• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.12
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• pp.1683-1689
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• 2014

In this paper, we propose an image processing based time-frequency domain reflectometry(TFDR) in order to estimate the fault location of a cable. The Wigner-Ville distribution is used for analysis in both the time domain and the frequency domain when the conventional TFDR estimates the fault location in a cable. However, the Winger-Ville distribution is a bi-linear function, and hence the cross-term is occurred. The conventional TFDR cannot estimate the accurate fault location due to the cross-term in case the fault location is close to the position where the reference signal is applied to the cable. The proposed method can reduce the cross-term effectively using binarization and morphological image processing, and can estimate the fault location more accurately using the template matching based cross correlation compared to the conventional TFDR. To prove the performance of the proposed method, the actual experiments are carried out in some cases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1075-1075
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• 2006

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.549-557
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• 2019

The acoustical scattering characteristics of a target are influenced by the material properties and structural characteristics of the target, which are critical information for acoustic detection and identification of underwater target. In particular, for thin elastic target, unique scattered signals are generated around the target by the Lamb wave. In this paper, the results of scattered signal measurement of aluminum spherical shell in the water tank using the stepped frequency sweep sine signal are presented. In particular, the scattering of the water-filled aluminum spherical shell is compared with that of the air-filled one both theoretically and experimentally. The difference of the scattered signals are analyzed using the pseudo Wigner-Ville distribution in terms of average frequency, frequency distribution, and energy of the scattered signal. The result shows that all observed parameters increased when the aluminum sphere was water-filled, and it is well matched to the theoretical expectation.

• The Journal of the Acoustical Society of Korea
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• v.26 no.3
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• pp.123-128
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• 2007

This Paper Presents new transient signal classification algorithms for underwater transient signals. In general. the ambient noise has small spectral deviation and energy variation. while a transient signal has large fluctuation. Hence to detect the transient signal, we use the spectral deviation and power variation. To classify the detected transient signal. the feature Parameters are obtained by using the Wigner-Ville distribution based eigenvalue decomposition. The correlation is then calculated between the feature vector of the detected signal and all the feature vectors of the reference templates frame-by-frame basis, and the detected transient signal is classified by the frame mapping rate among the class database.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2011.10a
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• pp.439-440
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• 2011

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.4
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• pp.270-276
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• 1999

Fourier transform has been one of the most commonly used tools in study of frequency characteristics of signal. However, based on the Fourier transform. it is hard to tell whether a signal's frequency contents evolve in time or not. Recently, to overcome Fourier transform fault. not to represent non-stationary signal, time-frequency analysis methods are developed and those can represent informations of signal's time and frequency at the same time. In this study we analysed ultrasonic signal for degraded SUS 316 with time-frequency analysis method. In particular the methods such as short time Fourier(STFT) and Wigner-Ville distribution(WVD) were used to extract frequency contents and characteristics from ultrasonic signals.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1158-1164
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• 2006

For the description of the elastic properties of linear objects a convenient parameter is the ratio of the stress to the strain, a parameter called the Young's modulus of the material. Young's modulus can be used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material. Conventional method for estimating Young's modulus measured the ratio of stress to corresponding strain below the proportional limit of a material using a tensile testing machine. But the method needs precision specimens and expensive equipment. In this paper, we proposed method for estimating Young's modulus using accelerometer. The basic idea comes from that the wave velocity is different as the Young's modulus. To obtain Young's modulus, a group velocity is obtained. It is difficult to measure group velocity. This is because plate medium has a dispersive characteristics which has different wave speed as frequency. In this paper, we used Wigner-Ville distribution to measure group velocity. To verify the proposed method, steel and acryl plate experiments have been performed. Experimental results show that the proposed method is powerful for estimating Young's modulus.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1027-1032
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• 2007

For the description of the elastic properties of linear objects a convenient parameter is the ratio of the stress to the strain, a parameter called the Young's modulus of the material. Young's modulus can be used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material. Conventional method for estimating Young's modulus measured the ratio of stress to corresponding strain below the proportional limit of a material using a tensile testing machine. But the method needs precision specimens and expensive equipment. In this paper, we proposed method for estimating Young's modulus using accelerometer. The basic idea comes from that the wave velocity is different as the Young's modulus. To obtain Young's modulus, a group velocity is obtained. It is difficult to measure group velocity. This is because plate medium has a dispersive characteristics which has different wave speed as frequency. In this paper, we used Wigner-Ville distribution to measure group velocity. To verify the proposed method, steel and acryl plate experiments have been performed. Experimental results show that the proposed method is powerful for estimating Young's modulus.

• Nuclear Engineering and Technology
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• v.41 no.3
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• pp.327-334
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• 2009

Elastic wave is one of the most useful tools for non-destructive tests in nuclear power plants. Since the elastic properties are indispensable for analyzing the behaviors of elastic waves, they should be predetermined within an acceptable accuracy. Nuclear power plants are exposed to harsh environmental conditions and hence the structures are degraded. It means that the Young's modulus becomes unreliable and in-situ measurement of Young's modulus is required from an engineering point of view. Young's modulus is estimated from the group velocity of propagating waves. Because the flexural wave of a plate is inherently dispersive, the group velocity is not clearly evaluated in temporal signal analysis. In order to overcome such ambiguity in estimation of group velocity, Wigner-Ville distribution as the time-frequency analysis technique was proposed and utilized. To verify the proposed method, experiments for steel and acryl plates were performed with accelerometers. The results show good estimation of the Young's modulus of two plates.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.255-262
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• 2006

Frequency spectrum using the conventional Fourier analysis gives adequate information about the dynamic characteristics of the slider air bearing for the linear and stationary cases. The intermittent contacts for the extremely low flying height, however, generate nonlinear and nonstationary vibration at the instant of contact. Nonlinear dynamic model should be developed to simulate the impulse response of the air bearing during slider-disk contact. Time-frequency analysis is widely used to investigate the nonstationary signal. Several time-frequency analysis methods are employed and compared for the slider vibration signal caused by the impact against an artificially induced scratch on the disk. The representative Wigner-Ville distribution leads to the severe interference problem by cross terms even though it gives good resolution both in time and frequency. The smoothing process improves the interference problem at the expense of resolution. In order to get the results with good resolution and little interference, the reassignment method is proposed. Among others the reassigned Gabor spectrogram shows the best resolution and readability with negligible interference.