• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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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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• v.38 no.4
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.116-122
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• 1988

Interfacial shear stresses have been determined for countercurrent stratified flow of air and water in a nearly-horizontal rectangular channel, based upon measurements of pressure drop, gas velocity profiles and mean film thickness. A dimensionless correlation for the interfacial friction factor has been developed as a function of the gas and liquid Reynolds numbers. Equivalent surface roughnesses for the interfacial friction factor have been calculated using the Nikuradse correlation and have been compared with the intensity of the wave height fluctuation on the interface. The results show that the interfacial shear stress is mainly affected by turbulent mixing near the interface due to the wave motion rather than by the roughened surface.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.875-886
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• 1994

This study is to develop an advanced storm runoff analysis program which takes geomorphological characteristics of watershed into consideration in determining model parameters. Basic concept of storm runoff modelling is based upon the kinematic wave theory. And numerical solution is obtained by the characteristic curve method. The storm runoff analysis program developed by this study is composed of multiple equivalent roughness sub-basins, each of which has two equivalent catchments on both side of a stream. Because it is based upon the stream-order of the Strahler system, the equivalent catchment-stream network reflects the stochastic geomorphological characteristics in the model parameter. Applicability and reliability of the storm runoff analysis program is evidenced by model calibration and verification process utilizing geographical and hydrological data of the Bocheong-river area which is a representative watershed of IHP projects in Korea. This study will hopefully contribute to hydrological calculation essentially required to understand water quality effect caused by regional development.

• Journal of Environmental Science International
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• v.20 no.7
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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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• v.24 no.2
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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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• v.5 no.2_3_4
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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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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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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• v.29 no.4
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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.

• Journal of Korean Society of Water and Wastewater
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• v.13 no.2
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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.