• 한국지반공학회논문집
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• 제20권3호
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• pp.5-11
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• 2004

본 논문에서는 이류를 고려한 확산 실험을 통해 매립지 차수층을 이루는 점토와 실리카계와 석회계 두 종류의 고화재(PA, PB)에서의 무기물 이동특성을 알아보고 이를 순수확산 실험결과와 비교하였다. 점토와 고화층(PA, PB)에 대한 이류를 고려한 확산실험 결과 평균분산계수는 각각 $4.39\times l0^{-10}\textrm{m}^2 /s,\; 1.98\times l0^{-10}\textrm{m}^2 /s,\; 1.99\times l0^{-10}\textrm{m}^2 /s$ 로 나타나 고화층이 점토보다 높은 것으로 나타났다. 이류확산 실험 결과와 순수확산 실험결과를 비교 분석결과 이류를 고려한 경우 각각의 무기물에 대한 음이온인 염소이온의 분산계수의 값은 두 시험 결과 사이에 큰 차이를 나타내지 않았으나 범위는 이류를 고려한 경우가 순수확산의 경우 보다 적은 것으로 나타났다.

• Korean Chemical Engineering Research
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• 제57권2호
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• pp.289-300
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• 2019

We have conducted a preliminary numerical analysis to understand the effects of double-diffusive convection on the molar flux at the crystal region during the growth of mercurous bromide ($Hg_2Br_2$) crystals in 1 g and microgravity (${\mu}g$) conditions. It was found that the total molar fluxes decay first-order exponentially with the aspect ratio (AR, transport length-to-width), $1{\leq}AR{\leq}10$. With increasing the aspect ratio of the horizontal enclosure from AR = 1 up to Ar = 10, the convection flow field shifts to the advective-diffusion mode and the flow structures become stable. Therefore, altering the aspect ratio of the enclosure allows one to control the effect of the double diffusive natural convection. Moreover, microgravity environments less than $10^{-2}g$ make the effect of double-diffusive natural convection much reduced so that the convection mode could be switched over the advective-diffusion mode.

• 한국결정성장학회지
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• 제13권4호
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• pp.187-198
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• 2003

Zinc selenide (ZnSe) single crystals hold promise for many electro-optics, acousto-optic and green laser generation applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method based on the dissociative sublimation. We investigate the effects of diffusive-convection on the crystal growth rate of ZnSe with a low vapor pressure system in a horizontal configuration. Our results show that for the ratios of partial pressures, s=0.2 and 2.9, the growth rate increases with the Peclet number and the temperature differences between the source and crystal. As the ratio of partial pressures approaches the stoichiometric value of 2, the rate increases. The mass fluk based on one dimensional (1D model) flow for low vapor pressure system fall within the range of the predictions (2D model) obtained by solving the coupled set of conservation equations, which indicates the flow fields would be advective-diffusive. Therefore, the rate and the flow fields are independent of gravity acceleration levels.

• 한국해안해양공학회:학술대회논문집
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• 한국해안해양공학회 1995년도 정기학술강연회 발표논문 초록집
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• pp.108-109
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• 1995

Hypoxia has persisted during summer in the bottom water of the lower portion of the Rappahannock Estuary, a western shore tributary of Chesapeake Bay. A laterally integrated two-dimensional, real-time model, consisting of linked hydrodynamic and water quality models, was developed to study the contributing processes for hypoxia. The hydrodynamic model gives the information of physical transport processes, both advective and diffusive, to the water quality model, which simulates the spatial and temporal distributions of eight water quality state variables. (omitted)

• 한국결정성장학회지
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• 제29권3호
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• pp.107-114
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• 2019

A computational analysis has been carried out to get a thorough and full understanding on the effects of convective process parameters on double-diffusive convection during the growth of mercurous bromide ($Hg_2Br_2$) crystals on earth and under ${\mu}g$ conditions. The dimensional maximum magnitude of velocity vector, ${\mid}U{\mid}_{max}$ decreases much drasticlly near Ar = 1, and, then since Ar = 2, decreases. The ${\mu}g$ conditions less than $10^{-2}g$ make the effect of double-diffusion convection much reduced so that adequate advective-diffusion mass transfer could be obtained.

• 한국결정성장학회지
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• 제14권5호
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• pp.226-232
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• 2004

One predicts the crystal growth rate of ZnSe with a low vapor pressure system in a horizontal configuration based on one dimensional advection-diffusion and two-dimensional diffusion-convection model. The present results show that for the ratios of partial pressures, s = 0.2 and 2.9, the growth rate increases with the temperature differences between the source and crystal. As the ratio of partial pressure approaches the stoichiometric value, s = 2 from s = 1.5 (zinc-deficient case: s < 2) and 2.9 (zinc-rich case: s > 2), the rate increases sharply. For the ranges from 1.5 to 1.999 (zinc-deficient case: s < 2) and from s = 9 to 2.9 (zinc-rich case: s > 2), the rate are slightly varied. From the viewpoint of the order of magnitude, the one-dimensional model for low vapor pressure system falls within the 2D predictions, which indicates the flow fields would be advective-diffusive. For the effects of gravitational accelerations on the rate, the gravitational constants are varied from 1 g to $10^{-6}$ g for $\Delta$T = 50 K and s = 1.5, the rates remain nearly constant, i.e., 211 mg/hr, which indicates Stefan flow is dominant over convection.

• 한국환경보건학회:학술대회논문집
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• 한국환경보건학회 2002년도 춘계 국제 학술대회
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• pp.9-12
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• 2002

Diffusive transport of volatile organic compounds(VOCs) and their degradation by bacteria in unsaturated soils are couple by poorly understood mass transfer kinetics at the gas/water interface. Determination of the fate of VOCs in unsaturated soil is necessary to evaluate the feasibility of natural attenuation as a VOC remediation strategy. The objective of this study was to develop a mechanistically based mathematical model that would consider the interdependence of VOC transport, microbial activity, and sorptive interaction in a moist, unsaturated soil. Because the focus of the model was on description of natural attenuation, the advective VOC transport that is induced in engineered remediation processes such as vapor extraction was not considered. The utility of the model was assessed through its ability to describe experimental observations form diffusion experiments using toluene as a representative VOC in well-defined soil columns that contained a toluene degrading bacterium, Pseudomonas Putida, as the sole active microbial species. The coefficient for gas-liquid mass-transfer, K$\sub$LA/, was found to be a key parameter controlling the ability of bacteria to degrade VOCs. This finding indicates that soil size and geometry are likely to be important parameters in assessing the possible success of natural attenuation of VOCs in contaminated unsaturated soils.

• 한국해양학회지
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• 제30권6호
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• pp.543-549
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• 1995

연속된 AVHRR/SST 자료를 이용한 표층유속의 추정에 역행렬법이 이용되어 왔다. 본 모델에서 방정식체계는 열방정식과 제한요소로서 가중치가 있는 발산최소화이다. 제한요소는 열방정식의 속도해중에서 null space(Menke, 1984)에 해당하는 해를 구하기 위하여 도입되었으며 이 식들은 격자화한 영역에서 AVHRR/SST의 수온경사에 의해 선형화된다. 실험은 열방정식에 대한 발산최소화의 상대적 중요성을 나타내는 가중치의 크기를 설정하기 위하여 수행하였으며 행렬식은 SVD(Singular Value Decomposion)에 의해 해를 구했다. 실험에서 가상온도분포의 수온경사와 가상유속장의 발산의 크기는 실제해역에 근사시켰다. 열방정식은 착산의 효과를 무시하고 열속이 공간적으로 일정한 것으로 가정하여 구성하였으며 이와같은 가정에 의한 오류를 고려하기 위하여 가상 온도자료에 무작위오류를 도입하였다. 실험결과에 의하면 가중치를 설정하는 기준으로서 상대오차 최소화가 잔차최소화보다 바람직한 것으로 나타났으며 가중치가 $10^{-1}$의 크기일 때 추정유속의 오류가 가장 작은것으로 나타났다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제16권3호
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• pp.17-27
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• 2011

Recently, a physically based model of water-table fluctuation due to precipitation is developed based on aquifer water balance model. In the model, it was assumed that the water infiltration into ground surface is advection dominant and immediately reaches to water-table. The assumption may be suited for the sites where the water-table is shallow and/or the permeability of the unsaturated zone is high. However, there are more cases where the model is not directly applicable due to thick and low permeable unsaturated zone. For the low permeability unsaturated zone, the pattern of water flux passing through unsaturated zone is diffusive as well as advective. In this study, to improve the previously developed water-table fluctuation model, we combined the delayed drainage model, which has long been used in well hydraulics, to the water-table fluctuation model. To test the validity of the development, we apply the developed model to 5 different domestic sites. The model parameters are calibrated based on the groundwater hydrograph and the precipitation time series, and the correlation analyses among the parameters are pursued. The overall analyses on the delineated model parameters indicate that the delayed drainage parameters or delay index used in the developed model are able to reveal drainage information in the unsaturated zones.

• 한국해안·해양공학회논문집
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• 제33권1호
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• pp.13-29
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• 2021

본 연구에서는 해수의 유동에 관한 3차원 수치모델을 사용하여 경기만 한강 하구에서의 염 수송에 대한 메커니즘을 분석하였다. 수치모델의 모의 기간은 갈수기와 홍수기를 포함하는 2020년 1월 20일부터 9월 20일까지 약 245일이며, 모델 결과와 관측 자료의 비교를 통해 해수의 유동 및 염분 변화에 관한 수치모델의 재현성을 입증하였다. 한강 하구에서 염의 교환이 활발하게 이루어지는 염하수로의 북단과 남단 지역에 대해서 염 수송량(FS)을 산출하였다. 염 수송에 대한 발생 기작을 세부적으로 분석하기 위해 FS를 담수 유입에 의한 염의 이류 수송(QfS0), 수평 및 수직적인 유속 차이에 의한 염의 확산 수송(FE), 조석 변동성을 가진 유속과 염분의 위상 차이에 의한 염의 수송(FT)으로 분해하였다. 갈수기와 홍수기의 월 평균 염 수송량에 의하면, 두 기간 모두 외해로부터 한강 하구 지역으로 유입되는 염의 대부분은 FT에 의하여 강화도 남부 수로를 통해 수송된다. 반면에, 한강 하구로부터 외해로 유출되는 염의 대부분은 QfS0에 의하여 영종도 동부 수로를 통해 수송된다. 한강 하구에서 평균적인 염의 수송은 갈수기 동안 FT에 의하여 한강 하구의 상류 방향으로 수송되며, 홍수기 동안 QfS0에 의하여 외해 방향으로 수송된다. 결과적으로, 경기만 한강 하구에서의 염 수송은 외해 방향의 수송을 발생시키는 QfS0와 한강 상류 방향의 수송을 발생시키는 FT의 상호작용에 의하여 결정된다.