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차성운(Cha Sung Woon),김대은(Kim Dae-eun),이수홍(Lee Soo-hong),이경수(Lee Kyung Soo),김민수(Kim Minsoo) 한국공학교육학회 2007 공학교육연구 Vol.10 No.4
현재 대학의 공학교육은 산업계 수요를 반영한 인재 양성에 적합한 교육을 하고 있지 못한 것이 현실이 며, 이에 대한 극복을 위하여 대학과 정부에서는 새로운 교육모델의 개발을 위하여 많은 노력을 하고 있다. 본 연구는 공학에서 가장 중요한 분야 중 하나인 설계분야에 적합한 현장 적응형 인재를 양성하기 위한 공학설계 교육의 방향을 살펴보는데 있다. 설계기술역량과 ABEEK의 학습성과 문항을 설문 문항으로 이용하여 산업체, 교수 그리고 학생의 입장에서 창의설계프로젝트 (3)라는 공학설계 교육을 어떻게 바라보는지 비교, 분석하여 공학설계 교육의 방향을 제시하였다. 이를 위해 휴대전화 업체의 기구설계 분야의 전문가들을 통해 설계자가 설계업무 수행을 위해서 반드시 갖추어야할 필수 역량인 설계기술역량 3요소를 선정하였 다. 또, 이 3요소에 기반한 교수의 교육목표, 학생의 학습성과 그리고 산업체에서 생각하는 교육방향을 도출하고, 이를 비교 분석한 결과 창의설계프로젝트 (3)의 공학설계 교육이 산업체의 설계분야 요구사항을 유사하게 반영하고 있음을 확인하였다. that current engineering education is insufficient to cultivate engineers who can fulfill industrial demands. Engineering colleges and the government have expended much effort to develop new education model to overcome these shortcomings. The purpose of the present research is to formulate direction of engineering design education to cultivate talented engineers meeting engineering and industrial needs. We compared and analyzed Creative Design Project (3) (a core subject in engineering design) from the feedback of practising engineers, professors and students based on essential design technology factors and the educational achievement contents of ABEEK. The three essential factors of design technology which are prerequisites for the designers to implement design work were selected by surveying experts in the field of device design of cellular phone company. Moreover, educational purpose of the professors, educational achievement of the students, and educational direction of industry needs are deduced based on the three factors. It is also ascertained that Creative Design Project (3) meets most of the requirements of industrial design field by comparing and analyzing deduced results.
차금환,김대은,Cha, Kum-Hwan,Kim, Dae-Eun 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.12
It has been well established that resistant force and wear that occur during rolling motion depend on several factors such as material type, hardness, subsurface microstructure, applied load, and speed. The purpose of this work is to investigate the effect of microstructure and the state of deformed layer on the rolling contact characteristics in dry and lubricated rolling contacts. The results of this work show that the rolling resistance behavior depends on the state of the deformed layer. Also, lubrication can reduce the plastic flow at the surface but may still have an effect on the subsurface strain. The cross-sectional view of the microstructure shows that surface traction has a difinite effect on the morphology of the surface region. That is, significant slip seems to have taken place between the ball than those of the dry rolling case. The surface generation effects were significantly less compared to the case of dry rolling contact.
다중 직렬 연결된 대용량 EDLC 모듈에 적합한 전압 밸런싱 기법에 대한 연구
차대중(Dae-Joong Cha),백지은(Ji-Eun Baek),고광철(Kwang-Cheol Ko) 한국조명·전기설비학회 2015 조명·전기설비학회논문지 Vol.29 No.7
In this paper, the problem of voltage unbalancing in series-connected multiple electric double-layer capacitors(EDLCs) is studied. Good understanding of this problem is required in order to increase reliability and stability of an energy storage system comprising EDLCs. Existing methods to settle voltage unbalancing cannot mitigate the problem enough for each cell, since most method have been applied to each module. For equalizing between cells, Zener diode which is one of passive method have been well examined in literature. However, Zener have well not used in balancing due to heating problem. In addition, It is difficult to choose Zener diode fitted rating voltage of EDLC, because of its internal resistance. Thus, we proposed passive balancing using Zener diode by analyzing parasitic element of Zener and EDLC. To experimentally confirm the balancing effect, we compared in two occasions which are with and without passive. As a result, proposed passive balancing circuit mitigated unbalanced voltage gap between EDLCs.
변압기 없는 고승압 직류 컨버터용 대칭형 Cockcroft-Walton 회로
차대중(Dae-Joong Cha),백지은(Ji-Eun Baek),고광철(Kwang-Cheol Ko) 한국조명·전기설비학회 2015 조명·전기설비학회논문지 Vol.29 No.8
High Step-up DC-DC Converters have been demanded for renewable energy applications. Transformer or coupled inductor is generally used to boost output voltage of converters. This methods can relatively obtain high voltage than others, whereas have heavy weight and high cost. To complement these disadvantages, we studied transformerless high step-up DC-DC converter. In various transformerless topologies, Boost converters combined with Cockcroft-Walton have studied. In this paper, we proposed a symmetrical Cockcroft-Walton circuit for transformerless high step-up DC-DC converter. Finally, we simulated proposed converter to compare with existing converter. As a result, proposed converter has higher duty ratio or lower cost than existing transformerless converters which are discussed in this paper.
전류전도모드에 따른 Interleaved ZCT DC-DC Converter의 스위칭 손실 분석
차대중(Dae-Joong Cha),백지은(Ji-Eun Baek),고광철(Kwang-Cheol Ko) 한국조명·전기설비학회 2015 조명·전기설비학회논문지 Vol.29 No.1
In the issues of interleaved topology which have been in limelight as high power converter, various soft-switching methods are studied to reduce switching losses in high power application. The interleaved ZCT converter has an additional filter inductor to reduce losses of diodes during reverse recovery process. However, additional current conduction modes are occurred by the inductor, we need to analyze switching losses with inductor values on each mode. In this paper, current conduction modes and boundary conditions of interleaved ZCT converter are analyzed. In the conclusion, the minimum of switching losses in converter operation modes is analyzed by calculating switching losses.
제주연안 육상양식장 밀집지역 주변해역의 영양염 과잉 요인
고혁준,박성은,차형기,장대수,구준호,Koh, Hyuk-Joon,Park, Sung-Eun,Cha, Hyung-Kee,Chang, Dae-Soo,Koo, Jun-Ho 해양환경안전학회 2013 해양환경안전학회지 Vol.19 No.4
제주연안선 부근에 밀집된 육상양식장 배출구 주변 4개 해역(애월리, 행원리, 표선리, 일과리)에서 수질환경의 시공간적 변화에 영향을 미치는 요인을 파악하기 위해 2010년 2월부터 2011년 12월까지 격월로 총 12회 조사하였다. 주성분 분석 결과 조사해역에서 연중 영양염의 분포는 염분과의 관련성 없이 배출구로부터 공급되는 물질에 의해 영양염의 농도가 조절되어, 연안에서 외해역으로 갈수록 농도구배가 감소하는 특징을 나타냈다. 특히 용존무기질소의 경우는 배출구와 인접한 해역에서는 부영양상태로 인에 비해 질소가 과잉되고 있었다. 유기물의 분포는 담수유입량이 증가하는 고수온기에 증가하는 경향을 보였다. 식물플랑크톤의 생물량 변화는 애월 및 행원해역은 담수유입과 관련된 기상요인(기온 및 강우), 표선 및 일과는 영양염의 인위적 공급요인(양식장 배출수)에 의한 영향을 주로 받는 것으로 나타났다. 특히, 배출구로부터 직선거리 약 300 m 및 수심 10 m이내 해역의 표 저층에서는 고영양염 농도 분포가 지속되고 있어, 부영양화 과정에서 발생하는 문제를 직 간접적으로 받을 수 있는 가능성을 나타냈다. 육상양식장의 운영 시 취수지점이 배출수의 영향을 받는 지점에 위치할 경우 사육수질의 문제가 발생할 수 있다. This study investigated the temporal-spatial distribution and variations in water quality parameters (temperature, salinity, pH, DO, COD, SPM, DIN, DIP, silicate, TN, TP, and chlorophyll-a) in the coastal area of Jeju, Korea, adjacent to aquaculture ponds (Aewol-ri, Haengwon-ri, Pyosun-ri, and Ilkwa-ri). Data were collected bimonthly from February 2010 to December 2011. A principal component analysis (PCA) identified three major factors controlling variations in water quality during the sampling period. Aquaculture effluent water led to large changes in nutrient levels. The highest nutrient values were observed during the investigation period. The relatively large increase in organic matter at the sampling stations coupled with sea area runoff events during the summer rainy period. Variation in chlorophyll-a concentration was mainly driven by meteorological factors such as air temperature and rainfall in the coastal areas of Aewol and Haengwon. In the coastal areas of Pyosun and Ilkwa, pollution was caused by anthropogenic factors such as discharge of aquaculture effluent water. High nutrient concentrations at the majority of the coastal stations indicate eutrophication of coastal waters, especially within a distance of 300 m and depth of 10m from drainage channels. Coastal eutrophication driven by aquaculture effluent may be harmful inshore. Events such as eutrophication may potentially influence water pollution in aquaculture ponds when seawater intake is detected because of aquaculture effluent water.