• Journal of Biomedical Engineering Research
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• v.23 no.1
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• pp.27-32
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• 2002

The purpose of this study was to evacuate the effects of the number of tied hollow fibers in a novel membrane oxygenator that satisfied the limiting factor of minimizing the friction loss in the intravascular blood flow Pattern. The membrane oxygenator is a bundle consisted of several hundred ho1low fibers haying the outside diameter of 380 $\mu m$ and the axial jacket length of 600 mm. The eight different variation of tied hollow fibers in a bundle were designed. and the liquid flow pattern was controlled by a pump. The liquid pressure drop was measured by in vitro experiments using water and g1ycero1. Uniform blood flow pattern was observed for each number of tied hollow fibers. Pressure drop was 13-16 mmHg outside of the membrane oxygenator consisting of up to 700 ho1low fibers. More effective contact of liquid with the tied ho1low fibers was observed as a decrease in the number of the tied hollow fibers. and resulted in the enhancement of the friction tractor

• Journal of Korean Society of Environmental Engineers
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• v.27 no.5
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• pp.542-548
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• 2005

A fluidized bed reactor containing porous media has been known to be effective for nitrogen and organic matters removal in wastewater. The porous media which attached microbes plays important roles in simultaneous nitrification/denitrification (SND) due to coexistence of oxic, anaerobic and anoxic zone. For SND reaction, oxygen and organic substrates should be effectively diffused from wastewater into the intra-carrier zone. However, the overgrowth heterotrophic microbes at the surface of porous media may restrict from substrates diffusion. From these viewpoints, the existence and effect of heterotrophic bacteria at surface of porous media might be the key point for nitrogen removal. A porous media-membrane hybrid process was found to have improved nitrogen removal efficiency, due to stimulated denitrification as well as nitrification. Microelectrode studies revealed that although intra-media denitrification rate in a conventional fluidized bed was limited by organic carbon, this limitation was reduced in the hybrid process, resulting in the increased denitrification rate from 0.5 to $4.2\; mgNO_3-N/L/hr$.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.113-120
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• 2013

Graphite is commonly used as a solid lubricant leading to low friction coefficient and abrasion. In this study, wear behavior of sealing graphite(HK-6) at elevated temperature was evaluated. Reciprocating wear test was carried out as wear occurred graphite as a seal(HK-6) is positioned between the liner and driving shaft. Variables which are temperature, sliding speed and contact load are set. This study suggest optimized environment conditions through the wear properties of graphite.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.247-254
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• 2003

While the interests in the environmental problem during the construction are increasing, the use of low noise-vibration auger-drilled pilling is increasing to solve noise and vibration problem in pilling. Therefore, in Korea, SIP (Soil-Cement Injected Precast Pile) method is mainly used as auger-drilled pilling. However, there is no proper design criteria compatible with the ground condition of Korea, so which is most wanted. To improve and supplement this situation, direct shear tests for the friction between SIP pile skin interface and soil were executed on various conditions. Through the analysis of test results, skin friction characteristics of SIP were investigated thoroughly Also, hyperbolic model parameter fomulas which describe the friction behavior and the new non-linear unit skin friction capacity model with SM, SC soil were suggested.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.65-74
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• 2003

The dragload on pile groups in consolidating ground was investigated based on a numerical analysis. The case of a single pile and subsequently the response of groups were analyzed by 2D and 3D finite element studies. Conventional continuum elements and special slip elements were used in the analyses for comparison. Based on a limited parametric study, it is shown that dragload for a single pile and group effect are normally overestimated by continuum analyses, compared with the predictions by the slip analyses. The group effect was examined from the slip analysis by considering various factors such as pile configurations, surface loading, interface friction coefficient, and axial loading on piles. An examplary analysis and one previous experimental observation of dragload and group effects were back-analysed. The case histories demonstrated that the slip analysis might predict a better estimate of dragload and group effect compared to the no-slip continuum analysis.

• Journal of the Korean Geotechnical Society
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• v.32 no.5
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• pp.27-36
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• 2016

This paper presents the investigation of the major influence factors on the degree of soil plugging for open-ended piles based on the Coupled Eulerian-Lagrangian (CEL) numerical technique. The main objective of this study was to investigate the effect of soil plugging on the response of piles in various conditions. Through comparison of the results of field load tests, the CEL methodology was found to be in good agreement with the general trend observed by in situ measurement. Additionally, the parametric studies were performed by controlling the soil conditions, soil elastic moduli, end-bearing conditions and multi layers. It was found that the degree of soil plugging for sand layers was greater than that of clay layers. Also, the degree of soil plugging increased with an increase in both the soil stiffness and length of pile embedded in the bearing layer.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.439-446
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• 2008

We have developed a method to evaluate pumping rates from a system of pumping-well family. For a given system actual pumping rates depend on pump characteristics and the sum of the static head and the dynamic head. The static head is the elevation difference between the natural groundwater level and the outlet of the pipeline that connects all the wells. Major components of the dynamic head are groundwater drawdown in the well and pipeline head loss. The dynamic head and the pump characteristics depend on the pumping rates. Actual pumping rates are determined at the intersections of the system total-head curves and the pump characteristic curves. The Newton-Raphson's method is used to solve the nonlinear simultaneous equations. The method is applied to a hypothetical well family. Impacts of various design and operational parameters on the pumping rates are analyzed.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.124-124
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• 2000

다이아몬드에 버금가는 높은 경도뿐만 아니라 높은 화학적 안정성 및 열전도성 등 우수한 물리화학적 특성을 가진 입방정 질화붕소(cubic boron nitride)는 마찰.마모, 전자, 광학 등의 여러 분야에서의 산업적 응용이 크게 기대되는 재료이다. 특히 탄화물형성원소에 대해 안정하여 철계금속의 가공을 위한 공구재료로의 응용 또한 크게 기대된다. 이 때문에 각종의 PVD, CVD 공정을 이용하여 c-BN 박막의 합성에 대한 연구가 광범위하게 진행되어 많은 성공사례들이 보고되고 있다. 그러나 c-BN 박막의 유용성에도 불구하고 아직 실제적인 응용이 이루어지지 못한 것은 c-BN 박막의 증착직후 급격한 박리현상 때문이다. 본 연구에서는 평행자기장을 부가한 ME-ARE(Magnetically Enhanced Activated Reactive Evaporation)법을 이용한 c-BN 박막의 합성에서 적용한 증착공정 인자들의 변화에 따른 박리특성 고찰과 함께 다층박막화 및 제 3원소 혼입 방법을 적용하여 박리특성 향상 정도를 조사하였다. BN 박막합성은 전자총에 의해 증발된 보론과 (질소+아르곤) 플라즈마의 활성화반응증착(Activated Reactive Evaporation)에 의해 이루어졌다. 기존의 ARE 장치와 달리 열음극(got cathode)과 양극(anode) 사이에 평행자기장을 부가하여 플라즈마의 증대시켜 반응효율을 높였다. 합성실험용 모재로는 p-type으로 도핑된 (100) Si웨이퍼를 30$\times$40mmzmrl로 절단 후, 10%로 희석된 완충불산용액에 10분간 침적하여 표면의 산화층을 제거한 후 사용하였다. 박막실험실에서의 주요공정변수는 기판바이어스 전압, discharge 전류, Ar/N2가스유량비이었다. 합성된 박막의 결정성 분석을 FTIR을 이용하였으며, BN 박막의상 및 미세구조관찰을 위해 투과전자현미경(TEM;Philips EM400T) 분석을 병행하였고, 박막의 기계적 물성 평가를 위해 미소경도를 측정하였다. 박리특성의 고찰은 대기중에서의 자발적 박리가 일어나 90%이상의 박리가 진행된 시점까지의 시간을 측정하였고, 증착직후 박막의 잔류응력 변화와 연관하여 고찰해 보았다.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.709-709
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• 2012

보는 하천을 횡단하는 대표적인 수공구조물로써 수위를 유지하여 각종 용수의 취수 기능 및 주운 기능을 가지고 있다. 그러나 보를 설치할 경우 상류부의 유속이 점차 감소하여 유사 퇴적이 일어나며, 흐름 정체에 따른 수질 저하 및 수위 상승의 원인을 제공한다. 이러한 보의 단점을 개선하기 위해 래버린스 보에 대한 다양한 연구가 진행되고 있다. Hay 등(1970) 연구에 따르면 래버린스 보의 월류능력은 동일 수두 조건에서 선형 보보다 높은 특성을 가진다. 또한 Tsang(2000) 연구에 따르면 큰 유량 및 낮은 월류고 조건에서 폭기 효율이 뛰어난 것으로 나타났다. 박호상(2009) 연구에 따르면 경사형 마루 래버린스 보가 일반형 래버린스 보의 수심유지 범위보다 더 크며, 산소전달효율도 더 높은 것으로 나타났다. 그러나 기존 보에서 발생되는 유사퇴적 및 흐름정체 등의 문제는 여전히 존재하였다. 이와 관련하여 본 연구에서는 유사의 연속성을 유지하고 흐름의 정체를 해소하는 퇴적방지 구조를 구비한 래버린스 보(현대건설, 2011)를 제안하였다(그림 1, 2 참조). 본 연구에서는 퇴적방지 구조를 구비한 래버린스 보의 홍수안정성 및 유사연속성에 대한 효과를 3차원 수치모형(FLOW-3D)을 통해 분석하였다. 수치모의에 사용된 수로 연장은 9.25 m이고 폭은 0.82 m이며, 상류의 수심변화에 따라 수치모의를 수행하였다. 수치모의 결과 에너지 감세 효과와 상류의 수심을 유지하는 효과가 나타났다. 또한 이격된 벽체로 흐르는 유속에 의해 래버린스 보 내의 마찰속도가 증가하였다. 이러한 결과, 퇴적방지 구조를 구비한 래버린스 보가 홍수 안정성 및 유사배제에 효과가 있는 기술로써 가능성이 있는 것으로 판단된다. 향후, 수리모형실험을 통한 연구가 수행된다면 수리특성에 관한 기초자료를 통해 설계 인자가 도출될 수 있을 것이며 나아가 기술의 상용화에도 크게 기여할 수 있을 것이다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.2
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• pp.71-76
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• 1981

In order to make a numerical modeling for the one dimensional unsteady flow which expressed by Saint Venant partial differential equations, Preissmann's implicit scheme was used, and it's stability and accuracy was mentioned. By introducing recurrence relations make it possible to use double sweep algorithm. Effective parameters to the result were the values of the $\Delta$t/$\Delta$x, $\theta$ and the chezy coefficient. In oder to get numerical solutions with enough accuracy, $\Delta$t/$\Delta$x should not be far from the value of 1, and the criteria of the $\theta$ was 0.6<$\theta$<1.0 for the stability without condition. This model should be calibrated by real field data, and expected to be developed for the simulation of the river system and to the long wave analysis for one dimensional coastal zone problem.