive waves) and reflective waves (dispersive waves) from the measured wave signals through the time-frequency analysis. The direct wave or the reflective wave is used to estimate the arrival time delay. This delay is used for the identification of the impact location. This systematic method can predict the impact location due to the impact forces of construction equipment with more accuracy than the correlation method.