• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.247-254
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• 2000

In this study, the reinforcing effect of micropile for weathered rock is analysed by laboratory model tests. Especially, the effect of the number, the surface roughness, and length of micropile are focused. The results of tests are as follows: $\circled1$ The deformation modulus of reinforced ground is less than equivalent deformation modulus, and $\circled2$ Increasing effect of unconfined compressive strength is not large as times as increasing the number of micropile.

• Structural Engineering and Mechanics
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• 제38권4호
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• pp.443-457
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• 2011

The loss of strength in a structure as a result of cyclic loads over a period of life time is an important phenomenon for the life-cycle analysis. Service loads are accentuated at the areas of stress concentration, mainly at the connection of components. Structural components unavoidably are affected by defects such as surface scratches, surface roughness and weld defects of random sizes, which usually occur during the manufacturing and handling process. These defects are shown to have an important effect on the fatigue life of the structural components by promoting crack initiation sites. The value of equivalent initial flaw size (EIFS) is calculated by using the back extrapolation technique and the Paris law of fatigue crack growth from results of fatigue tests. We try to analyze the effect of EIFS distribution in a multiple site damage (MSD) specimen by using the extended finite element method (XFEM). For the analysis, fatigue tests were conducted on the centrally-cracked specimens and MSD specimens.

• 대한기계학회논문집
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• 제12권1호
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• pp.116-122
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• 1988

본 연구에서는 공기와 물을 매질로 사용하여 3차원 계면파가 존재하는 근사수평 반류성층유동에서의 계면전단응력과 마찰계수를 결정하였다. 기상과 액상의 유량조건에 따라 3차원 계면파의 특성을 needle contact법에 의하여 측정 하였으며, 기상의 압력강하와 속도분포를 구하여 계면전단응력을 구하였다. 또 공학적인 응용을 위하여 3차원과 영역에서의 계면마찰계수에 관한 실험식을 개발하였다. 그리고 거칠은 고체표면에서의 마찰계수를 표현한 Nikuradse식을 이용하여 계면의 등가조도(equivalent roughness)를 계산하였으며 이것을 계면의 파고교란강도와 비교분석하여 계면전단응력에 영향을 미치는 인자들을 규명하였다.

• 대한토목학회논문집
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• 제14권4호
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• pp.875-886
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• 1994

본 연구는 유역의 지형인자를 고려한 강우의 수리학적 단기유출 해석 시스템을 개발한 것이다. 강우 유출의 기본 개념은 Kinematic Wave 이론에 의거하였으며, 그 수치해는 특성곡선 추적법에 의하여 산출된다. 개발된 강우유출해석 시스템은 한개의 하도를 중심으로 좌우 2개의 등가사면을 지니는 단위 등가조도 모델이 복수개의 하도망을 따라 결합된 복합 등가조도 유역 모델로 구성되며, 등가조도유역 모델은 유역의 하천차수이론에 근거하여 규정됨으로써 유역이 지니는 확률적 지형인자를 모델 파라메타에 함축시키는 특성을 지닌다. 모델 파라메타의 민감도분석과 IHP 대표유역인 보청천 유역의 지형 및 수문자료를 이용한 모델 보정과 검정을 통하여 제안 시스템의 현장 적용성과 재현가능성이 확인되었다. 본 연구의 성과에 의하여 해석대상 등가유역의 시공간상 임의 위치에서 수리량의 시간변동 예측 및 유역의 개발에 따른 단기적 수질변동 해석에 요구되는 수리량의 해석이 가능하게 되었다.

• 한국환경과학회지
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• 제20권7호
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• pp.839-843
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• 2011

We have established a wind map of Singapore, a city-state characterized its land cover by urban buildings to confirm a possibility of wind farm development. As a simple but useful approximation of urban canopy, a zero-plane displacement concept was employed. The territory is divided into 15 sectors having similar urban building layouts, and zero-plane displacement, equivalent roughness height at each sector was calculated to setup a terrain boundary condition. Annual mean wind speed and mean wind power density map were drawn by a CFD micrositing model, WindSim where Changi International Airport wind data was used as an in-situ measurement. Unfortunately, predicted wind power density does not exceed 80 $W/m^2$ at 50 m above ground level which would not sufficient for wind power generation. However, the established Singapore wind map is expected to be applied for wind environment assessment and urban planning purpose.

• Journal of Advanced Marine Engineering and Technology
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• 제24권2호
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• pp.17-23
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• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent flow in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness pitch ratio(P/e) of 4, 8 and 16 on the one side wall only. The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70,000 to 10,000. The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement, measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion, namely, the fin effect. And the results were compared with those of previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• Wind and Structures
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• 제5권2_3_4호
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• pp.347-358
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• 2002

Mean surface pressures and overall wind loads on hemispherical domes immersed in a boundary layer were obtained by numerical simulation. The effects of alternative turbulence models, Reynolds Number and surface roughness were examined and compared with earlier studies. Surface pressures on dual hemispherical domes were also calculated for three wind orientations ($0^{\circ}$, $45^{\circ}$, and $90^{\circ}$) to evaluate flow field interactions. Calculated values were compared to wind-tunnel measurements made in equivalent flow conditions.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.439-442
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• 2002

The interface between two different materials in the insulation systems is the weak-link in the underground power transmission systems, In this paper, Optimum conditions of the interface between Epoxy and EPDM is studied. The variation factor condition of interface is roughness of surface, spreading of oils, interfacial pressure and temperature. The breakdown times under the constant voltage below the breakdown voltage were also gained. The breakdown voltage at the after laying time equivalent to is calculated by the V-t characteristic and the inverse power law. When this is done, the characteristic life exponent n is used and the long time breakdown voltage can be evaluated.

• Tribology and Lubricants
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• 제29권4호
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• pp.242-247
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• 2013

This study aims to establish the fundamental basis for the design of materials used in high-speed trains, by using a lab-scale dynamometer to evaluate the characteristic behavior of metallic sintered friction materials in relation to the shape of graphite. The test results clearly demonstrate that when flake graphite and granular graphite are added equivalently, the average coefficient of friction is much lower, and it is less influenced by speed variation; moreover, friction wear is observed to be insignificantly low. Adding flake graphite increases the coefficient of friction, which leads to higher friction wear. In addition, the roughness of the disc surface was equivalent regardless of the shape of the graphite.

• 상하수도학회지
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• 제13권2호
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• pp.82-88
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• 1999

This study was to evaluate disinfection efficiency of chlorine and chloramine as secondary disinfectants in the distribution systems. Indicator organism, HPC in the suspended and attached were measured for copper, galvanized steel, PVC, and carbon steel pipes. For suspended microorganism, the PVC pipe was markedly dense among the assessed pipe materials. The attached microorganism was markedly equivalent roughness of pipe materials. In copper and galvanized pipes, chloramine was more effective that free chlorine to disinfect suspended microorganism in the contact time of 2 hours. The contact time for the 99% inactivation of suspended microorganism by chloramine was longer than that of free chlorine. Regardless of pipe materials, chloramine was effective on both disinfection efficiency and 99% inactivation time for attached microorganism. In conclusion, chloramine which is good disinfectant for long contact time was recommended as secondary disinfectant in distribution system.