• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.115-120
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• 2018

This study examined the cast quality of small-sized induction motor rotors during the die casting process. Numerical analyses with 3-dimensional half models were performed to investigate the filling patterns of aluminum molten metals into a mold after high-speed injections. The following were obtained from numerical analyses and experimental results. First, molten metals started to fill the lower end ring, then moved horizontally to fill the core slot and upper end ring, and finally stopped to fill the rotor core slot. Second, circulation of molten metals occurred at the lower end ring, resulting considerable porosity at the section of lower end ring from the experimental results. Third, further work for obtaining sound quality of rotor core cast is required to develop a new shape of the rotor core cast or improve the die casting conditions.

• Journal of the Korean Solar Energy Society
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• v.26 no.3
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• pp.17-24
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• 2006

최근에 에너지절약 차원에서 종래의 공조방식을 대신할 새로운 냉난방시스템 개발이 요구되고 있는데, 본 논문에서는 태양열 집열기를 이용하는 데시컨트 시스템 중 제습역할을 실질적으로 담당하는 제습기의 충진층 부분에서의 열 및 물질전달에 관한 일련의 해석 결과를 발표하고 있다. 제습과정에서 액체흡수제는 충진층에서 열 뿐만 아니라 물질전달을 수반하게 되는데, 이 결과 건물에 냉방 및 난방효과를 가져다 준다. 따라서 이 충진층의 최적 설계가시스템의 효율을 극대화하기 위해서는 무엇보다도 중요한데, 이를 위해서는 충진층에서의 열 및 물질전달 양상을 규명하여야 한다. 따라서 금번 실험에서는 공기와 액체흡수제와의 접촉면적을 넓히기 위해서 충진재로써 3cm(직경) ${\times}$ 3cm(높이)인 시판중인 플라스틱 재질을 사용하고, 실질적으로 40cm(너비)${\sim}$40cm(깊이)${\times}$40cm(높이)의 충진층을 직접 제작하여 실험을 행하였다. 그 결과, 공기측 열 및 물질전달 계수는 공기 온도와 밀접한 관계를 갖고 있으며, 또한 물질전달계수는 열전달계수와 같은 경향을 보이고 있음을 알 수 있었다.

• Journal of the Korean association of regional geographers
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• v.22 no.3
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• pp.628-642
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• 2016

In small countries such as Korea, rapid expansion of cities has been pointed out as the main cause of urban and environmental issues. In order to understand the urban problems caused by urban sprawl and prepare countermeasures for it, urban sprawl must be accurately measured first of all. The purpose of this study is to analyze the spatio-temporal changes of urban sprawl process in Seoul Metropolitan Area using landscape indices which measure the degree of urban sprawl in terms of urban structure such as area, distribution, and shape of urbanized area. FRAGSTATS, which is a tool for landscape analysis, is utilized to calculate landscape indices. Major findings are as follows. First, the urban sprawl in Seoul Metropolitan Area has been continually intensified since the late 1980s and this tendency was more clearer in the 1990s than the 2000s. While leapfrog development is relatively prominent in the 1990s, infilling development is remarkable in the 2000s. Second, the progress and development types of sprawl progress were different according to the zones which are defined based on Seoul Metropolitan Area Readjustment Planning Act. Congestion Restrain Zone shows the highest level of urban sprawl in terms of the evaluated landscape indices, but infilling development was predominant. In Growth Management Zone1, leapfrog development was dominant in the 1990s and infilling development in the 2000s. In Growth Management Zone1, leapfrog development has been continually remarkable since the late 1980s. Nature Conservation Zone shows the lowest level of sprawl, but its sprawl tendency is gradually being intensified. Third, the sprawl tendency in Seoul Metropolitan Area was different according to the distance and direction from Seoul. Urban sprawl was remarkable at Si-Guns close to Seoul in the late 1980s, Si-Guns close to Seoul and the southern part of Seoul in the late 1990s, and the southern and northern parts of Seoul in the late 2000s.

• Journal of Korea Foundry Society
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• v.17 no.6
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• pp.552-559
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• 1997

주조방안설계를 위한 pre-processor, main-solver 그리고 post-processor로 구성된 통합 응고해석 시스템을 개발하였다. Pre-processor는 퍼스널 컴퓨터에서 사용되는 상용 CAD 프로그램인 AutoCAD를 사용하였다. Main-solver는 주조과정중의 충진거동을 해석한 유동해석 프로그램과 3차원 열전달 응고해석을 통합하여 냉각수 시스템으로 제어되는 금형 반복주조법에서의 응고양상을 해석할 수 있다. Post-processor는 cavity내의 용탕충진거동, 주형내의 온도분포, 응고시간등을 3차원 그래픽으로 처리할 수 있게 설계하였다. 개발된 시스템의 현장적용 가능성을 검증하기 위하여 대형주강 밀하우징, 자동차휠 주조용품, 밸브블럭등의 시제품의 열유동해석에 적용하였다. 본 연구에서 개발된 CastDesigner는 중소기업형 주조현장에서 PC용 CAD/CAE system 구축을 통한 최적주조방안 설계용 열유동해석 프로그램으로 사료된다.

• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.3
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• pp.116-121
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• 2004

Treatability tests were conducted to study the feasibility of EMMC process as a recycling-water treatment system in high density seawater aquaculture farm. To study the effect of organic and ammonia nitrogen loading rate on system performance, hydraulic retention time was reduced gradually from 12hr to 10min. The conclusions are can be summarized as follows. When the system HRT was reduced from 12hr to 2hr gradually, there was little noticeable change(reduction) in ammonia nitrogen removal efficiencies. However, removal efficiencies were decreased dramatically when the system was operated under the HRT of less than 2hr. In case of organics(COD), there was no dramatic change in removal efficiencies depending on HRT reduction. COD removal efficiencies were maintained successfully higher than 9％ when the system was operated at tile HRT of 10 min. System performances depending on media packing ratio in the reactors were also evaluated. There were little differences in each reactor performances depending on media packing ratio in reactor when the reactors were operated under the HRT of longer than 1hr. However, differences in reactor performances were considerably evident when the reactors were operated under the HRT of shorter than 1hr. When comparing reactor performance among 25％, 50％,7 5％ packed reactor, it can be judged that media packing ratio more than 50％ plays no significant role in increasing reactor performance. For this reason, packing the media less than 50％ is more reasonable way in view of economic. Such a tendency shown in COD removal efficiencies well agreed with the variation of ammonia-nitrogen removal efficiencies according to the media packing ratio in reactors at each HRT. Difference in effluent ammonia-nitrogen concentration between 50％ media packing reactor and 75％ media packing reactor was negligible. When comparing with the results of 25％ packing reactor, difference was not so great.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.347-352
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• 2019

This study focused on improving the cast quality of small-sized induction motor rotors during the die casting process. A new rotor core cast model was proposed based on previous research results and parametric studies. Numerical analyses using 3-dimensional half models were performed to evaluate the filling patterns of aluminum molten metals into a mold and on-site experiment performed to verify the newly proposed cast model. The following were obtained from numerical filling analyses and experimental results. First, molten metals started to fill the lower end ring, then moved on to fill the core slot and upper end ring and finally stopped to fill at the rotor core slot. Second, significant circulation of molten metals was not observed on the lower end ring, resulting in fewer defects at the section of the lower end ring from the experimental results. Third, the new shape of a rotor core cast was effective in producing rotors with sound cast quality, and reducing the end ring cast defect area by approximately 70 %.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.336-339
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• 2005

포천지역의 포천천과 그 주변의 8개 소유역을 대상으로 2003년 8월부터 2004년 8월까지 하천 8개 지점과 기존 지하수 관정 66개소를 선정하여 수리지구화학 및 환경동위원소 연구를 실시하였다. 복합적인 토지이용과 관련하여 연구지역 수계에서는 오염물질 유입이 광역적으로 인지되었으며, 일부 지역에서는 지하수계로의 오염물질 유입이 강하게 나타나 인근 하천까지 영향을 줌이 확인되었다. 오염기원으로 해석되는 대표적인 무기이온종인 $NO_3,\;Cl,\;SO_4$의 존재비를 이용하여 연구 지역의 지표수와 충적 지하수를 크게 3개 수질 그룹으로 분류하였다. 이들 그룹들은 각각 특징적인 충진 특성과 용존 이온의 분포/거동 양상을 나타내는 것으로 해석된다. 본 논문에서는 세 유형의 지표수/충적 지하수 외에 암반 지하수를 포함하여 연구지역 자연수의 수리지구화학 진화 경로와 오염물질의 유입 및 거동 양상에 대하여 토의한다.

• Journal of Conservation Science
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• v.25 no.2
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• pp.131-145
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• 2009

Goryeong Yangjeondong Petroglyph on the joint face of the bedrock (6m in width, 3m in height) composed of the green sandstone has circles and shield pattern sculptures. The rock is mainly composed of quartz, feldspar, chlorite, illite and calcite with the clay minerals. These clay minerals occur as pore lining, replacement of component and pore fillings. Investigated the weathering aspects including the connection between soluble salt and rock weathering and the stability of the bedrock with petroglyphs. The Major deterioration aspect are grain peel-off, surface exfoliation, cracks and damage. And the bedrock where the joints and cracks advance is interpreted with the fact that has the possibility of the falling rock. For conservation, adhesive need to cover crack and damage and consolidation is necessary in the surface which becomes weak.

• Korean Journal of Food Science and Technology
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• v.40 no.4
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• pp.460-465
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• 2008

This study examined the effect of head formation on the quality maintenance of minimally processed lettuce (Lactuca sativa L.) samples. The fresh-cut lettuce samples were packed in $20{\times}15{\times}5$ cm polypropylene+polyethylene terephthalate tray, and were then stored at $4^{circ}C$ for up to 8 days. According to the results, the sample with 100% head formation had lower sugar, minerals (Ca, Na, Fe, Mg, K), and chlorophyll contents compared to the sample with 70% head formation. The 70% head formed lettuce had higher vitamin C content at 3.30 mg/100 g, whereas the 85% and 100% formed samples had lower levels of 2.61 and 2.10 mg/100 g, respectively. The polyphenol oxidase (PPO) activity of the 70% formed lettuce was 240 unit/g, while the 100% formed sample had almost 2-fold higher activity. However, the 100% formed lettuce had greater firmness than all other samples. Overall, among the fresh-cut lettuces, the sample with 70% head formation showed more positive effects in terms of quality maintenance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.135-144
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• 2009

The present paper represents experimental studies on the performance of concrete filled FRP columns. Eight scale-down specimens were conducted by quasi-static cyclic loading test. FRP thickness, concrete strength, horizontal rebar ratio, and diameter were selected as test parameters. The capacities of ductility for cyclic loading was evaluated and the damping ratio and failure mode from the stiffness reduction of each test specimen were compared.