• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.92.1-92.1
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• 2015

열전소재의 열전성능을 평가하기 위해서는 샘플 내 상하부 온도구배가 필요하다. 하지만 진공챔버 내에서는 대류효과가 제한되어, 1 mm 이하 두께의 얇은 샘플은 상하부 방향으로 온도 구배를 조성하기 어렵다. 온도 구배를 조성하기 위해서는 샘플의 두께 방향을 관통하는 열유속이 필요하며, 진공 분위기에서 열유속을 조성하기 위해서는 히터뿐만 아니라 별도의 열배출기가 요구된다. 본 연구에서는 열전특성 측정 장비 내 수냉식 열배출기의 설계를 위해, 열배출기의 층수를 달리하며 열전달거동을 수치해석적인 방법으로 연구하였다. 열배출기의 층수에 따른 영향을 평가하기 위해서 동일한 채널길이를 유지시키면서 층수를 달리하는 기하학적인 구조들을 설계하였다. 수치해석을 용이하게 진행하기 위해, 열배출기의 형태는 단순한 bar 형태를 가진 1-5층의 다층 구조 로 설계하였다. 열배출기들 각각의 열전달 효율을 평가하기 위해, 수냉식 열배출기의 열배출량에 가장 큰 영향을 미치는 질량유량을 0.1-1 g/s로 변화 시키면서 열전달 거동을 확인하였다. 또한 냉각수의 기화 현상을 방지하기 위해 발열체의 온도를 290-370 K로 바꿔 가며 열전달 거동을 확인하였다. 수치 해석결과, 5층의 열배출기가 최대 120 W/cm2 로 높은 단위면적당 열배출량을 가지는 것을 확인하였으나, 열배출기 전체의 열배출량을 기준으로하는 열배출효율은 0.6 정도로 낮은 효율을 가짐을 확인하였다. 반면에 3층의 열배출기의 경우, 열배출 효율이 0.8에 달하며, 2층의 열배출기 보다 열배출 효율이 좋다는 것을 확인할 수 있었다.

• Journal of Korea Water Resources Association
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• v.37 no.4
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• pp.329-339
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• 2004

The main objective of this study is to develop a GIS-based two-dimensional model for the simulation of rainfall-runoff process and overland flow of a watershed. The tasks of this study are summarized: to develop a two-dimensional model for overland flow and to construct a rainfall-runoff simulation system linked with GIS. The mathematical formulation of the model incorporates four parts: spatially varied rainfall, spatially distributed infiltration, 1-directional, 4-directional and 8-directional overland flow routing scheme, and one-dimensional channel routing scheme. For the development of stochastic model, Monte Carlo simulation method has been directly integrated into the model. GIS using Arc/Info and ArcView has been applied to prepare the model input data(elevation, soil type, rainfall data, etc.) for a simulation and to demonstrate the simulation results.

• Journal of Korea Water Resources Association
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• v.57 no.4
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• pp.263-276
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• 2024

Since the first introduction of one-dimensional transient storage modeling in the field of solute transport analysis in rivers, its application has notably expanded for various purposes, including for hydrology and geobiology over the past few decades. Despite strides in refining transient storage models, there remain unresolved challenges in simplifying complex river transport dynamics into concise formulas and a limited set of parameters. This review paper is dedicated to cataloging and assessing existing transient storage models, outlining the difficulties associated with model structures, parameters, and data, and suggesting directions for future research. We seek to enhance understanding of transient storage by highlighting the importance of continuously evaluating residence time distribution modeling, integrating hydrodynamic models, and using data with minimal assumptions. This paper would contribute to advance our comprehension of the transient storage process, offering insights into sophisticated modeling techniques, pinpointing uncertainty in parameters, and suggesting the necessary avenues for further study.

• Economic and Environmental Geology
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• v.28 no.4
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• pp.327-335
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• 1995

Illite/smectite (I/S) in the Beaufort-Mackenzie Basin, Arctic Canada has been scrutinized on the basis of mineralogical analysis of 215 core and drill-cutting samples from 22 exploratory wells onshore and offshore. I/S in the Beaufort-Mackenzie Basin includes the following four types: random, a mixture of random and ordered, R1-ordered, and R>1-ordered I/S. A mixture of random and ordered I/S occurs in the transitional interval between random and R>1-ordered I/S, and may represent a metastable state in the ordering reaction. A widespread occurrence of the mixture in natural environments suggests that the ordering reaction may be a slow process that results in co-existence of reactants and products. K-saturation experiments show that layer charges of expandable layers in I/S are variable. High-charge expandable layers transform into illite-like layers upon simple K-saturation. K-saturation alters the composition and/or the degree of ordering in I/S, suggesting that illitization in nature can be transformational.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.108-108
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• 2019

낙동강에는 2010-2012년 4대강 사업 완료 후 8개의 다기능 보가 설치되었다. 보 설치로 인해 물의 체류시간이 증가하고 보 상류에는 정체수역이 광범위하게 형성되었다. 이후 지속된 가뭄과 여름철 고온현상이 겹치면서 남조류의 과잉성장(녹조현상)이 빈번히 발생하여 수생태계 건강성에 문제를 초래하는 등 사회적 이슈로 자리잡게 되었다. 조류의 과잉성장을 해결하기 위해 정부에서는 총인(TP) 방류수 수질기준 강화, 펄스형 방류기법 운영 등 대책을 추진하였으며, 녹조 우심지역을 선정하고 지역 특성에 맞는 대응방안을 수립하여 추진하고 있으나, 그 효과가 국부적이고 일시적이어서 근원적 대책 마련이 필요한 실정이다. 일반적으로 남조류의 과잉성장에 영향을 미치는 요소는 높은 영양염류(질소, 인)와 유기물 농도, 고온과 안정적인 성층강도, 그리고 남조류의 생리적 특성 등으로 매우 다양하기 때문에 정확한 발생 원인의 분석이 어려운 경우가 많다. 그러나, 보에 의해 흐름이 조절되는 하천에서는 유량, 유속 및 수온성층 등이 남조류 성장과 천이특성에 가장 민감한 영향을 미친다. 선행 연구사례에서는 유량과 남조류 생체량이 서로 반비례 관계를 가진다는 점과 상 하층간의 온도차(수온성층)가 남조류 우점과 밀접한 관련이 있다는 것을 보였다(Sherman et al. 1998). 따라서 최근 국내에서도 보의 관리수위를 낮추어 유속을 증가시키고 체류시간을 감소시켜 녹조문제를 완화하려는 노력이 추진 중이다. 하지만 하천의 수질은 물리적, 화학적, 생물학적 요인들의 복잡한 상호작용의 결과이므로, 단기간의 측정 결과로 보 수위 저하의 효과를 평가하는데 어려움이 있다. 따라서 이를 과학적으로 평가하기 위해서 수리 수질 생태의 연동해석이 가능한 수치모델을 활용할 필요가 있다. 수치모델은 매개변수를 충분히 보정한다면, 다른 모든 요인은 동일한 조건에서 보 수위 저하만의 영향을 예측하는데 활용가능하다. 본 연구의 목적은 낙동강 수계 중류에 위치한 칠곡보-강정고령보 구간을 대상으로 3차원 수리 수질모델인 EFDC를 구축하고, 실측 자료를 이용하여 모델을 보정한 후 보 관리수위의 저하운영 시나리오에 따른 수질과 남조류의 시 공간적 변동 특성을 분석하는데 있다.

• Economic and Environmental Geology
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• v.45 no.2
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• pp.157-167
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• 2012

This study aimed to interpret the provenance and firing temperature of pottery from Chipyeongdong site in Gwangju, Korea though mineralogical and geochemical methods and also investigated the post-depositional alteration of pottery in burial environments. It is also presumed that they were made of soils near the site because they have similar mineralogical composition and same geochemical evolution path. Based on the results of mineralogical analysis, the pottery samples are largely divided into 2 groups; $700^{\circ}C$ to $1,000^{\circ}C$ and 1,000 to $1,100^{\circ}C$. At some pottery fired at over $1,000^{\circ}C$, it is thought that the refinement of raw materials were processed to remove macrocrystalline fragments. However, it was found that phosphate in soil environments formed amorphous aggregates with Al and Fe within the pores and voids on pottery fired at the low temperature. It indicates the contamination of pottery after burial.

• Journal of the Korean Geotechnical Society
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• v.24 no.9
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• pp.5-11
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• 2008

Seepage induced earthern slope failures occurs in concert with meteorological events when large quantities of groundwater are channeled into slopes through infiltration. The presence of flowing groundwater in earthern slopes can induce ground failures that result in significant property damage and potential loss of life. Seepage induced earthen slope failures represent a serious problem in geotechnical engineering. This research applies existing fluid-solid numerical modeling capabilities to the study and prediction of seepage induced earthen slope failures. Study of the targeted application holds potential for much needed advances in geotechnical engineering analysis technology which could be used to design more effective engineering slope stabilization interventions.

• Polymer(Korea)
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• v.29 no.6
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• pp.549-556
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• 2005

Effects of the dimensionless variables on the heat transport phenomena in the extrusion process of a single screw extruder have been studied numerically. Based on the understanding of the solids conveying related to the geometrical structure and characteristics of the screw, the heat balance equation for the solids conveying zone was established and normalized. The finite volume method and power-law scheme were applied to derive a discretized equation and the equation was solved using the alternating direction iterative method with relaxation. Effects of the dimensionless parameters, Biot and Peclet numbers, that define the heat transfer characteristics of the solids conveying zone have been investigated with respect to the temperature of the feeding zone and the length of the solids conveying zone. As the Biot number is increased, the heat loss by cooling dominates to decrease the temperature of the barrel but it has little effects on the temperature of the solids bed and the length of the solids conveying zone. On the other hand, if the Peclet number is increased, the convection term dominates to decrease the temperature of the solids bed and it results in an increase in the length of the solids conveying zone.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.4
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• pp.903-908
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• 2015

This paper has analyzed threshold voltage shift for doping profile of asymmetric double gate(DG) MOSFET. Ion implantation is usually used in process of doping for semiconductor device and doping profile becomes Gaussian distribution. Gaussian distribution function is changed for projected range and standard projected deviation, and influenced on transport characteristics. Therefore, doping profile in channel of asymmetric DGMOSFET is affected in threshold voltage. Threshold voltage is minimum gate voltage to operate transistor, and defined as top gate voltage when drain current is $0.1{\mu}A$ per unit width. The analytical potential distribution of series form is derived from Poisson's equation to obtain threshold voltage. As a result, threshold voltage is greatly changed by doping profile in high doping range, and the shift of threshold voltage due to projected range and standard projected deviation significantly appears for bottom gate voltage in the region of high doping concentration.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.210-213
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• 2010

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intended to simulate the process of fuel vaporization. LES without chemical reaction was conducted to investigate the flow characteristics at the near-fuel surface and the behavior of turbulent structures which is evolved by the wall blowing at the Reynolds number of 23,000. Cylindrical geometry was considered to get the most reality of the calculation results because real hybrid rocket motor is circular grain configuration. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.