• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.43-50
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• 2000

In this paper, the consolidation efficiency and the equivalent diameter of the cross shaped drain are examined by using the laboratory test and the numerical model, and the results are compared with those of the band shaped drain. The equivalent diameter of the tested drains is back-calculated from the laboratory experiment and compared with those calculated from the formula suggested in the literature. The efficiency of the cross shaped drain is evaluated by using the 3-D flow program which was validated by the settlement-time test fill data. The results of laboratory test show that the equivalent diameter of the band shaped drain was close to the Rixner's formula and that of the cross shaped drain was fit to the following formula: $d_w\;=\; \\tarc{3}{4}.(b+t)$The results of the numerical analysis show that the cross shaped drain can reduce the consolidation time by 9-10% from that for the band shaped drain. The equivalent diameter obtained from the numerical flow model by using the field data is 3.5 times smaller than that obtained from the laboratory consolidation test.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.1002-1009
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• 2010

I made the axon to the electrical transmission model and then constructed electrical equivalent model using Kirhhoff's current law and voltage law in this paper. I calculated various axon parameters in order to analyze the electrical potential hehavior versus minute distance chang of axon. The transmission velocity of unmyelinated nerve is proportional to square root of axon diameter, while that of myelinated nerve is directly proportional to its diameter. Because the transmission of myelin sheath is independent of voltage unlike unmyelinated sheath, the Hodgkin-Huxley model across the membrane is not so precise.

• Journal of the Korean GEO-environmental Society
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• v.4 no.2
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• pp.27-37
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• 2003

In this research stress-strain behavior of composite geocell-soil systems under triaxial condition and the influence of strength due to the presence of geocell were studied. For the research a series of triaxial tests were carried out on sand specimens confined by flexible-walled single rubber cell. The diameter of all rubber cells placed at the center of the soil sample were 50 mm. Three rubber sizes, i.e. 35, 50 and 70 mm height, were applied to the soil specimen and the size of soil specimen was 50 mm in diameter and 100 mm in height. Three different densities of soil were used for the tests. In general, it was observed that the sand specimen develops an apparent cohesion due to the confinement by the geocell. The magnitude of this cohesion seemed to be dependent to the properties of the geocell material. The test results have shown that the geocell material for this research not only develops the apparent cohesion but also increases the angle of friction whereas geosynthetic material in the references showed only the increase of apparent cohesion. From the application of geocell-soil composites to the hyperbolic model, it was recognized that the determination of the peak strength influences the behavior of the geocell-soil composites.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.570-575
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• 2001

An experimental study is performed to investigate the characteristics of vortex shedding behind a circular cylinder with serrated fins using hot-wire anemometer. Strouhal numbers which are calculated using outer diameter of a circular cylinder with serrated fins are higher than that of a circular cylinder. Fin thickness and pitch are closely related with vortex shedding frequency and play increasing or decreasing vortex shedding after transient Reynolds numbers. Strouhal numbers using effective diameters which are proposed in this paper agree with that of a circular cylinder. After transient Reynolds number, a trend of Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.8
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• pp.1077-1086
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• 2001

An experimental study is performed to investigate the characteristics of vortex shedding behind a circular cylinder with serrated fins using hot-wire anemometer. Strouhal numbers which are calculated using outer diameter of a circular cylinder with serrated fins are higher than that of a circular cylinder. Fin thickness and pitch are closely related with vortex shedding frequency and play increasing or decreasing vortex shedding after transient Reynolds number. Strouhal numbers using effective diameters which are proposed in this paper agree with that of a circular cylinder. After transient Reynolds number, a trend of Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter.

• Journal of the Korean Solar Energy Society
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• v.29 no.3
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• pp.73-82
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• 2009

포화상태 핵비등과 저 Re수의 흐름비등에서 얻어진 실험결과를 바탕으로 하여, 기포가 성장하는 동안의 등가 기포 직경과 열전단율의 거동에 대한 기포 형상 가정의 효과를 제시하기 위한 해석적인 연구를 수행하였다. 이러한 목적을 달성하기 위하여, 등가 기포 반경이 기포가 성장하는 동안 촬영된 기포의 이미지로부터 얻어질 수 있는 형상 가정을 이용하여 계산되었다. 그리고 열전달율을 포화상태 핵비등 동안 미세크기의 히터와 휘스톤브리지 회로를 이용하여 측정하였다. 그리고, 기포 형상 가정의 효과를 실험결과와 비교하였고, 이를 통해 단일 기포의 성장 거동을 분석하기 위한 기포 형상 가정이 매우 중요함을 보였다.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.27-30
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• 2002

An experimental study is performed to investigate the characteristics of near wake behind a circular cylinder with serrated fins using the constant temperature anemometer and through flow visualization. Previous report(Boo at al., 2001) shows that there are three different modes in vortex shedding behavior. This paper is focused on the identification of the physical reasons why the difference is occured in vortex shedding. The through flow velocity crossing fins decreases as increasing fin height and decreasing fin pitch mainly due to the flow resistence. Vortex shedding is affected strongly by velocity distribution around fin tube, especially by the velocity gradient. The velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. Those differences in velocity gradients generate different vortex shedding mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1191-1200
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• 2002

The measurements of velocity vectors are made in the near wake(X/d=5.0) of a circular cylinder with serrated fins. Velocity of fluid which flow through fins decreases as increasing fin height and freestream velocity and decreasing fin pitch. Therefore the velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. The discontinuity of the streamwise velocity gradient is observed near the fin edge and causes significant changes in V-component velocity distribution in the near wake. This change attributes to the differences in Strouhal number and entraintment flow behavior. Increased turbulent intensity around a circular cylinder due to the serrated fins and entrainment flow are important factors for the recovery of velocity defect. The widths of velocity and turbulent intensity distribution of fin tubes are wider than those of a circular cylinder. The normalized velocity and turbulent intensity distributions with a hydraulic diameter which is proposed in this paper are in closer agreement with those of a circular cylinder.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.31-37
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• 2010

Shape conversion coefficient and equivalent diameter for changing 2D image to 3D image by the Digital Image Process(DIP) have been suggested and modified particle size distribution curve has been showed. Couple of aggregates, like two different marine aggregates and two different crushed stones, have been employed. The measured flatness ratios of each aggregate were 0.30, 0.36, 0.47 and 0.83, respectively. Also, the conversion shape coefficients of each aggregate were determinded as 0.77, 0.78, 0.84 and 0.92. The size of aggregate has been modified by multiplying the shape conversion coefficient and the aggregate size from DIP. The modified gradation curve with modified volume and weight of aggregate has been suggested. Within the limited test results, DIP is one of useful to get the particle shape of aggregate with limitation of measuring errors and to apply the particle distribution curve.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.419-427
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• 2017

In mountainous rivers, the drag force acting on cobbles abundant in the riverbed surface is important in predicting behavior and response of the river. However there is little research for the drag coefficients of cobbles. This paper is to carry out the experiments for drag force of cobble and analyze the relation between the cobble shape and the drag coefficient. The effects of the shape factor on the drag coefficients $C_D$ when the long axis or the short axis of the cobbles are parallel to the direction of flow velocity were analyzed. The coefficient of drag force increased with the nominal diameter Reynolds number $R_{ep}$. The drag coefficients are greater in short axis than long axis. The coefficient of determination of the relation between $C_D$ and $R_{ep}$ is greater in long axis than short axis. This means that the drag forces acting on the irregularly-shaped cobbles depend on the axis. A change of the drag force distribution has brought about the alternative swing of cobbles. For $R_{ep}$ > 12,000, the amplitude of the swing has been increased sharply and especially was greater in short axis than long axis.