• Nuclear Engineering and Technology
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• 제52권4호
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• pp.819-826
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• 2020

The method of the Laplace transform has been used to obtain an analytical solution of the three-dimensional steady state advection diffusion equation for the airborne radionuclide release from any nuclear installation such as the power reactor in an area source. The present treatment takes into account the removal of the pollutants through the nuclear reaction. We assume that the pollutants are emitted as a constant rate from the area source. This physical consideration is achieved by assuming that the vertical eddy diffusivity coefficient should be a constant. The prevailing wind speed is a constant in 𝑥- direction and a linear function of the vertical height z. The present model calculations are compared with the other models and the available data of the atmospheric dispersion experiments that were carried out in the nuclear power plant of Angra dos Reis (Brazil). The results show that the present treatment performs well as the analytical dispersion model and there is a good agreement between the values computed by our model and the observed data.

• 한국환경과학회:학술대회논문집
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• 한국환경과학회 2003년도 International Symposium on Clean Environment
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• pp.165-170
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• 2003

A significant surface net heat loss appears around the Kuroshio and the Tsushima Warm Current regions. The area where the surface heat loss occurs should require heat to be supplied by the current to maintain the long-term annual heat balance. Oceanic heat advection in these regions plays an important role in the heat budget. The spatial distribution of the heat supply by the Tsushima Warm Current near the surface was examined by calculating the horizontal heat supply in the surface layer of the East/Japan Sea, directly from historical sea surface temperature and current data. We have also found a simple estimation of the effective vertical scale of heat supply by the current to compensate net heat loss using the heat supplied by the current in the surface 10m layer. The heat supplied by the current for the annual heat balance was large in the Korea/Tsushima Strait and along the Japanese Coast, and was small in the northwestern part of the East/Japan Sea. The amount of heat supplied by the current was large in the northwestern part and small in the southeastern part of the East/Japan Sea. These features suggest that the heat supplied by the Tsushima Warm Current is restricted to near the surface around the northeastern part and extends to a deeper layer around the southeastern part of the East/Japan Sea.

• 대기
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• 제24권4호
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• pp.555-563
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• 2014

The impacts of dynamic and thermodynamic schemes used in the Community Ice CodE (CICE), the Los Alamos sea ice model, on sea ice concentration, extent and thickness over the Arctic and Antarctic regions are evaluated. Using the six dynamic and thermodynamic schemes such as sea ice strength scheme, conductivity scheme, albedo type, advection scheme, shortwave radiation method, and sea ice thickness distribution approximation, the sensitivity experiments are conducted. It is compared with a control experiment, which is based on the fixed atmospheric and oceanic forcing. For sea ice concentration and extent, it is found that there are remarkable differences between each sensitivity experiment and the control run over the Arctic and Antarctic especially in summer. In contrast, there are little seasonal variations between the experiments for sea ice thickness. In summer, the change of the albedo type has the biggest influence on the Arctic sea ice concentration, and the Antarctic sea ice concentration has a greater sensitivity to not only the albedo type but also advection scheme. The Arctic sea ice thickness is significantly affected by the albedo type and shortwave radiation method, while the Antarctic sea ice thickness is more sensitive to sea ice strength scheme and advection scheme.

• 한국수자원학회논문집
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• 제37권11호
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• pp.889-896
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• 2004

프랙탈 이송확산방정식은 정수 차수의 미분연산자로 구성된 고전적인 이송확산방정식과 비교하여 프랙탈 차수의 미분연산자로 구성된 보다 상위개념의 방정식으로써 정의된다. 지금까지의 프랙탈 이송확산방정식은 추계학적인 기법을 동원하여 푸리에-라플라스 공간에서 주로 해석되었으나, 본 연구에서는 실제 공간에서 유한차분개념을 도입하여 보다 직접적으로 하천에서의 오염물 이송확산에 관한 지배방정식을 유도하였다. 이러한 개념의 유도방법은 프랙탈 차수 및 관련 확산계수의 물리적인 추정에 관한 실마리를 제공할 수 있다. 고전적인 이송확산방정식과는 달리 프랙탈 이송확산방정식은 실제 하천에서 관측되는 오염물의 시간-농도 분포곡선의 왜곡현상과 분포곡선의 전후방부 농도를 보다 실제에 가깝게 모의할 수 있을 것으로 기대되어진다.

• 한국수산과학회지
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• 제30권6호
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• pp.1033-1043
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• 1997

In order to understand the generation mechanism of the Ulleung Eddy, we carried out a series of numerical experiments using the nonlinear 11/2 - layer model allowing the inflow of the Tsushima Current. According to our numerical results, the Ulleung Eddy was generated due to the inflow variations of the Tsushima Current. Its inflow through the Korea Strait was deflected to the east due to the Coriolis force and the nonlinear self advection. Thus, an anticyclonic motion was formed at the north of the Korea Strait. The inflow became a coastal boundary current, and finally flowed out model ocean through the eastern exit. When the speed of inflow decreased slowly, the eddy- like motion at the north of the Korea Strait changed into an enclosed anticyclonic eddy of about 200 km in diameter. The Ulleung Eddy became circular shape due to the nonlinear self advection, then changed into elliptical shape in meridional direction because of the blocking effect of the western boundary.

• 대기
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• 제24권2호
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• pp.141-150
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• 2014

This study investigates the characteristics of the Gross Moist Stability (GMS) over the tropics. The GMS summarizes the relationship between large-scale entropy forcing due to radiation and surface fluxes and the response of smaller-scale convection. The GMS is able to explain both to where moist entropy is advected by the atmospheric circulation and how deep the moisture flux convergence is in the tropical region. In the deep convective region, positive GMS appears over the warm pool region due to the strong column-integrated moisture convergence and the ensuing export of moist entropy to the environment. The vertical advection of moist entropy dominates over the horizontal advection in this region. Meanwhile, over the eastern tropical ITCZ region, which is characterized by shallow convective area, import of moist entropy by horizontal winds is dominant compared to the vertical moist entropy advection. Future changes in the GMS are also examined using the 22 CMIP5 model simulations. A decrease in the GMS appears widely across the tropics, but its increase occurs over the western-central equatorial Pacific. It is evident that the increased GMS region corresponds to an increased region of precipitation, implying that strengthened convection in the future due to increased entropy forcing exports the enhanced moist energy to stabilize the environment.

• 대기
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• 제28권4호
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• pp.383-392
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• 2018

This study investigates synoptic characteristics of cold surges over South Korea during winter season (December-February). A total of 63 cold events are selected by quantile regression analysis using daily mean temperature observations from 11 KMA stations for 38 years (1979/80-2016/17). Large-scale pressure pattern during the cold surges is well characterized by high over Siberia and low over Aleutian regions, which elucidates cold advection over the Korean peninsula. However, the large-scale pattern cannot successfully explain the observed sudden decrease of temperature during the cold surges. Composite analyses reveal that a synoptic-scale cyclone developing over the northern Japan is a key feature that significantly contribute to the enhancement of cold advection by increasing pressure gradient over the Korean peninsula. Enhanced sensible and latent heat fluxes are observed over the southern ocean of Korea and Japan during the cold surges due to temperature and humidity differences between the near surface and the lower atmosphere over the ocean. The evaporated water vapor transported toward the center of the surface cyclone and condenses in the lower-to-middle troposphere. The released energy likely promotes the development of the surface cyclone by inducing positive PV near the surface of the heating region.

• 한국가시화정보학회지
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• 제20권3호
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• pp.74-85
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• 2022

We propose a Cubic-Interpolated Pseudo-Particle Lattice Boltzmann method (CIP-LBM) for the convection-diffusion equation (CDE) based on the Bhatnagar-Gross-Krook (BGK) scheme equation. The CIP-LBM relies on an accurate numerical lattice equilibrium particle distribution function on the advection term and the use of a splitting technique to solve the Lattice Boltzmann equation. Different schemes of lattice spaces such as D1Q3, D2Q5, and D2Q9 have been used for simulating a variety of problems described by the CDE. All simulations were carried out using the BGK model, although another LB scheme based on a collision term like two-relation time or multi-relaxation time can be easily applied. To show quantitative agreement, the results of the proposed model are compared with an analytical solution.

• 한국수자원학회논문집
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• 제45권2호
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• pp.179-189
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• 2012

오염물질의 이동 현상을 모의하기 위하여, 감쇠항이 있는 3차원 이송-확산 방정식의 수치모형이 개발되었다. 개발된 모형은 유한차분 모형으로서 시간단계의 가중치 ${\alpha}$를 포함하는 음해법(implicit finite difference method)과, 반복법인 Gauss-Seidel SOR(successive over relaxation)이 사용되었다. 모형은 보다 단순화된 가정 하에서 존재하는 두 가지의 해석적인 해와 비교되었다. 그 결과 Peclet number가 5~20 이하에서는 수치 분산의 영향이 크지 않았고 작은 오차범위 내에서 해석적인 해와 동일하였다. 또한 가중치 ${\alpha}$의 변화에 대한 모형의 거동은 Crank-Nicolson 모형(${\alpha}$=0.5)이 fully-implicit 모형(${\alpha}$=1)보다 해석적인 해에 접근함을 보여주었다. 모형의 검증과 실효성 제고를 위하여, mass balance를 검토하였다. 즉, 이송, 확산 및 감쇠항 각각에 대한 질량 이동을 산출하였으며, 그 결과 질량 이동의 계산 오차는 약 3% 이내였다. 본 모형은 감쇠 과정이 수반되는 3차원 이송-확산의 농도분포와 질량이동을 산출할 수 있으며 다양한 경계조건을 설정함으로서 현장조건을 반영할 수 있다. 그러나본 모형은 고정격자를 기반으로하는 유한차분 모형이므로 Peclet number가 비교적 작게 나타날 수 있는 토양 및 지하수계의 오염물질 이동 등의 문제에서 유용하게 적용될 수 있을 것으로 사료된다.

• 정보처리학회논문지A
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• 제16A권6호
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• pp.419-426
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• 2009

일반적으로 사실성 있는 유체를 시뮬레이션하기 위해 Navier-Stokes 방정식을 사용한다. Euler 구조에서 Navier-Stokes 방정식을 풀 때, 이 류항은 비선형이어서 계산이 복잡하기 때문에 근사화한 모델로 Semi-Lagrangian 방법을 사용한다. Semi-Lagrangian 방법에서는 먼저 이류하 는 위치를추적하고, 추적한 위치에서 값을 보간해서 사용한다. Stam이 제안한 방법으로 계산할 경우, 이 과정에서 수치적 소실이 많이 발생하 기 때문에 수치적 소실을 보정하려는 노력들이 있어 왔다. 그러나 대부분의 경우에 보간하는 과정에서의 소실을 줄이려는 노력이거나, 입자를 같이 사용하는 방법이었다. 따라서 본 논문에서는 Euler 구조에서 다른 추가나 변형을 가하지 않고 이류항의 연산에서 추적법을 개선함으로 수 치적 소실을 줄이는 방법을 제안한다. 우리의 방법에서는 현재 격자의 속도로 역추적하는 기존의 방법이 아니라, 현재의 격자로 오게 될 속도 를 가진 격자를 찾아서, 그 격자의 물리량들을 선형 보간하여 사용한다. 이는 직관적으로 생각할 때, 어느 지점의 물리량은 그 지점의 속도로 인해 다음 단계에 다른 지점에 있게 된다는 사실을 그대로 적용한 것이다. 본 논문에서 제안한 방법으로 기체를 시뮬레이션 했을 때 수치적 소 실이 줄었으며, 그로 인해 사실성을 높이면서도 실시간 처리가 가능했다.