• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.271-278
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• 2004

Numerical analysis of wind effects on civil engineering structures was performed. Aerodynamic effect often becomes a governing factor and aeroelastic stability boundary becomes a prime criterion which should be confirmed during the structural design stage of bridges because the long-span suspension bridges are prone to the aeroelastic instabilities caused by wind. If the wind velocity exceeds the critical velocity that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. Navier-Stokes equations were used for the aeroelastic analysis of bridge girder section. The aeroelastic simulation is carried out to study the aeroelastic stability of bridges using both Computational Fluid Dynamic (CFD) and Computational Structural Dynamic (CSD) schemes. Critical flutter velocities were computed for bridges with different stiffness. It was confirmed that the critical flutter velocity of bridge girder section was sensitive to the change of structural stiffness.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.202.1-202.1
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• 2014

최근 대용량 에너지 저장장치로 사용하고자 하는 리튬-공기전지는 리튬 음극과 액체 전해질 사이의 화학적 불안정성이 문제가 되고 있다. 또한 리튬이온전지는 액체전해질의 사용으로 인해 폭발 등의 안정성 문제가 대두되고 있는 실정이다. 때문에 리튬-공기전지에서 리튬 음극을 액체 전해질로부터 보호할 수 있으며, 리튬이온전지의 액체전해질과 대체하였을 때 전극과도 안정한 고체전해질의 연구가 필요하다. 고체전해질은 구조적으로 crystalline, glassy, 폴리머로 나눌 수 있는데, 이 중 crystalline 구조의 고체전해질은 glassy 및 폴리머 고체전해질에 비해 상온에서 비교적 이온전도도가 높다고 알려져 있다 [1]. 그러나 이온전도도가 높은 황화물 및 질화물 고체전해질은 수분에 민감한 반면 [2,3], 산화물 계열의 물질은 안정할 것으로 예상된다. 본 연구에서는 이온전도도가 높은 산화물인 lithium lanthanum titanate ($Li_{0.5}La_{0.5}TiO_3$, LLTO)를 고체전해질로 선정하여 다양한 환경에서 화학적 안정성에 관해 연구하였다. LLTO와 각종 용액과의 화학적 안정성을 살펴보기 위해 고체전해질을 DI water, 1 M $LiPF_6$ Ethylene Carbonate (EC)-Dimethyl Carbonate (DMC) (50:50 vol.%), 0.57 M LiOH (pH=13), 0.1 M HCl (pH=1)에 immersion하고 무게, 표면형상, 상(phase), 이온전도도 등의 변화를 관찰하였다. 또한 LLTO와 전극간의 반응성을 알아보기 위해 LLTO 분말과 음극물질인 $Li_4Ti_5O_{12}$ 및 양극물질인 $LiCoO_2$ 분말을 혼합한 후 $300^{\circ}C{\sim}700^{\circ}C$의 온도범위에서 열처리하여 반응을 가속화 한 후 상변화 현상을 살펴보았다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.4
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• pp.165-171
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• 2018

In this study, the shape of the flow control structure within a DVR was designed for heat dissipation of the CPU. The proposed design consists of three thin metal plates, which directly controls the air flow inside the DVR box and forces the air to pass through the CPU, thereby efficiently dissipating heat from the CPU. The shape of the structure was determined using parametric studies. To verify the design result, we carried out a three-dimensional time dependent numerical analysis using a commercial fluid dynamics analysis package FlowVision. As a result of experiments with a real DVR equipment, it is confirmed that the temperature of the CPU is significantly reduced compared to the initial model.

• Journal of the Korea Concrete Institute
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• v.13 no.4
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• pp.397-405
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• 2001

In clod weather regions, a strong seasonal wind brings sea salts to the land. In addition to it, recently, the spreading amount of deicing salts has increased numerously for purpose of removing snow and ice. Thus the salts environment around concrete structures becomes so severe that various damages of concrete due to applied salts will be brought up. Much of countries such as America, Europe etc. is carried out study for effects of deicing salts on concrete. However, there are not test methods for deterioration of concrete subjected to both freezing-thawing and chloride in Korea. In this study, we carried out test for the compound deterioration subjected to both freezing-thawing and chloride attack, to investigate the effects of sodium chloride on the deterioration of concrete. The test was performed to investigate the effects of cement type, strength and air content on the scaling deterioration of concrete. As a result, the scaling deterioration was accelerated in the presence of salts. And the resistance to scaling was strongly influenced by the type of cement, the strength and air content of concrete.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.02a
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• pp.29-48
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• 2001

일반적인 폐수처리 시 여러 광물들이 사용되는 데 예를 들면, 수산화칼슘 및 탄산나트륨은 중화제, 점토는 응집제, 알룸(alum) 및 염화철은 인 제거제로 사용되고 있다. 산성광산배수인 경우에는 알칼리성의 중화제로 석회 (CaO), 석회석 (CaCO$_3$), 가성소다 (NaOH), 탄산나트륨 (NaCO$_3$) 등이 사용된다. 그러나, 설비비 및 유지비가 많이 들어 몇 십년 동안 계속해서 침출되는 산성광산배수를 처리하기에는 문제가 있다. 산성광산배수 (Acid Mine Drainage, AMD)는 pH가 6.0 미만이고 총산도 (totalacidity)가 총알카리도 (total alkalinity)를 초과하는 물로서 노천광이 가행되었던 지역, 가행중이거나 휴광 또는 폐광된 광산에서 유출된다. 또한 도로사면 절개부나 지하철 터널에서도 황철석(pyrite)이나 백철석 (marcasite)을 함유하는 층이 공기 중에 노출되면 산성수가 침출되어 나오기도 한다. 산성광산배수에 의한 하천수의 오염이 매우 극심하여 때로는 미생물마저도 그 속에 살 수 없게 된다. 산성광산배수에 의해 오염된 하천수의 오염범위는 산성수의 양, 농도, 하천에 유입되는 산성수의 분포, 상류에서 흘러드는 오염되지 않은 물의 양, 지류에서 유입되는 물의 양에 따라 좌우된다. 산성광산배수 오염이 문제시되고 있는 나라는 미국을 포함하여 호주, 일본, 한국, 러시아, 남아연방 등이다. 산성광산배수는 환원환경에서 생성된 석탄층 및 접촉교대 또는 열수에 의해 생성된 금속광이 공기 및 물에 노출되어 생성되는 자연적인 현상이다. 그러나 국지적인 지역에서 인간이 이 광상들을 환경영향을 고려하지 않고 대규모로 개발할 때 인간 생활에 심각한 영향을 미치는 것이다. 광산산성배수를 처리하기 위해 상기와 같이 여러 기술이 도입 적용되었으며 일부 기술들은 현재도 사용되고 있다. 각 기술마다 일장일단이 있으므로 경비의 과다, 유지 및 관리에 대한 지속성 여부, 공간의 확보 여부, 지역적 특수성에 맞춰 가장 적합한 방법을 채택하여야 하며 꾸준히 채택한 기술의 개량 및 새로운 기술의 첨가가 요구되고 있다. 따라서, 산성광산배수 오염지대에 대해 획일적으로 같은 처리방법을 채택하여 사용하는 것보다 각 지역 또는 광산산성폐수가 유출되어 나오는 광산폐기물의 특성 등을 고려하여 거기에 맞는 기술들을 복합적으로 또는 단독으로 사용하되 처리방법 채택 시 신중을 기할 것이 요망된다.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2004.11a
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• pp.250-255
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• 2004

To analyze delay, Seoul - Daegu line of Korea High Speed Railway was divided into three sections and analyzed independently by the business characteristics. The analysis on the project delay reasons was performed on macro and micro scales. This analytic method was named as 'Macro-Micro Delay Analysis Method (MMDAM)'. The macro scale analysis has three approaches, which are (1) scheduling, (3) structural characteristic, (3) and responsibility of project administrative works. Micro analysis also has three, methodologies which are (1) As Planned Method, (2) As Built method, (3) Modified Time Impact Analysis for analyzing the most influential section which the largest delay occurred. Using elicited project delay reasons from above analysis, the questionnaire was carried out for analyzing the influence of project delay reason. The reasons of the delay were driven from two different aspects (1) structural characteristic and (2) responsibility of the people involved in the project. The reasons that were identified from aforementioned three sections are the factors of the delay of the large-scale government driven projects. Finally, the author suggested the methodology of identifying the project delaying factors. The author also analyzed delay reasons in both the overseas and domestic cases of high rapid railway construction and has elicited some benchmarks for the future projects.

• The Korean Journal of Petroleum Geology
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• v.13 no.1
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• pp.24-29
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• 2007

The main purpose of this study is to identify the shallow gas origin in the KSSM zone. Based on the results of gas composition and isotope in the headsapace gas, the shallow gas is mainly composed of methane and carbon and deuterium isotopes (${\delta}^{13}CCH_4$ and ${\delta}DCH_4$) of methane has ranged from -93.4%o to -70.9%, and from -228%o to -199%o in each. These results imply that shallow gas has predominately biogenic source by $CO_2$ reduction rather than thermogenic. The carbon isotopic separation (${\varepsilon}_c$) between methane and carbon dioxide $(CO_2)$ has a range of 54.4 to 72.2, it also supports biogenic origin of shallow gas.

• Korean Journal of Ichthyology
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• v.23 no.1
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• pp.70-74
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• 2011

During the winter, the rice field-dwelling muddy loach Misgurnus mizolepis is buried in burrows constructed of mud and are subjected to exposure to air at times of shortage of water. To investigate the environmental factors that lead to changes of the skin mucus cells of the muddy loach in rice fields, we carried out an experiment where we artificially exposure the fish to air, duplicating as close as possible winter conditions in nature. During the summer, a water tank containing M. mizolepis was filled with mud, and the water was allowed to evaporate. After a month of evaporation, the loach constructed burrows similar to those in a winter rice field. The epidermis in the experimental fish was mostly occupied by large elongated mucus cells, whose numbers drastically increased in all observed regions of the dorsum, lateral region, and the occiput. Such features are typically seen in fishes in wild habitats during the winter season.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.235-240
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• 2010

Transpiration cooling is the most effective cooling technique for liquid rocket and air-breathing engines operating in aggressive environments with higher pressures and temperatures. Combustor liners and turbine vanes are cooled by the coolant(air or fuel) passing through their porous walls and also the exit coolant acting as an insulating film. However, its practical implementation has been hampered by the limitations of available porous materials. The search for more practical methods of increasing the internal heat transfer within the walls has led to the development of multi-laminate porous structures, such as Lamilloy$^{(R)}$ and Transply$^{(R)}$. This paper reviews recent research activities of transpiration cooling for the propulsions of liquid rocket, gas turbine, and scramjet.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.55-65
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• 2006

The air and water flow distribution are experimentally studied for a round header - flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is thirty. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.