• 대한기계학회논문집B
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• 제36권5호
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• pp.477-485
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• 2012

수평 덕트 내 임계점부근의 유체 유동 및 열전달특성은 중력과 함께 임계영역에서의 열역학 및 전달 물성치의 많은 변화와 직접적으로 연관되어 있다. 본 연구에서는 수평 직사각 덕트 내 임계점부근의 물에 대한 대류열전달특성을 전산해석을 통하여 분석하였다. 이를 통해 국부적인 열전달계수와 유속, 온도, 그리고 물성치분포를 포함한 대류열전달특성에 대해 임계점 근접효과와 함께 비교하였다. 벽으로부터의 열전달에 따른 유체 밀도감소로 덕트 내 유동방향으로의 유속증가와 함께 유체가 액체에서 기체 같은 상태로 천이하는 형태의 유동장특성을 보여준다. 덕트의 윗면, 옆면, 그리고 아래면 각각의 국부적인 열전달계수분포에 큰 차이가 있으며 준임계점 온도부근에서 난류전달특성의 향상으로 열전달계수의 최대치에 이르게 된다. Nu 수는 덕트 내 압력과 종횡비에 영향을 받으며 임계압에 가까워질수록 최대 Nu 수는 급격히 증가하게 된다. 이와 함께 기존의 열전달상관식을 통한 결과와 예측된 Nu 수 분포를 비교하였다.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제1권2호
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• pp.105-117
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• 1997

The formation mechanism of the vortex streets in the lee of the mountain is investigated by a three-dimensional numerical model. The model is based upon the hydrostatic Boussinesq equations in which the vertical turbulent momentum flux is estimated by a turbulence parameterization scheme, but the horizontal viscosity is assumed to be constant. The results show that Karman vortex streets can form even without surface friction in a constant ambient flow with uniform stratification. The vortex formation is related to breaking of the mountain wave, which depends on the Froude number (Fr). In the case of a three-dimensional bell-shaped mountain, the wave breaking occurs when Fr is less than about 0.8, while a Karman vortex forms when Fr is less than about 0.22. Vortex formation also depends on Reynolds number, which is estimated from the horizontal diffusivity. The vortex formation can be explained by the wave saturation theory given by Lindzen (1981) with some modification. Simulations in this study show that in the case of Karman vortex formation the momentum flux in the lower level is much larger than the saturated momentum flux whereas it is almost equal to the saturated momentum at the upper levels as expected from the saturation theory. As a result, large flux divergence is produced in the lower layer, the mean flow is decelerated behind the mountain, and the horizontal wind shear forms between unmodified ambient wind. The momentum exchange between the mean flow and the mountain wave is produced by the turbulence within a breaking wave. From the result, well developed vortices like Karman vortex can be formed. The results of the momentum budget calculated by the hydrostatic model are almost the same as nonhydrostatic results as long as horizontal scale of the mountain is 10 km. A well developed Karman vortex similar to the hydrostatic one was simulated in the nonhydrostatic case. Therefore, we conclude that the hydrostatic assumption is adequate to investigate the origin of the Karman vortex from the viewpoint of wave breaking.

• Nuclear Engineering and Technology
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• 제24권2호
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• pp.130-140
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• 1992

동방향 성층이상유동에서의 직접적촉 응축현상을 일차원 모델인 RELAP5/MOD2와 /MOD3를 이용하여 해석하였으며, 해석결과를 Northwestern의 실험결과와 비교·검토하였다. 해석결과 RELAP5의 공유열전달 모델은 동방향 성층이상유동에서 응축율을 비교적 잘 예측하고 있다. 그러나 공유접촉면에 파형이 생기는 경우는 물경계두께 및 국부 열전달계수는 유사한 범위로 일치할분 현상을 예측하는데 상당한 차이가 있다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.840-851
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• 2010

This study analyzed data on the pore water pressure, the ground water level, the horizontal displacement and the resistivity monitoring from instrument system, which is established to evaluate the safety in reservoirs. The pore water pressure in the embankment ranged from $0.035{\sim}1.116kg/cm^2$. The seepage that piping showed, as well as the leakage from the reservoirs are acceptable for the safety management of the reservoir. The maximum horizontal displacement and direction analyzed from the measured inclinometer data gives us very effective information to evaluate the safety in reservoirs. The resistivity monitoring technique, which is obtained on the reservoir crest, is an efficient tool to detect leakage zone. The safety index(SI) was predicted by the resistivity monitoring, and was evaluated to have a safety level of 0.8-1.0 at all reservoirs. Safety evaluations of reservoir through instrument systems are effective when studying the embankment, when the results of the instrument system have been analyzed compositively.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.563-570
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• 2001

In this study, the charactersistics of horizontal drains used to stabilize the dredged fill are investigated experimentally by doing tensile strength test, discharge capacity test, and filter clogging test. The types of the drains selected for the study are filament type (Tyre-E), embossed type(Type-P) and heat bonded cubic type with the thickness 10mm(Type-010) and 5mm(Type-05). The results of tensile strength and discharge capacity test show that the performance of drain Type-O10 was better than the other drains. This is caused by the fact that the lattice shape core of drain Type-O10 has strong rigidity and minimizes the loss of the sectional area of discharge with increased confining pressure. Analyzing the compatibility of filters by the results of the strength characteristics test and clogging test, the filter of filament type drain produced with polyester clothed polyamide performed well.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.413-416
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• 2009

Since the solar radiation is main input for sizing any solar photovoltaic system and solar thermal power system, it will be necessary to understand and evaluate the insolation data. The Korea Institute of Energy Research(KIER) has begun collecting horizontal global insolation data since May, 1982 and direct normal insolation data since December 1992 at 16 different locations. Because of a poor reliability of existing data, KIER's new data will be extensively used by solar energy system users as well as by research institutes. Among some significant results, the yearly averaged horizontal global insolation was turned out 3.61 kWh/$m^2$/day and the yearly mean 5.38 kWh/$m^2$/day of the direct normal insolation was evaluated for clear days.

• 한국수학교육학회지시리즈E:수학교육논문집
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• 제29권2호
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• pp.241-254
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• 2015

기하학적 튜브디자인을 통한 아르키메데스별 창작과 관련된 체계적인 연구개발이, 최근 수년간 브리지컨퍼런스 수학예술 갤러리에 선정된 모델을 중심으로, 진행되어 왔다. 본 연구는 창의적 실험수학교육에 유용한 소스로, 아르키메데스 별 창작활동에 관한 이론적 배경 그리고 아르키메데스 수평별 체계적인 분류 및 그에 따른 시작단계 수준의 개발 성과를 소개한다.

• 한국태양에너지학회 논문집
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• 제29권4호
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• pp.15-21
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• 2009

Since the solar radiation is main input for sizing any solar photovoltaic system and solar thermal power system, it will be necessary to understand and evaluate the insolation data. The Korea Institute of Energy Research(KIER) has begun collecting horizontal global insolation data since May, 1982 and direct normal insolation data since December 1992 at 16 different locations. Because of a poor reliability of existing data, KIER's new data will be extensively used by solar energy system users as well as by research institutes. Among some significant results, the yearly averaged horizontal global insolation was turned out 3.60 kWh/$m^2$/day and the yearly mean 2.62 kWh/$m^2$/day of the direct normal insolation was evaluated for all days.

• Geomechanics and Engineering
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• 제10권5호
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• pp.565-575
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• 2016

Geosynthetics reinforced soil (GRS) walls constructed on weak grounds may change in both the horizontal earth pressure and deformation on wall facing. However, only few studies were done in the literature to measure and analyze the horizontal external deformation behavior of GRS walls constructed on soft grounds for a long period of time. The present study describes the external deformation behavior of GRS walls observed for 12-year long-term performance. The horizontal deformation of the geosynthetics-wrapped-facing GRS walls shows a passive behavior along one third of the wall height, from top going downwards, and active behavior for the rest of the wall height. Even if the geogrid and nonwoven geotextiles are exposed directly to sunlight and rainfalls in a span of 12 years, they have functioned well as wall facing. Therefore, the geosynthetic reinforcement material is strong enough to resist ultraviolet rays.

• 대한기계학회논문집B
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• 제24권7호
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• pp.930-937
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• 2000

A series of data sets for the heat transfer coefficient versus wall superheat has been obtained experimentally using various combinations of tube diameters ($9.7{\sim}25.5mm$), surface roughness ($15.1{\sim}60.9nm$), and tube orientations (horizontal and vertical) to obtain effects of tube diameters on nucleate pool boiling heat transfer for the saturated water at atmospheric pressure. In addition, the results are compared with the well known Cornwell and Houston's correlation for horizontal tubes to identify the deviation of the present experimental data from the correlation and the applicability of it to vertical tubes. The experimental results show that the heat transfer coefficient decreases as the tube diameter increases for both horizontal and vertical tubes and they are in good agreement with the Cornwell and Houston's correlation within ${\pm}20%$ scatter range.