• 한국대기환경학회지
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• 제33권6호
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• pp.583-592
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• 2017

A method is proposed for locating the heat sources from temperature observations, and its applicability is investigated for urban thermal environment simulations. A Lagrangian particle dispersion model, which is originally built for simulating the pollutants spread in the air, is exploited to identify the heat sources by transporting the Lagrangian heat particles backwards in time. The urban wind fields are estimated using a diagnostic meteorological model incorporating the morphological model for the urban canopy. The proposed method is tested for the horizontally homogeneous urban boundary layer problems. The effects of the turbulence levels and the computational time on the simulation are investigated.

• ALGAE
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• 제34권4호
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• pp.315-326
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• 2019

Northeastward drifts of massive Sargassum patches were observed in the East China Sea (ECS) and Yellow Sea (YS) by the Geostationary Ocean Color Imager (GOCI) in May 2017. Coverage of the brown macroalgae patches was the largest ever recorded in the ECS and YS. Three-dimensional circulation modeling and Lagrangian particle tracking simulations were conducted to reproduce drifting trajectories of the macroalgae patches. The trajectories of the macroalgae patches were controlled by winds as well as surface currents. A windage (leeway) factor of 1% was chosen based on sensitivity simulations. Southerly winds in May 2017 contributed to farther northward intrusion of the brown macroalgae into the YS. Although satellite observation and numerical modeling have their own limitations and associated uncertainties, the two methods can be combined to find the best estimate of Sargassum patch trajectories. When satellites were unable to capture all patches because of clouds and sea fog in the ECS and YS, the Lagrangian particle tracking model helped to track and restore the missing patches in satellite images. This study suggests that satellite monitoring and numerical modeling are complementary to ensure accurate tracking of macroalgae patches in the ECS and YS.

• 한국해안해양공학회지
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• 제10권2호
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• pp.73-82
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• 1998

연안에서 표층 방류된 온수의 확산-이송을 모의하고자 배출구 인근의 근역에서는 반능동적 입자추적의 원리가 적용된 부작위행보모형과 원역에서는 Eulerian-Lagrangian 농도가 결합된 2차원 모형이 개발되었다. 근역에서 표층으로 부상되는 온수괴는 부력을 갖는 다수의 입자군으로 변환되어 초기 평면확산의 증가를 나타내고, 이러한 부력확산의 영향이 무작위행보의 기본식에 도입되었다. 개발된 모형의 초기평가는 단순한 지형의 해역과 실제해역에서 수행되었다. 단순해역에서는 부력이 고려되지 않는 중립입자모형의 결과에 비하여 초기 확산이 크게 나타나고, 기존 근역모형CORMIX3과 유사하나 외해측으로 확장된 성향을 보인다. 천수만에서 실제적용 결과도 배출구 근처에서 관측치에 유사한 퍼짐 효과가 나타나며 모형의 적용성이 인정된다.

• 한국해안해양공학회지
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• 제8권2호
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• pp.185-192
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• 1996

연안에서의 효율적인 확산해석을 위해 연산자 분리기법에 의한 Eulerian-Lagrangian 농도모형과 random walk 방법이 결합된 모형이 수립되었다 수립한 입자추적모형은 특히 고농도 변화 지역에서 오차 없이 만족스럽게 해석할 수 있는 수단으로 판단된다. 모형실험결과 오염원 방류초기의 ▽C$\geq$0.005에서 거의 정확해와 일치하는 결과를 얻었고, ▽C$\leq$0.002에서는 만족스럽지 못한 결과가 유도되어 입자추적모형의 적용한계의 기준으로 제시되었다. 따라서 실제 해역에서의 적용에서 고농도의 오염원이 발생되는 근역에서는 입자추적모형을 적용하고 이후의 전역에 대해서는 농도모형을 이용하여 해석상의 능률 제고와 정도의 향상을 도모할 수 있었다.

• 해양환경안전학회지
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• 제3권1호
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• pp.73-83
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• 1997

To predict the oil-spill dispersion in marine waters, the oil-spill dispersion model based on Lagrangian particle-tracking method was developed and applied to Kwangyang and Jinju Bay. The tidal current movements to be required as input data of the oil-spill dispersion model were obtained by a two-dimensional numerical tidal model. Evaluation of tidal current movements using mean tide was successful. Modelling results were compared with the field data obtained at spill site. There were some descrepancies between modeling results and field data. However, the general pattern of modelling results was similar to that of field data. Provided the real-time tidal currents and more accurate wind data are supported, more favorable results can be obtained.

• Nuclear Engineering and Technology
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• 제42권2호
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• pp.211-218
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• 2010

An analysis model on debris transport in the containment floor of pressurized water reactors is developed in which the flow field is calculated by Eulerian conservation equations of mass and momentum and the debris particles are traced by Lagrange equations of motion using the pre-determined flow field data. For the flow field calculation, two-dimensional Shallow Water Equations derived from Navier Stokes equations are solved using the Finite Volume Method, and the Harten-Lax-van Leer scheme is used for accuracy to capture the dry-to-wet interface. For the debris tracing, a simplified two-dimensional Lagrangian particle tracking model including drag force is developed. Advanced schemes to find the positions of particles over the containment floor and to determine the position of particles reflected from the solid wall are implemented. The present model is applied to calculate the transport fraction to the Hold-up Volume Tank in Advanced Power Reactors 1400. By the present model, the debris transport fraction is predicted, and the effect of particle density and particle size on transport is investigated.

• 한국해양공학회지
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• 제23권2호
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• pp.37-46
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• 2009

Typhoon Rusa in 2002 was recorded as causing the biggest damage due to flood in our country. With the enormous damage to the land, the flood was totally discharged to the open sea. As a result, in the coastal area, the discharging of a river had a big influence in comparison to the scale of the coastal area, which suffered damaged due to the discharging of the river. As it cleared the land, the load was totally discharging into the sea, where it caused various problems due to its influence on the ecosystem. These included changes to the environment, like a difference in salinity and the inflow of a land load. Therefore, in this study, a Lagrangian particle tracking model was constructed using a flow model capable of solving the behavior of a river plume, supposing Sachon Bay. It is performed the research able to tendency-like valuation and reappearance about real event. The result was that the model was well approximated the sea area tendency and the river plume of the specific event.

• 한국해안해양공학회지
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• 제10권1호
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• pp.37-44
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• 1998

본 연구에서 제안하는 혼합 방법(hybrid method)은 흐름이 우세한 영역에서의 전송 문제를 정확하고 효과적으로 해결하기 위하여 개발된 것으로 오일러-라그란쥐적 방법과는 달리 전방추적에 의하여 이송 과정이 수행되므로 보간 기법이 불필요하고 무작위 행보에 의한 라그란쥐적 방법과 달리 유한 차분법에 의하여 확산 과정이 수행되므로 많은 입자가 요구되지도 않는다. 한 점에 순간적으로 부하되는 오염원과 연속적으로 부하되는 오염원에 대한 이론적인 해와 비교하여 확산 계수와 무관하게 상당히 만족할 만한 결과를 얻었다. 현 방법은 또한 2차원 상에서 주변 5격자로부터 보간하는 오일러-라그란쥐적 방법과 무작위 행보로 입자 추적하는 순수 라그란쥐적 방법과 비교하여 정확성은 물론 계산 시간에 있어서도 상당히 월등한 방법임이 입증되었다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.173-175
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• 2015

We simulate the particle bed motions with combustion and reduction in steel making rotary kilns. The particle bed motions are simulated by a Lagrangian approach called Discrete Phase Model (DPM). To reduce the number of tracking particles, the Coarse Grain Model (CGM) was applied. The model for particle motions showed good agreements with experimental results. In addition to the particle motion, the combustion and reduction simulation was performed. The combustion and reduction simulation can consider heat, mass and momentum transfer between the gas phase and particle beds.

• 대한기계학회논문집B
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• 제29권6호
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• pp.687-695
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• 2005

On the notion that the Reynolds stresses are transported with different time scale depending on the transport direction, the third order velocity correlations are represented by a new turbulent gradient transport model with tonsorial Lagrangian time scale. In order to verify the proposed model, DNS data are first obtained in a turbulent channel flow at Re = 180 and tonsorial Lagrangian time scales are computed. The present model predictions are compared with DNS data and those predicted by the third-order turbulent transport model of Hanjalic and Launder that uses a scalar time scale. The result demonstrates that the Reynolds stresses are indeed transported with different time scale depending on the transport direction.