• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.125-135
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• 2004

This paper describes the calculation technique for guided wave propagation with a semi-analytical finite element method (SAFEM) and shows some results of numerical calculation and guided wave simulation for plates, pipes and railway rails. The SAFEM calculation gives dispersion curves and wave structures for bar-like structures. Dispersion curve software for a pipe is introduced, and also dispersion corves for a rail are given and experimentally verified. The mode conversions in a plate with a defect and in a pipe with an elbow or a defect are shown as examples of our guided wave simulations.

• Journal of Korean Society of Water and Wastewater
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• v.10 no.3
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• pp.64-72
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• 1996

The one of the most important factors we shoud consider in designing the processes using porous media such as activated carbon adsorber is the prediction of the breakthrough curve. In this study, the breakthrough curve of BAC process for the treatment of refractory pollutants was evaluated by simplified engineering analysis. Through the experiments, the slope of the breakthrough curve can be determined by retardation factor, R and apparent dispersion coefficient, $D_{app}$ which is determined by hydrodynamic dispersion, mass transfer effects and isotherm. Estimated concentration of effluent was agreed with the experimental values. Also, it is possible to use this method for predicting the breakthrough curve of the pollutants removal and tranport of pollutants in porous media.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.1
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• pp.133-140
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• 2001

Recently, to assure the integrity of a structural components such as piping pressure vessels and thinning structure, Lamb wave inspection technique has been used in material evaluation. It is very important to select the optimal Lamb wave mode and to analyze the signal accurately because of its unique dispersion properties grnerating several modes within the speci-men. It this study, the feasibility of material evaluation applications using wavelet analysis of Lamb wave has been veir-fied experimentally. These results show as follows; 1)dispersion characteristic of each mode in dispersion curve is demon-strated that A0 mode propagating material surface is useful mode having the lest energy loss and not sensitive to surface condition. 2) it can be detected even the micro defect ($1\times2mm$) fabricated in ultrasonic probe flaw distance (290mm) to axis direction. 3) the wavelet transform which is called "time-frequency analysis" shows the Lamb wave propagation due to the change of materials characterization can be evaluated at each frequency and experimental group velocity of Lamb wave agrees quite well with that of simulated dispersion curve.ion curve.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.15-24
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• 2006

The evaluation of shear modulus is very important in various fields of civil engineering. Non-destructive seismic methods can be used to determine shear wave velocity ($V_s$) profile. Non-destructive seismic methods geneally consist of three steps: field testing, evaluation of dispersion curve, and determination of Vs profile by inversion process. Non-destructive seismic methods can be divided into two categories according to the number of receivers used for data reduction: two-channel tests and multi-channel tests. Two channel tests use apparent velocity dispersion curve and multi-channel tests use mode dispersion curves. Multi-channel tests using mode dispersion curve can reduce calculation time to determine soil profile and uncertainties in inversion process. So far, only multi-channel tests can determine mode dispersion curves but multi-channel test needs many receivers to determine reasonable mode dispersion curves. In this paper, HWAW (Harmonic Wavelet Analysis of Wave) method is applied to determine mode dispersion curves. HWAW method uses short test setup which consists of two receivers with a spacing of 1 to 3 m. Through numerical simulations and field application, it is shown that HWAW can determine resonable mode disperson curves.

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.154-156
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• 2001

• Journal of Radiation Protection and Research
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• v.38 no.2
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• pp.60-67
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• 2013

A diffusion coefficient is an important parameter in the prediction of atmospheric dispersion using a Gaussian plume model, and its modelling approach varies. In this study, dispersion coefficients recommended by the U. S. Nuclear Regulatory Commission's (U. S. NRC's) regulatory guide and the Canadian Nuclear Safety Commission's (CNSC's) regulatory guide, and used in probabilistic accident consequence analysis codes MACCS and MACCS2 have been investigated. Based on the atmospheric dispersion model for a hypothetical accidental release recommended by the U. S. NRC, its influence to atmospheric dispersion factor was discussed. It was found that diffusion coefficients are basically predicted from a Pasquill- Gifford curve, but various curve fitting equations are recommended or used. A lateral dispersion coefficient is corrected with consideration for the additional spread due to plume meandering in all models, however its modelling approach showed a distinctive difference. Moreover, a vertical dispersion coefficient is corrected with consideration for the additional plume spread due to surface roughness in all models, except for the U. S. NRC's recommendation. For a specified surface roughness, the atmospheric dispersion factors showed differences up to approximately 4 times depending on the modelling approach of a dispersion coefficient. For the same model, the atmospheric dispersion factors showed differences by 2 to 3 times depending on surface roughness.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.194-198
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• 2008

Several methods for improving dispersion of carbon nanotubes (CNTs) have been investigated. CNTs modified by acids and hydrogen peroxide ($H_2O_2$) showed improved dispersion. From SEM micrographs and photos of dispersion, CNTs modified with nitric acid and $H_2O_2$, showed no agglomeration in solution even standing for 4 months, which means successfully improved dispersion property. TEM micrographs of surface modified single CNT treated with 69% $HNO_3$ in boiling acid solution as the optimum method were obtained. For confirmation of CNTs' application to EDLC electrode materials, characteristics of EDLC have been analyzed by cyclic voltammetry curve, specific capacitance of unit cell, electrode discharge curves and AC impedance curve. From the results, it could be confirmed that electrochemical properties of CNTs were enhanced after surface modification with 69% $HNO_3$ acid treatment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.2
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• pp.72-79
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• 2021

The present paper aims to set forth a two-dimensional theory for the dynamics of plates that is valid over a large range of excitation. To construct a dynamic plate theory within the long-wavelength approximation, two dimensional-reduction procedures must be used for analyzing the low- and high-frequency behaviors under the dynamic variational-asymptotic method. Moreover, a separate and logically independent step for the short-wavelength regime is introduced into the present approach to avoid violation of the positive definiteness of the derived energy functional and to facilitate qualitative description of the three-dimensional dispersion curve in the short-wavelength regime. Two examples are presented to demonstrate the capabilities and accuracy of all of the formulas derived herein by using various dispersion curves through comparison with the three-dimensional finite element method.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.230-241
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• 2008

Characteristics of transfer responses for arrays like triangle, hexagon and semicircle were investigated. To characterize the site near Izmit city with ambient noise measurement, dispersion curves of surface waves were derived with using array technique like F-K, High resolution F-K, MSPAC and H/V ratio was calculated. Also, MASW was surveyed to get the high frequency part of dispersion curves. The transition from fundamental mode to first high mode of surface waves for dispersion curve was observed. Dispersion curve of fundamental mode of ambient noise and first higher mode of MASW was used in inversion to get S-wave velocity structure of subsurface. None-unique problem of results of surface wave inversion was solved with comparison of result of refraction tomography performed with first arrivals of MASW data.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1997.05a
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• pp.79-82
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• 1997

토양내에서 오염유기물질이 불포화토양내에 유입될 때의 dispersion coefficient를 adsorption과 desorption과정에 대해 알아보았다. apparent dispersion coefficient를 측정하기 위해 일상적인 상대습도(46%)조건에서 parametric analysis를 행하였다. 실험에 사용된 토양은 fine sand와 silt-clay혼합시료였고, 흐름방향은 상향과 하향으로 하였다. 그리고, Freon gas를adsorbing solute로 사용하였다. 오염물질로는 DCM, TCE, DCB를 사용하였다. 분석을 위해서 linear와 probability scale의 breakthrough curve를 사용하였다. 공기에서의 diffusion coefficient의 예측을 위하여 Graham's law를 계산에 사용하였고, DCM diffusion coefficient는 0.098$\textrm{cm}^2$/s로 계산되었다. 연구결과, adsorption과 desorption의 속도는 차이가 있는 것으로 나타났으며, diffusion이 flow regime을 좌우하는 것으로 나타났다. 그리고, desorption에서의 D$^{a}$ D$^{o}$ 는 1보다 클수도 있다. 또한, dispersion은 silt-clay혼합시료에서의 속도와 함께 증가한다. dispersion은 Freon의 sorption방향에 크게 의존한다.