• 한국환경과학회지
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• 제4권2호
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• pp.169-180
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• 1995

This Daper presents effective simulation of the dispersion of thermal discharge which can be relesed at Boryong power plant. Applied numerical models are finite difference method for hydrodynamic analysis and Masch-model comprised of conditions for ambient current velocity. Application of these models is done in Cheonsu Bay Summing up the results of this study are as follows; 1. It is found that the result for measurements of temperature appears high at southwardly Songdo on flood. The reason is that tidal currents which flowed north direction were accompanied with southwardly dispersed thermal discharge. A minute Particle of thermal Plume has a tendency to dispels inward Deacheon Bay. 2. According to the results of numerical experiment, maximum distance for thermal discharge dispersion appeared 10.8 km at lower part and 8.6 km at upper part with power plant outlet as starting point. 3. Comparative the numerical simulation and Airbone Multispectral Scanner indicated that thermal discharge should be verified separative phenomena. The simulated results were compared with field data set showing good agreement. It is concluded that these model can be simulated well.

• Wind and Structures
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• 제4권1호
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• pp.31-44
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• 2001

Mean concentrations of ammonia gas released as a tracer from an isolated low-rise building have been measured and predicted. Predictions were calculated using computational fluid dynamics (CFD) and two dispersion models: a diffusion model and a Lagrangian particle tracking technique. Explicit account was taken of the natural variation of wind direction by a technique based on the weighted summation of individual steady state wind direction results according to the probability density function of the wind direction. The results indicated that at distances >3 building heights downstream the weighted predictions from either model are satisfactory but that in the near wake the diffusion model is less successful. Weighted solutions give significantly improved predictions over unweighted results. Lack of plume spread is identified as the main cause of inaccuracies in predictions and this is linked to inadequate resolution of flow features and mixing in the CFD model. Further work on non-steady state simulation of wake flows for dispersion studies is recommended.

• 한국수자원학회논문집
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• 제34권5호
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• pp.499-509
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• 2001

자연하천에서의 이송-확산 과정의 모의를 위하여 입자위치의 이산확률분포에 기초한 2차원 수송 모형을 개발하였다. 제안된 모형에서는 단위 시간간격동안 격자간의 질량이송을 예측하기 위하여 평균과 분산의 함수로 나타내어진 확률분포를 사용하였다. 개발된 모형은 유속, 확산계수, 단면적이 일정한 단순영역에 대하여 수치확산이 없는 해를 구하였고, 양의 확률을 만족시키는 안정조건이 성립한다면, 해석해와 다른 유한차분법과 비교하였을 때, 좋은 결과를 나타내었다. 본 모형의 현장적용성을 검토하기 위하여 캐나다에 위치한 Grand River를 대상을 얻은 수치실험 결과를 정상상태의 색소실험 결과와 비교하였다. 그 결과로서 본 모형은 자연하천에서의 2차원 이송-확산을 잘 모의할 수 있는 것으로 나타났다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(2)
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• pp.1457-1457
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• 2005

• 한국입자에어로졸학회지
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• 제13권4호
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• pp.173-182
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• 2017

An Eulerian-Lagrangin approach is used to compute particle dispersion from a power plant chimney. For air flow, three-dimensional incompressible filtered Navier-Stokes equations are solved with a subgrid-scale model by integrating the Newton's equation, while the dispersed phase is solved in a Lagrangian framework. The velocity ratios between crossflow and a jet of 0.455 and 0.727 are considered. Flow fields and particle distribution of both cases are evaluated and compared. When the velocity ratio is 0.455, it demonstrates a Kelvin-Helmholtz vortex structure above the chimney caused by the interaction between crossflow and a jet, whereas the other case shows flow structures at the top of the chimney collapsed by fast crossflow. Also, complex wake structures cause different particle distributions behind the chimney. The case with the velocity ratio of 0.727 demonstrates strong particle concentration at the vortical region, whereas the case with the velocity ratio of 0.455 shows more dispersive particle distribution. The simulation result shows similar tendency to the experimental result.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2377-2386
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• 2021

To model the atmospheric dispersion of radionuclides released from nuclear accident is very important for nuclear emergency. But the uncertainty of model parameters, such as source term and meteorological data, may significantly affect the prediction accuracy. Data assimilation (DA) is usually used to improve the model prediction with the measurements. The paper proposed a parameter bias transformation method combined with Lagrangian puff model to perform DA. The method uses the transformation of coordinates to approximate the effect of parameters bias. The uncertainty of four model parameters is considered in the paper: release rate, wind speed, wind direction and plume height. And particle swarm optimization is used for searching the optimal parameters. Twin experiment and Kincaid experiment are used to evaluate the performance of the proposed method. The results show that the proposed method can effectively increase the reliability of model prediction and estimate the parameters. It has the advantage of clear concept and simple calculation. It will be useful for improving the result of atmospheric dispersion model at the early stage of nuclear emergency.

• Journal of Mechanical Science and Technology
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• 제17권7호
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• pp.1054-1062
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• 2003

The numerical simulations of flow and pollutant particle dispersion are described for two-dimensional bell shaped hills with various aspect ratios. The Reynolds-averaged incompressible Navier-Stokes equations with low Reynolds number $\kappa$-$\varepsilon$ turbulent model are used to simulate the flowfield. The gradient diffusion equation is used to solve the pollutant dispersion field. The code was validated by comparison of velocity, turbulent kinetic energy, Reynolds shear stress, speed-up ratio, and ground level concentration with experimental and numerical data. Good agreement has been achieved and it has been found that the pollutant dispersion pattern and ground level concentration have been strongly influenced by the hill shape and aspect ratio, as well as the location and height of the source.

• 대기
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• 제23권1호
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• pp.93-102
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• 2013

Atmospheric transport pathway of an air mass is an important constraint controlling the chemical properties of the air mass observed at a designated location. Such information could be utilized for understanding observed temporal variabilities in atmospheric concentrations of long-lived chemical compounds, of which sinks and/or sources are related particularly with natural and/or anthropogenic processes in the surface, and as well as for performing inversions to constrain the fluxes of such compounds. The Lagrangian particle dispersion model FLEXPART provides a useful tool for estimating detailed particle dispersion during atmospheric transport, a significant improvement over traditional "single-line" trajectory models that have been widely used. However, those without a modeling background seeking to create simple back-trajectory maps may find it challenging to optimize FLEXPART for their needs. In this study, we explain how to set up, operate, and optimize FLEXPART for back-trajectory analysis, and also provide automatization programs based on the open-source R language. Discussions include setting up an "AVAILABLE" file (directory of input meteorological fields stored on the computer), creating C-shell scripts for initiating FLEXPART runs and storing the output in directories designated by date, as wells as processing the FLEXPART output to create figures for a back-trajectory "footprint" (potential emission sensitivity within the boundary layer). Step by step instructions are explained for an example case of calculating back trajectories derived for Anmyeon-do, Korea for January 2011. One application is also demonstrated in interpreting observed variabilities in atmospheric $CO_2$ concentration at Anmyeon-do during this period. Back-trajectory modeling information introduced in this study should facilitate the creation and automation of most common back-trajectory calculation needs in atmospheric research.

• 한국초전도ㆍ저온공학회논문지
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• 제20권2호
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• pp.11-15
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• 2018

In this study, a cancer treatment by accumulating and aggregating ferromagnetic particles in newborn blood vessels was examined. It is necessary for this treatment to control dispersion-aggregation property of ferromagnetic particles. Ferromagnetic particles required in this method disperse at low magnetic field, aggregate at high magnetic field and maintain the aggregation even after removal of the magnetic field. In order to control the dispersion-aggregation property, the surface of magnetite particles was modified with higher fatty acids having different lengths. As a result, we succeeded to prepare propionic acid-modified magnetite particles that form irreversible aggregation by magnetic field. The model experiments simulating newborn blood vessels showed that these particles can block the flow by the magnetic field, and the blockage was maintained after removal of the magnetic field.

• 한국해양환경ㆍ에너지학회지
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• 제11권1호
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• pp.13-23
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• 2008

연안해역의 부영양화, 빈산수괴 형성 그리고 유해적조류 출현과 같은 수질오염은 하계 담수의 대량유입에 의해 빈번하게 발생한다. 따라서 연안해역의 수질오염 현상을 정확히 예측하기 위해서는 담수가 해수유동에 의해 이송-확산되어 해역수질 및 생태계에 미치는 영향범위에 대한 예측 및 분석기술 개발이 필요하다. 본 연구에서는 GUI(Graphic User Interface)를 이용하여 연안해역 해수유동과 담수 확산을 쉽게 예측하고, 그 결과를 효과적으로 검토할 수 있는 소프트웨어를 개발하였다. 3차원 유한요소모형을 사용하여 조석에 의한 해수유동을 계산하였고, 담수 확산 계산에는 통계학적인 개념을 이용하여 담수 입자의 운동을 묘사하는 2차원 Random-Walk 모형을 사용하였다. 개발된 시스템을 이용하여 목포해역의 2차원 조류 분포와 담수 확산을 모의하였다. 사용한 입자추적모형의 검증을 위해 다른 이송확산 수치해석 방법에 의한 결과 및 1, 2차원 해석해와 비교하였다. 본 연구에서 개발한 예측시스템은 GUI 환경에서 작동되므로 누구나 쉽게 자료의 입력 및 수정이 가능하며, 계산된 모형결과를 그래픽을 이용해 효과적으로 가시화 하여 계산결과를 누구나 쉽고 정확하게 볼 수 있다. 따라서 본 시스템을 이용하여 연안해역으로 유입되는 담수의 확산 범위를 수시로 예측하여 신속하게 대책을 수립한다면, 오염된 담수유입으로 인한 인근해역의 환경피해를 줄일 수 있을 것이다.