• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계합동학술대회 논문집
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• pp.172-175
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• 2002

The technique of induced discharge by a pulsed CO2 laser is being applied to control electrical discharge path, material processing, triggered lightning for protecting the power equipments. In this paper, we have investigated about the characteristics of the induced discharge at atmospheric conditions by using a plasma channel, which is produced when a pulsed CO2 laser radiation is focused by a focusing mirror as a trigger source. A plasma channel produced by laser radiation has an effect on decreasing the threshold voltage and inducing the discharge in both needle electrodes. We have confirmed a delay time between a produced plasma channel and an electrical discharge after laser radiation. We provided the decreased voltage lower than the natural discharge voltage between electrode type of needles and was induced the discharge by forming a plasma channel between them. In this research we could understand the time delay of induced discharge by laser radiation, and the characteristics of the discharge cause by the decrease in the threshold voltage, and the polarity effect by changes of plasma channel positions between two electrodes.

• Tribology and Lubricants
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• 제33권1호
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• pp.1-8
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• 2017

Drag torque reduction in a wet clutch pack is a key aspect of the design process of the dual clutch transmission (DCT) system. In order to reduce the drag torque caused by lubricant shear resistance, recently developed wet clutch pack systems of DCT, as well as automatic transmission and other four-wheel drive (4WD) couplings, frequently utilize wavy wet clutch pads. Therefore, wavy shape of friction pad are made on the groove patterns like waffle pattern for the reduction of drag torque. Additionally, the groove patterns are designed with larger channels at several locations on the friction pad to facilitate faster outflow of lubricant. However, channel performance is a function of the waviness of the friction pad at the location of the particular channel. This is because the discharge sectional area varies according to the waviness amplitude at the location of the particular channel. The higher location of the additional channel on the friction pad results in a larger cross-sectional area, which allows for a larger flow discharge rate. This results in reduction of the drag torque caused by the shear resistance of DCTF, because of marginal volume fraction of fluid (VOF) in the space between the friction pad and separator. This study computes the VOF in the space between the friction pad and separator, the hydrodynamic pressure developed, and the shear resistance of friction torque, by using CFD software (FLUENT). In addition, the study investigates the dependence of these parameters on the location and waviness amplitude of the channel pattern on the friction pad. The paper presents design guidelines on the proper location of high waviness amplitude on wavy friction pads.

• 조명전기설비학회논문지
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• 제20권1호
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• pp.85-90
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• 2006

본 논문은 불평등 전계의 $SF_6/CO_2$혼합기체 중에서 전구방전특성에 대한 실험결과를 제시한다. 임펄스 전구방전 진전을 코로나 전류와 방전광 이미지의 측정으로 조사하였다. 정 부극성의 전구방전 진전메커니즘은 기본적으로 같았으며, 초기스트리머코로나는 침전극의 끝단에서 발단되어 계단상으로 진전하는 리더에 의해 시험갭을 교락시킨다. 정극성에서 리더펄스의 휴지시간은 부극성에서보다 매우 짧았다. 또한 부극성에서 초기스트리머코로나와 절연파괴사이의 시간간격은 정극성에서보다 매우 길게 나타났다. 정극성에서 방전채널경로는 임의적으로 나타났으며, 부극성에서 리더 채널은 정극성에서 보다 굵고 밝게 나타났다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.3-4
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• 2009

As device process technology advances, effective channel length, the thickness of gate oxide, and supply voltage decreases. This paper describes a novel electrostatic discharge (ESD) protection device which has current feedback for high ESD immunity. A conventional Gate-Grounded NMOS (GGNMOS) transistor has only one ESD current path, which makes, the core circuit be in the safe region, so an GGNMOS transistor has low current immunity compared with our device which has current feedback path. To simulate our device, we use conventional $0.18\;{\mu}m$ technology parameters with a gate oxide thickness of $43\;{\AA}$ and power supply voltage of 1.8 V. Our simulation results indicate that the area of our ESD protection, device can be smaller than a GGNMOS transistor, and ESD immunity is better than a GGNMOS transistor.

• Journal of Biosystems Engineering
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• 제42권1호
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• pp.1-11
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• 2017

Purpose: Methods: Three-dimensional CFD modeling was conducted to analyze the flow structure and discharge flow rate corresponding to the variation in the geometry of the flow channel in a microtube. Additionally, experiments were carried out, and the discharge flow rate was measured at various inlet pressures and inclination angles of the microtube. Results: The quantitative data of velocity distribution and discharge flow rate were obtained. As the width and length of the microtip increased, the discharge flow rate decreased significantly because of the increase in the loss of pressure along the microtube. As the depth of the microtip increased, the flow rate also increased because of the reduction in the flow resistance. However, in this analysis, the variation in the angle of the microtip did not influence the flow rate. From the experimental results, it was observed that the flow rate increased linearly with the increase in the inlet pressure, and the effects of the inclination angle were not clearly observed in those test cases. The values of the flow rate obtained from the experiments were significantly lower than that obtained from the CFD analysis. This is because of the distortion of the shape of the flow path inside the microtube during the fabrication process. The distortion of the flow path might decrease the flow cross-sectional area, and it would increase the flow resistance inside the microtube. The variation in the flow rate corresponding to the variation in the inlet pressure showed similar trends. Conclusions: Therefore, the results of the numerical analysis obtained from this study can be efficiently utilized for optimizing the shape of the microtip inside a microtube.

• 공업화학
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• 제32권6호
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• pp.613-620
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• 2021

고분자전해질 연료전지의 유로 형상은 내부 유동의 균일성에 영향을 주는 변수이다. 유로 내에서 반응물 분포가 균일하지 않을 경우, 지속적인 운전 과정에서 촉매의 열화 및 고분자 막의 기계적 손상이 야기되며 연료전지의 내구 수명 저하로 이어진다. 연료전지에서 원활한 반응물 공급과 균일한 농도 분포를 위하여 유로 형상에 관한 연구들이 활발히 진행되고 있다. 유로의 배플은 유체의 강제 대류를 야기해 연료전지의 성능을 개선할 수 있고, 유로 중간에 새로운 반응물 공급 통로(서브 채널)를 만들어 반응물 농도 증가와 원활한 물 배출로 물질 전달 손실을 감소시킬 수 있다. 본 연구에서는 전산 유체 계산을 통하여 블록과 서브 채널을 적용한 유로가 연료전지의 전류밀도와 산소 농도에 미치는 영향을 분석하였다. 블록과 서브 채널이 유로에 구성되었을 때, 한계전류밀도가 증가하였고 블록 후단의 산소 농도가 회복되었다. 블록이 2개 이상 있을 때 블록 사이에 서브 채널을 배치할 경우 전류밀도 증가 폭이 더욱 커졌다. 또한 추가 공급되는 공기의 공급 위치에 따른 산소 농도를 분석하여 서브 채널이 블록 후단의 낮아진 산소 농도를 회복할 수 있었다.

• 자원환경지질
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• 제27권6호
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• pp.579-592
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• 1994

A case study is presented where a fluvial system is modeled in three dimensions and compared to data gathered from a study of the Arkansas River. The data is unique in that it documents changes that affected a straight channel that was excavated within the river by the U.S. Army Corps of Engineers. Excavation plan maps and sequential aerial photographs show that the channel underwent massive deposition and channel migration as it returned to a more natural, meandering path. These records illustrate that stability of fluvial system can be disrupted either by catastrophic events such as floods or by subtle events such as the altering of a stream's equilibrium base level or sediment load. SEDSIM, Stanford's Sedimentary Basin Simulation Model, is modified and used to model the Arkansas River and the geologic processes that changed in response to changing hydraulic and geologic parameters resulting from the excavation of the channel. Geologic parameters such as fluid and sediment discharge, velocity, transport capacity, and sediment load are input into the model. These parameters regulate the frequency distribution and sizes of sediment grains that are eroded, transported and deposited. The experiments compare favorably with field data, recreating similar patterns of fluid flow and sedimentation. Therefore, simulations provide insight for understanding and spatial distribution of sediment bodies in fluvial deposits and the internal sedimentary structure of fluvial reservoirs. These techniques of graphic simulation can be contributed to support the development of the new design criteria compatible with natural stream processes, espacially drainage problem to minimize environmental disruption.

• 대한공간정보학회지
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• 제20권1호
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• pp.13-20
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• 2012

본 연구의 목적은 유역 하천망의 발달에 따른 수문응답함수의 변화양상 분석에 있다. 이를 위한 대상유역은 보청천의 탄부수위표를 출구로 하는 소유역을 선정하였다. 적용된 하천망은 Strhler 차수분류법에 의해 구성된 하천망과 유역 내 모든 격자가 하천 또는 지표면으로 구성된 경우로 총 10가지로 구성하였다. 각각의 경우에 대해 대상유역 내 모든 격자의 지표면과 하천 배수경로 길이를 산정하였으며 Nash 모형을 이용하여 수문응답함수를 결정하였다. 분석결과 하천망이 발달함에 따라 수문응답함수의 첨두유량은 크게 나타나며, 첨두시간은 작아지는 양상을 보였다. 또한 응답함수의 통계적 특성을 살펴 본 결과 하천망의 발달에 따라 유하시간의 평균(지체시간)과 분산이 지수적으로 감소함을 알 수 있었다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 춘계학술대회논문집
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• pp.57-60
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• 2005

This paper describes the experimental results of the pre-breakdown phenomena in $SF_6/CO_2$ mixtures under non-uniform electric fields caused by positive and negative lightning negative voltages. $SF_6/CO_2$ mixtures have an advantage of an environmental aspect and cost reduction, and safety aspects. In order to analyze the pre-breakdown processes in $SF_6/CO_2$ mixtures stressed by impulse voltages, pre-breakdown current and luminous signals were measured by a shunt and a photo-multiplier tube, respectively. Dielectric strengthes of $SF_6/CO_2$ mixtures were investigated. Additionally, characteristics of discharge channels were observed by high speed cameras and the physical properties were discussed. The pre-breakdown propagates with a stepwise process. The in to breakdown from the corona onset point in positive polarity was shorter than that in negative polarity. The time intervals of positive leaders are shorter than those of negative leaders, and the path of positive leader channel is zigzag.

• 환경영향평가
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• 제24권4호
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• pp.367-374
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• 2015

해수 표층 수온은 원자력발전소의 온배수 영향을 조사하기 위해서 위성원격탐사에 의해 관측되는 가장 중요한 정보들 중 하나이다. 하지만 Landsat 7 위성과 Landsat 8 위성의 열적외선 센서로부터 추출한 표층수온과 실측치를 비교한 연구는 부족하다. Landsat 8 위성은 표층수온을 추출하기 위해 열적외선 센서에 두 개의 분리된 밴드를 가지고 있지만, Landsat 7은 한 개의 밴드를 사용하고 있다. 그럼에도 불구하고 본 연구에서는 Landsat 7 ETM+센서가 Landsat 8 TIRS 보다 표층수온의 보정에 유용하다는 것을 제시하였다. 본 연구에서는 Landsat 114-36 지역의 15개 위성자료를 가지고 ENVI와 IDL을 이용한 표층수온 알고리즘을 처리하였다. 국립해양조사원으로부터 수집한 표층수온 실측자료와 위성에서 추출한 표층수온을 비교하였고, 위성관측 시계열 자료와 측정지점의 실측자료를 통해 정확도를 비교하였다.