• Nuclear Engineering and Technology
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• v.29 no.6
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• pp.459-467
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• 1997

The steady-state behavior of recycling neutral atoms in a tokamak edge region has been analyzed through a two-dimensional Monte Carlo simulation. A particle tracking algorithm used in earlier research on the neutral particle transport is applied to this Monte Carlo simulation in order to perform more accurate calculations with the EDGETRAN code which was previously developed for a two-dimensional edge plasma transport in the authors' laboratory. The physical model of neutral recycling includes charge-exchange and ionization interactions between plasmas and neutral atoms. The reflection processes of incident particles on the device wall are described by empirical formulas. Calculations for density, energy, and velocity distributions of neutral deuterium-tritium atoms have been carried out for a medium-sized tokamak with a double-null configuration based on the KT-2 conceptual design. The input plasma parameters such as plasma density, ion and electron temperatures, and ion fluid velocity are provided from the EDGETRAN calculations. As a result of the present numerical analysis, it is noticed that a significant drop of the neutral atom density appears in the region of high plasma density and that the similar distribution of neutral energy to that of plasma ions is present as frequently reported in other studies. Relations between edge plasma conditions and the neutral recycling behavior are discussed from the numerical results obtained herein.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.55 no.6
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• pp.954-959
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• 2022

Marine outfalls are used to discharge treated liquid effluents to the environment. An efficiently designed, constructed and operated marine outfall effectively dilutes the discharged effluent, thereby reducing the risk to biota and humans dependent upon the marine environment. In this study, we investigated the effluent transport from a marine outfall at different depths in Masan Bay. A particle-tracking model was used to predict the dispersion of effluent. The model results indicate that some particles released from a depth of 13 m move to the inner area of Masan Bay within 48 h. As the release depth increases after 48 h, the particles move further southward. This suggests that effluent from the outer area of Masan Bay can affect the inner area, and that this effect can be reduced by increasing the depth of effluent release.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.27-30
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• 2001

Flow and transport at fracture intersections, and their effects on network scale transport, are investigated in three-dimensional random fracture networks. Fracture intersection mixing rules complete mixing and streamline routing are defined in terms of fluxes normal to the intersection line between two fractures. By analyzing flow statistics and particle transfer probabilities distributed along fracture intersections, it is shown that for various network structures with power law size distributions of fractures, the choice of intersection mixing rule makes comparatively little difference in the overall simulated solute migration patterns. The occurrence and effects of local flows around an intersection (local flow cells) are emphasized. Transport simulations at fracture intersections indicate that local flow circulations can arise from variability within the hydraulic head distribution along intersections, and from the internal no flow condition along fracture boundaries. These local flow cells act as an effective mechanism to enhance the nondiffusive breakthrough tailing often observed in discrete fracture networks. It is shown that such non-Fickian (anomalous) solute transport can be accounted for by considering only advective transport, in the framework of a continuous time random walk model. To clarify the effect of forest environmental changes (forest type difference and clearcut) on water storage capacity in soil and stream flow, watershed had been investigated.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.4
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• pp.67-82
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• 2003

A 2-dimensional hydrodynamic model has been applied to understand water circulation pattern in Lake Deacheong. The simulation results have been used in sediment transport modeling. A sediment transport model using a particle tracking method has been developed to simulate sediment transport in the ocean, river and reservoir. The model was applied to estimate transport track of particulate pollutants in the lake. The hydrodynamic model was verified for water level variations and showed good agreements. Through the results we found out that water velocity is less than 5 cnysec for mean yearly flow and more than 120 cnysec at some points for the simulated flood flow. The incoming sediment particles in flood season reached into the Daecheong Dam. But the incoming sediment particles in the mean flow were settled down at riverbed and didn't move into the dam. These results can be used in setting up water quality management plan in the lake.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2006.10a
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• pp.43-46
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• 2006

• Proceedings of the Korean Nuclear Society Conference
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• 2001.10a
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• pp.57-57
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• 2001

• Proceedings of the Korea Water Resources Association Conference
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• 2003.05b
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• pp.759-762
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• 2003

• Journal of computational fluids engineering
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• v.21 no.2
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• pp.81-89
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• 2016

Numerical simulations are carried out for the fluid flow and particle transport around two nearby circular cylinders in a side-by-side arrangement. The present study aims to understand the effects of the particle Stokes number and the spacing between two cylinders on particle dispersion and deposition characteristics. Simulations are based on an Eulerian-Lagrangian approach where the motion of particles is calculated by a Lagrangian approach based on one-way coupling. Results show that the flow structure is very different depending on the cylinder spacing, eventually affecting the overall pattern of particle dispersion significantly. It is also found that particles with smaller Stokes number tend to be distributed more uniformly in the wake of two cylinders, being located even inside the vortex cores. Meanwhile, particle deposition is analyzed in terms of the deposition efficiency and deposition location. The deposition efficiency of particles strongly depends on the Stokes number, whereas it is slightly affected by the cylinder spacing. The deposition location gets wider as the Stokes number increases, and it becomes asymmetric about the center of each cylinder as the cylinders get close.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.1
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• pp.26-33
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• 1999

Coastal sediments in polluted areas adsorb many hydrophobic pollutants such as PCBs. During environmental remediation projects like dredging, they can be resuspended and transported to less polluted areas. To assess the environmental impact, the author previously developed a mathematical model that can simulate the changes of particle size distribution (PSD) due to sedimentation, vortical dispersion and coagulation. In this research, the simulation results using this model were presented in conjunction with observed PSDs from a 2-m settling column simulating coastal environments. The simulations showed that the model predictions were in fairly good agreement with the observed data (changes of PSDs in terms of depths and times), and that the resuspended sediments coagulated during the vertical transport. So, this study showed that the developed model has a good ability to describe the very complicated phenomena of real aggregation and vortical transport dynamics of coastal sediments with various particle sizes.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.116-118
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• 2002

It has been noted that Monte Carlo simulations are the most accurate method to calculate dose distributions in any material and geometry. Monte Carlo transport algorithms determine the absorbed dose by following the path of representative particles as they travel through the medium. Accurate Monte Carlo dose calculations rely on detailed modeling of the radiation source. We modeled the effects of beam modifiers such as collimators, blocks, wedges, etc. of our accelerator, Varian Clinac 600C/D to ensure accurate representation of the radiation source using the EGSnrc based BEAM code. These were used in the EGSnrc based DOSXYZ code for the simulation of particles transport through a voxel based Cartesian coordinate system. Because Monte Carlo methods use particle-by-particle methods to simulate a radiation transport, more particle histories yield the better representation of the actual dose. But the prohibitively long time required to get high resolution and accuracy calculations has prevented the use of Monte Carlo methods in the actual clinical spots. Our ultimate aim is to develop a Monte Carlo dose calculation system designed specifically for radiation therapy planning, which is distinguished from current dose calculation methods. The purpose of this study in the present phase was to get dose calculation results corresponding to measurements within practical time limit. We used parallel processing and some variance reduction techniques, therefore reduced the computational time, preserving a good agreement between calculations of depth dose distributions and measurements within 5% deviations.