• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2004년도 총회 및 춘계학술발표회
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• pp.57-62
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• 2004

Streamline simulation researches have been extensively accomplished due to the swiftness of computation and the reduction of numerical dispersion. In this study, we developed a streamline simulation model using a semianalytical solution of ID transport equation. To validate accuracy of the developed model, we compared simulation results of contaminant transport, which were acquired by streamline simulation models using an analytical solution, a numerical solution, and a semianalytical solution. The developed model using the semianalytical solution matched well with the model using an analytical solution. However, streamline simulation model using a numerical solution showed numerical dispersion. For an advection-dominant flow, there was little difference in the simulation results between the developed model and tile analytical model, but the differences between the analytical model and the numerical model were cleary shown. From the comparison of computing time we know that the streamline simulation using the semianalytical solution is 2-60 times as fast as the streamline simulation using the numerical solution.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.1060-1067
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• 2006

Sandy soils are generally used as a capping material to reduce the pollutants transport from the contaminated dredged sediment. However, dredged material capping is not widely used because regulatory agencies are concerned about the potential for contaminants migration through the cap. Movement of contaminated pore water from sediment into cap is mainly related to sediment consolidation during and after cap placement. To evaluate the significance of consolidation induced transport of contaminants from sediment into cap, research centrifuge tests were conducted. Centrifuge test results illustrate that advection and dispersion are the dominant contaminants transport processes and that capping reduces the potential of contaminant migration from the dredged sediment effectively.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.799-802
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• 2008

General behaviors based on hydraulic characteristics of natural streams and channels have been recently analyzed and developed via various numerical models. However in the states of natural hydraulics, an experimental research must be performed simultaneously with the mathematical analysis due to effects of hydraulic properties such as meander, sediment, and so on. In this study based on 2-D advection-dispersion equation, flow and tracer experiments were performed in the S-curved meandering laboratory channel with a rectangular cross-section. The channel was equipped with instrument carriages which was equipped with an auto-traversing system to be used with velocity measuring sensors throughout the depth and breadth of the flow field. To measure concentration distribution of the salt solution was adjusted to that of the flume water by adding methanol and a red dye (KMnO4) was added to aid the visualization of the tracer cloud, the tracer was instantaneously injected into the flow as a full-depth vertical line source by the instantaneous injector and the initial concentration of the tracer was 100,000 mg/l. The secondary current as well as the primary flow pattern was analyzed to investigate the flow distribution in the meandering channels. The velocity distribution of the primary flow for all cases skewed toward the inner bank at the first bend, and was almost symmetric at the crossovers, and then shifted toward the inner bank again at the next alternating bend. Thus, one can clearly notice that the maximum velocity occurs taking the shortest course along the channel, irrespective of the flow conditions. The result of the tracer tests shows that pollutant clouds are spreading following the maximum velocity lines in each cases with various mixing patterns like superposition, separation, and stagnation of pollutant clouds. Flow characteristics in each cases performed in this study can be compared with tracer dispersion characteristics with using evaluation of longitudinal and transverse dispersion coefficients(LDC, TDC). As expected, LDC and TDC in meandering parts have been evaluated with increasing distribution and straight parts have effected to evaluate minimum of LDC and TDC due to symmetric flow patterns and attenuations of secondary flow.

• Korean Journal of Hydrosciences
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• 제5권
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• pp.85-97
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• 1994

A hybrid finite difference method for the longitudinal dispersion equation, which is based on combining the Holly-Preissmann scheme with fifth-degree Hermite interpolating polynomial and the generalized Crank-Nicholson scheme, is described and comparatively evaluated with other characteristics-based numerical methods. Longitudinal dispersion of an instantaneously-loaded pollutant source is simulated, and computational results are compared with the exact solution. The present method is free from wiggles regardless of the Courant number, and exactly reproduces the location of the peak concentration. Overall accuracy of the computation increases for smaller value of the weighting factor, $\theta$of the model. Larger values of $\theta$ overestimates the peak concentration. Smaller Courant number yields better accuracy, in general, but the sensitivity is very low, especially when the value of $\theta$ is small. From comparisons with the hybrid method using cubic interpolating polynomial and with splitoperator methods, the present method shows the best performance in reproducing the exact solution as the advection becomes more dominant.

• 대한토목학회논문집
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• 제14권1호
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• pp.131-141
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• 1994

특성곡선을 고려한 세가지 연산자 분리방법을 오염원의 종확산 문제에 적용하여, 그 결과를 Eulerian 기법들의 계산결과와 비교하였다. 연산자 분리방법의 이송방정식에 대한 수치 기법들로는 generalized upwind, two-point fourth-order 및 sixth-order Holly-Preissmann 기법들을 각각 적용하였으며, 확산 방정식에 대한 수치기법으로는 Crank-Nicholson 기법을 적용하였다. Holly-Preissmann 기법을 사용하는 연산자 분리방법들이 Eulerian 기법들에 비하여 매우 정확한 계산결과를 나타내었다. Eulerian 기법들의 경우에는 이송항의 근사방법으로서 중앙차분을 취하는 기법들은 수치진동을, 후방차분을 취하는 기법들은 수치분산을 각각 보였으며, 이러한 현상들은 종확산계수의 값이 작을수록 더욱 뚜렷하게 나타났다.

• 대한토목학회논문집
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• 제26권4B호
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• pp.335-344
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• 2006

본 연구에서는 Taylor의 이론, 즉 종방향 이송과 횡방향 확산이 서로 독립적으로 일어나며 두 과정이 서로 균형을 이룬다는 개념을 바탕으로 순차혼합모형을 제안하였다. 서로 다른 혼합시간과 유속 분포 등을 사용하여 수치모의를 실시하였으며, 여기서 얻어진 단면평균 농도분포를 1차원 종분산모형과 2차원 이송-분산 모형과 비교하였다. 그 결과, 순차혼합모형이 1차원 종분산모형으로 요약되는 Taylor의 이론을 잘 구현하고 있음을 알 수 있었다. 2차원이송-확산모형과의 비교를 통해 혼합 시간과 횡확산계수와의 관계를 밝힐 수 있었으며, 따라서 순차혼합모형이 1차원 종분산모형뿐 아니라 2차원 이송-분산모형까지 연계하여 전단류 분산을 통합적으로 설명하는 모형임을 알 수 있었다. 본 연구에서는 순차혼합모형의 수치모의 결과와 1차원 종분산모형과의 적합을 통해 종분산계수를 결정하고, 회귀식을 사용해 종분산계수 추정식을 제안하였다. 본 연구에서 제안한 종분산계수 추정식은 38개의 현장실험자료를 사용하여 검증하였다. 그 결과, 하폭 대 수심 비가 비교적 작은 하천에 대해서 높은 신뢰성을 나타내었으며, 대체적으로 기존의 경험식과 비슷한 신뢰도를 나타내었다.

• 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.

• 한국수자원학회논문집
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• 제32권6호
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• pp.607-616
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• 1999

비보존성 오염물질의 종확산에 관한 수치모형을 개발하였다. 계산기법으로는 종확산 방정식을 이송, 감쇠 및 확산 방정식으로 분리하고, 이들 방정식을 1/3 시간 간격에 대하여 번갈아 계산하는 단계분리 유한차분기법을 사용하였다. 이송방정식에 대해서는 Holly-Preissmann 기법을, 감쇠방정식에 대해서는 해석적 방법을, 확산방정식에 대해서는 Crank-Nicholson 기법을 각각 사용하였다. 오염물질이 불균일 흐름 내로 연속적으로 유입되는 경우 및 균일 흐름 내로 순간적으로 부하되는 경우에 대한 종확산 문제에 모형을 적용하여 계산결과를 정확해와 비교함으로써 모형을 검증하였다. 또한 감쇠방정식의 수치해법으로써 Euler 방법을 사용하는 기존의 모형에 계산결과를 비교하였다. 감쇠계수가 커질수록 본 모형이 기존의 모형에 비하여 더욱 정확한 계산결과를 나타내었다.

• 대한토목학회논문집
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• 제26권5B호
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• pp.557-562
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• 2006

준설작업으로 인해 재부유된 퇴적물로 구성된 탁도플륨의 이송확산 거동을 예측하기 위해 이(1998)가 제안한 수치 해석의 혼합방법(hybrid method)을 사용하여 3차원 수치모형을 개발하였다. 본 모형에서는 이송 및 확산식의 수치해석에 있어 이송 과정은 전방입자추적기법(forward particle-tracking method), 확산 과정은 유한차분기법을 사용하여 수치계산에 있어 무작위 행보(random walk) 방법에 비해 계산시간이 크게 단축되었으며, 수치모의 결과의 정확성도 크게 향상되었다. 본 모형을 검증하기 위하여 1, 2차원 해석해와의 비교, 그리고 Kuo 등(1985)의 3차원 수리해석모형의 계산결과와 비교하였다. 본 모형의 검증 결과는 비교적 해석해와 잘 일치하였다.

• 한국환경과학회지
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• 제8권3호
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• pp.355-361
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• 1999

The aim of this study is to develop the water quality simulation model (BAYQUAL) that deal with the physical, chemical and biological aspects of fate/behavior of pollutants in the bay. BAYQUAL is a two dimensional, time-variable finite element water quality model based on the flow simulation model in bay(BAYFLOW). The algorithm is composed of a hydrodynamic module which solves the equations of motion and continuity, a pollutnat dispersion module which solves the dispersion-advection equation. The applicability and feasibility of the model are discussed by applications of the model to the Kwangyang bay of south coastal waters of Korea. Based on the field data, the BAYQUAL model was calibrated and verified. The results were in good agreement with measured value within relative error of 14% for COD, T-N, T-P. Numerical simulations of velocity components and tide amplitude(M2) were agreed closely with the actual data.