• Journal of applied mathematics & informatics
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• 제35권3_4호
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• pp.241-260
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• 2017

An analysis is made to study the solute transport in a Casson fluid flow through an annulus in presence of oscillatory flow field and determine how this flow influence the solute dispersion along the annular region. Axial dispersion coefficient and the mean concentration expressions are calculated using the generalized dispersion model. Dispersion coefficient in oscillatory flow is found to be a function of frequency parameter, Schmidt number, and the pressure fluctuation component besides its dependency on yield stress of the fluid, annular gap and time in the case of steady flow. Due to the oscillatory nature of the flow, the dispersion coefficient changes cyclically and the amplitude and magnitude of the dispersion increases initially with time and reaches a non - transient state after a certain critical time. This critical value varies with frequency parameter and independent of the other parameters. It is found that the presence of inner cylinder and increase in the size of the inner cylinder inhibits the dispersion process. This model may be used in understanding the dispersion phenomenon in cardiovascular flows and in particular in catheterized arteries.

• 한국환경과학회지
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• 제3권1호
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• pp.11-16
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• 1994

Generally, it is difficult to predict water quality in a tidal river, because tidal flows make the transport phenomena more complicated. The purpose of this study is to clarify long-term mass transport in a tidal river through suggestion of simulation model. A simulation model based on a Lagrangian coordinate system, which has the advantage reducing numerical dispersion, was used to calculate changes in concentration of chlorides. Several field surveys were conducted to verify calculated results. Concludingly, long-term behavior of mas transport in a tidal river can be represented using the model.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 1997년도 총회 및 춘계 학술발표회 논문집
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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.

• 한국환경과학회지
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• 제11권9호
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• pp.907-914
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• 2002

Various Eulerian-Lagrangian models for the one-dimensional longitudinal dispersion equation in nonuniform flow were studied comparatively. In the models studied, the transport equation was decoupled into two component parts by the operator-splitting approach; one part is governing advection and the other is governing dispersion. The advection equation has been solved by using the method of characteristics following fluid particles along the characteristic line and the results were interpolated onto an Eulerian grid on which the dispersion equation was solved by Crank-Nicholson type finite difference method. In the solution of the advection equation, Lagrange fifth, cubic spline, Hermite third and fifth interpolating polynomials were tested by numerical experiment and theoretical error analysis. Among these, Hermite interpolating polynomials are generally superior to Lagrange and cubic spline interpolating polynomials in reducing both dissipation and dispersion errors.

• 융합정보논문지
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• 제10권12호
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• pp.236-244
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• 2020

본 연구에서는 하천실험센터에서 부유 물질 실험을 수행하여 부유 물질의 거동 및 확산을 관찰하고 이를 입자분산모형을 통하여 그 이동을 구현하고자 하였다. 규사를 물과 믹서기를 이용하여 혼합한 후 실규모 크기의 실험수로에 인위적으로 투입하고 레이저부유사측정기(LISST)를 이용하여 부유 물질의 농도를 측정하였다. 실험에서 드론 이미지 및 부유사 측정기 관측 데이터와 입자 분산 모형을 통해 부유 물질의 거동을 모의하여 비교한 결과, 비교적 실험 결과가 구현이 잘 된 것을 확인할 수 있었다. 이를 통하여 입자 분산 모형의 적용성은 물론, 높은 강우량으로 인한 유량 발생 시 부유 물질 예측 활용성을 기대할 수 있게 되었다.

• 한국군사과학기술학회지
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• 제26권1호
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• pp.102-112
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• 2023

This research mainly focuses on the transport and dispersion of chemical agent plume according to the Lagrangian Puff Model and Lagrangian Particle Model of NBC_RAMS(Nuclear, Biological, Chemical Reporting And Modeling S/W System). NBC_RAMS was developed with the purposes of estimating the fate of Chemical, Biological, and Radioactive(CBR) agent plumes and evaluating damages in the Republic of Korea. First, it calculates the local weather pattern, i.e. wind speed, wind direction, and temperature, by considering the effects of land uses and topography. The plume behaviors are calculated by adopting the Lagrangian Puff Model(LPFM) or Lagrangian Particle Model(LPTM). In this research, we assumed a virtual chemical agent exposure event in a stable atmospheric condition during the summer season. The plume behaviors were estimated by both LPFM and LPTM on the used area(urbanized and dry area) and the agricultural land. The higher heat flux in the used area led to stronger winds and further downward movement moving of the chemical agent than the farmland. The lateral dispersion of the chemical plume was emphasized in the Lagrangian Puff Model because it adopted Gaussian distribution.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2002년도 총회 및 춘계학술발표회
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• pp.122-126
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• 2002

Contaminant transport in porous media is characterized by solving an advection-dispersion equation(ADE). The ADE can cover equilibrium phenomena of interest, which include sorption, decay, and chemical reactions. Among these phenomena, sorption mechanism is described by several types of sorption isotherm. If we assume the sorption isotherm as linear, the solution of ADE can be easily procured. However, if we consider the sorption isotherm as non-linear isotherm like a Dual Reactive Domain Model (DRDM), the resulting differential equation becomes non-linear. In this case, the solution of ADE cannot be easily acquired by an analytic method. In this paper, we present the numerical analysis of ADE using a DRDM. The results reveal that even if sorption data may be fitted well using linear or non-linear isotherm, the characteristics of contaminant transport of the two cases are different from each other. To be concrete, the retardation of linear isotherm has stronger effect than that of the DRDM. As the non-linearity of sorption isotherm increases, the difference of retardation effects of the two cases becomes larger. For a pulse source, the maximum concentration of the linear model is higher than that of the DRDM, but the plume of the DRDM moves faster than that of the linear model. Behaviors of contaminant transport using the DRDM are consistent with common features of a linear model. For instance, biodegradation effect becomes larger as time goes by The faster the seepage velocity is, the faster the plume of contaminant moves. The plume of the contaminant is distributed evenly over overall domain in the event of high dispersion coefficient.

• Korean Journal of Hydrosciences
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• 제6권
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• pp.51-66
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• 1995

Various Eulerian-Lagerangian numerical models for the one-dimensional longtudinal dispersion equation are studied comparatively. In the models studied, the transport equation is decoupled into two component parts by the operator-splitting approach ; one part governing advection and the other dispersion. The advection equation has been solved using the method of characteristics following flud particles along the characteristic line and the result are interpolated onto an Eulerian grid on which the dispersion equation is solved by Crank-Nicholson type finite difference method. In solving the advection equation, various interpolation schemes are tested. Among those, Hermite interpo;ation po;ynomials are superor to Lagrange interpolation polynomials in reducing both dissipation and dispersion errors.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.490-491
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• 2007

We have investigated dielectric dispersion and absorption in organic light-emitting diodes using 8-hydroxyquinoline aluminum($Alq_3$) as an electron transport and emissive material. We analyzed the dielectric dispersion and absorption of organic light emitting diodes using impedance characteristics measurement by the auto-balancing bridge technique of ITO/$Alq_3$/Al. Impedance characteristics was measured complex impedance Z and phase e in the frequency range of 40Hz to $10^8Hz$. We obtained dielectric constant and loss tangent (tan $\delta$) of the device. From these analyses, we are able to interpret a dielectric dispersion and dielectric absorption contributed by an interfacial and orientational polarization.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2039-2049
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• 2024

The radioactive pollutant could migrate to the downstream urban area under the action of atmospheric dispersion due to the turbulent mixing under actual pollution accidents. A scenario in which radioactive contaminants from the upstream (for example, a nearshore nuclear power plant accident) migrates to the downstream urban blocks have been considered in this study. Numerical simulations using computational fluid dynamics (CFD) are then conducted to investigate the effects of the urban morphology (building packing density and layout) on the atmospheric dispersion of radioactive pollutants in this scenario. The building packing density and structure can significantly affect urban areas' mean flow pattern and the turbulent kinetic energy (TKE). The flow pattern and the TKE distribution influence the radioactive pollution dispersion. It is found that the radioactive pollution at the urban canyons is significantly affected by the vertical transport at the canyon. A comparison of the distributions of radioactive and traditional non-radioactive pollutants is also provided.