• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.32-37
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• 2002

The presence of hydrogen in industrial plants is a source of damage. Hydrogen attack is one such form of degradation and often causing large tube ruptures that necessitate an immediate shutdown. Hydrogen attack may reduce the fracture toughness as well as the strength of steels. This reduction is caused partially by the presence of cavities and microcracks at the grain boundaries. In the past several techniques have been used with limited results. This paper describes the application of an ultrasonic velocity and attenuation in hydrogen damage. Ultrasonic tests showed a decrease in wave velocity and an increase in attenuation. Such results demonstrate the potential for ultrasonic nondestructive testing to quantify damage. Based on this study, reliable recommendation is suggested to detect hydrogen attack.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3558-3565
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• 2024

The linear attenuation coefficients (LAC) of four soils (Black cotton (S1), Sandy (S2), Clay (S3), and Sandy (S4)) samples were measured at photon energies released from radioisotopes Co⁵⁷ (122 keV), Ba¹³³ (356 keV), ²²Na (511 and 1275 keV), Cs¹³⁷ (662 keV), Mn⁵⁴ (840 keV), and Co⁶⁰ (1330 keV) using a gamma spectrometer includes a NaI (Tl) scintillation detector. The experimental measurements were confirmed utilizing the Monte Carlo N-particle transport code. The linear attenuation coefficient values enhanced from 0.256 cm^-1 to 0.296 cm^-1 (at E_γ of 122 keV), from 0.126 cm^-1 to 0.142 cm^-1 (at E_γ of 662 keV), and from 0.0938 cm^-1 to 0.105 cm^-1 (at E_γ of 1275 keV), raising the (Fe + Mn) concentration from 0.912 wt% to 11.214 wt%, as well as raising the soil samples density from 1.62 g/cm³ to 1.79 g/cm³. The study also shows an enhancement in the half value thickness, transmission factor, radiation protection efficiency and lead's equivalent thickness due to the enrichment of Fe + Mn concentrations within the studied soils. The results show that the Black cotton soil exhibits better shielding properties for γ-ray than the other soils.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.417-423
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• 2000

A broadband antenna available in the range of 30MHz for electromagnetic interference (EMI) test is proposed in this paper, This antenna is configurated in a disk-loaded cylindrical dipole (DLCD) connected to an 180。 hybrid balun consisting of two coaxial feeders. The performance of EMI antenna is characterized with its accurate antenna factor. The antenna factor for this antenna is obtained by using the method of moments and the calculated results are compared with the measured ones. Normalized site attenuation (NSA) is also measured by using this antenna. The results present that the propose antenna could be used for a reference antenna having measurement reproducibility and represented by a theoretically accurate analysing model in EMI measurement.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.10
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• pp.1774-1779
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• 2016

This paper proposes a portable cable fault detection system with automatic fault distinction and distance measurement using time-frequency correlation and reference signal elimination method and automatic fault classification algorithm in order to have more accurate fault determination and location detection than conventional time domain refelectometry (TDR) system despite increased signal attenuation due to the long distance to cable fault location. The performance of the developed system method was validated via an experiment in the test field constructed for the standardized performance test of power cable fault location equipments. The performance evaluation showed that accuracy of the developed system is less than 1.34%. Also, an error of automatic fault type and location by detection of phase and peak value through elimination of the reference signal and normalization of correlation coefficient and automatic fault classification algorithm not occurred.

• Journal of information and communication convergence engineering
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• v.14 no.3
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• pp.153-162
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• 2016

Microwave and millimeter waves are considered suitable frequency ranges for diverse applications. The prediction of rain attenuation required the 1-min rainfall rate distribution, particularly for data obtained locally from experimental measurement campaigns over a given location. Rainfall rate data acquired from Korea Meteorological Administration (KMA) for nine major sites are analyzed to investigate the statistical stability of the cumulative distribution of rainfall rate, as obtained from a 10-year measurement. In this study, we use the following rain rate conversion techniques: Segal, Burgueno et al., Chebil and Rahman, exponential, and proposed global coefficient methods. The performance of the proposed technique is tested against that of the existing rain rate conversion techniques. The nine sites considered for the average 1-min rain rate derivation are Gwangju, Daegu, Daejeon, Busan, Seogwipo, Seoul, Ulsan, Incheon, and Chuncheon. In this paper, we propose a conversion technique for a suitable estimation of the 1-min rainfall rate distribution.

• ETRI Journal
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• v.39 no.1
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• pp.76-86
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• 2017

In this study, we propose an automatic contrast enhancement method based on transfer function modification (TFM) by histogram equalization. Previous histogram-based global contrast enhancement techniques employ histogram modification, whereas we propose a direct TFM technique that considers the mean brightness of an image during contrast enhancement. The mean point shifting method using a transfer function is proposed to preserve the mean brightness of an image. In addition, the linearization of transfer function technique, which has a histogram flattening effect, is designed to reduce visual artifacts. An attenuation factor is automatically determined using the maximum value of the probability density function in an image to control its rate of contrast. A new quantitative measurement method called sparsity of a histogram is proposed to obtain a better objective comparison relative to previous global contrast enhancement methods. According to our experimental results, we demonstrated the performance of our proposed method based on generalized measures and the newly proposed measurement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.5
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• pp.1280-1290
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• 1995

In order to investigate the compression wave propagating in a high-speed railway tunnel, a numerical calculation was applied to the wave phenomenon occurring in a model tunnel. Unsteady, one-dimensional inviscid or viscous flows were solved by an explicit TVD scheme, and the calculated flows were compared with the results of measurement in real tunnels. Tunnel noises caused by emission of the compression wave were characterized in terms of excess pressure of compression wave, pressure gradient in the wave front and width of the compression wave. Calculated attenuation, pressure gradient and width of compression wave with the propagating distance agreed with the results of measurement in the real tunnels. The results also show that tunnel noises are proportional to the train velocity entering the tunnel.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.718-723
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• 2004

The insertion loss of a noise barrier comes from the effects of diffraction, transmission loss, absorption coefficient and attenuation by direct propagation. The noise level after the noise barrier, differs reatly from the diffraction on the upper part of the barrier. Maekawa, furze and Anderson presented a empirical formula for calculating the diffraction of a semi infinte screen shaped noise barrier. In this syudy, Noise reduction performance software was developed for the proper design and assessment of new plastic barrier . Predicted sound pressure level from using the software is compared with the site-measurement results to verify the noise reduction performance and feasibility of prediction software for insertion loss of noise barrier.

• Journal of the Korean Institute of Navigation
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• v.19 no.1
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• pp.9-16
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• 1995

We are confronted with the serious EMI(electromagnetic interference) problems in company with the development of electronic equipments. Accordingly it is also required to construct some anechoic chambers for EMI measurement. Furthermore it is very important to evaluate the chamber characteristics in advance of its construction. For that purpose we have analyzed the characteristics by computer simulation in base on the image method, and compared the results with the measured ones. In case of 3-meter method as a result, the curved line of height pattern of open site varies similarly as that of height pattern of anechoic chamber. When we measure the electromagnetic strength and can get the height pattern curves by frequencies, we utilized it effectively because we can protect instrumental errors in measurement. On the other hand, there is a little difference in site attenuation above 700MHz. When the ferrite grid was used however, the calculated values agree well with the measured values up to 1000MHz with the exception of 30-40 MHz range. The reason is that we don't consider the antenna coupling in the low frequencies of 30-100MHz range.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.2
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• pp.154-160
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• 1993

A mothod to decide the optimal frequency for the fracture velocity measurement by ultrasonic fractography is presented. A theoretical formula to decide the optimal frequency for ultrasonic fractography testing is made and it is compared with experimental value. According to the formula the optimal frequency is shown to be depending on the attenuation coefficient and size(width) of the specimen. In the case of PMA specimen with ligament 43mm the theoretical value for the optimal frequency is about 260 KHz and it is good agreement with experimental value.