• 대한기계학회논문집B
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• 제27권8호
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• pp.1174-1181
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• 2003

The flow around a circular cylinder was controlled by attaching O-rings to reduce drag force acting on the cylinder. Four experimental models were tested in this study; one smooth cylinder of diameter D (D=60mm) and three cylinders fitted with O-rings of diameters d=0.0167 D, 0.05D and 0.067 D with pitches of PPD=2D, 1D, 0.5D and 0.25D. The drag force, mean velocity and turbulence Intensity profiles in the near wake behind the cylinders were measured for Reynolds numbers based on the cylinder diameter in the range of Re$_{D}$=7.8$\times$10$^3$~1.2$\times$10$^{5}$ . At Re$_{D}$=1.2$\times$10$^{5}$ , the cylinder fitted with O-rings of d=0.0167D in a pitch interval of 0.25D shows the maximum drag reduction of about 5.4%, compared that with the smooth cylinder. The drag reduction effect of O-rings of d=0.067D is not so high. For O-ring circulars, as the Reynolds number increases, the peak location of turbulence intensity shifts downstream and the peak magnitude is decreased. Flow field around the cylinders was visualized using a smoke-wire technique to see the flow structure qualitatively. The size of vortices and vortex formation region formed behind the O-ring cylinders are smaller, compared with the smooth cylinder.der.

• 농촌계획
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• 제22권3호
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• pp.71-80
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• 2016

Korea is becoming a model country for the developing countries' agricultural and rural development. Drawing implications for Vietnam from Korea's experiences can help make development strategies and policies for other developing countries including North Korea as well as for Vietnam itself. Vietnam is facing an inefficiency in agricultural production and the gap between urban and rural growth has been widening. Farm sizes per household are small and farmlands are scattered. Diversification in rural industry is very restricted. To attack these problems, investment is urgently needed for rural infrastructure building as well as agricultural structure adjustment. In the process of rural development, there have been also encountered such problems as financial procurement, community's spontaneous participation, manpower development for adjusting to industrial structural change. Korea's experiences may be helpful for establishing rural development strategies and policies in Vietnam. Benchmark scopes can go beyond Saemaul Undong in 1970s. Korea's pre- and post-Saemaul Undong era as well as the Saemaul Undong era can be referred. In the wake of globalization, Vietnam has not only experienced compressed rapid economic growth but also encountered policy tasks to eradicate poverty, to realize self-reliance and income increase, and to lessen urban-rural development gap, at the same time. Korea's experiences show that priority needs to be put on the establishment of national and rural development strategies based on Vietnam-specific conditions, utilization of village's resources including community tradition and social capital, fund raising for rural development, farmland development and mobilization, production and living infrastructure building, technology transfer for farmers and vocational training for new job seekers.

• 한국안전학회지
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• 제27권1호
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• pp.20-25
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• 2012

The purpose of the study is to assess the extinguishing concentration of inert gases in engine nacelle fire. The experiment was performed with a two dimensional rectangular bluff body stabilized flames, where the fuel was ejected to counter flow and co-flow against an oxidizer stream. Two inert gases, $CO_2$ and $N_2$, were used for extinguishing agent in the oxidizer and methane was used for fuel. The main experimental parameters were the direction of injecting fuel, the kinds of agent and the velocity ratio between air and fuel streams, which controlled the mixing characteristic near bluff body and the strength of recirculation zone in the downstream. The result shows the flame structure and the mode were strongly dependent with fuel/air ratio and the fuel jet direction. For both flow configurations, the extinguishing concentration of $CO_2$ was smaller than the $N_2$ because of the large heat capacity of $CO_2$. However, the concentration of inert gasesat blowout was much smaller than those in the cup burner and coflow jet diffusion flames, which implies that the extinction mechanism of bluff body stabilized flames was mainly due to the aerodynamic aspect. Compared to co-flow fuel injection, the extinguishing concentration of inert gases under counter flow configuration was lower. The effect of direction might result from the mixing characteristic and strength of recirculation zonearound a bluff body. More details should be investigated for the characteristic of recirculation zone in the wake of bluff body using the LES(Large Eddy Simulation).

• 한국산학기술학회논문지
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• 제13권3호
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• pp.1346-1351
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• 2012

해상풍력발전기초의 국부세굴을 평가하기 위하여 3차원 수치해석인 FLOW-3D를 이용하여 모노파일과 자켓기초에 대해 해석을 수행하였다. 수치해석 결과에 의하면 모노파일과 자켓기초 레그 주위에서 국부적으로 유속이 증가하는 것으로 나타났으며, 그 후면에서는 후류 및 와류로 인하여 유속의 감소가 나타났다. 자켓기초의 경우에는 모노파일에 비해 단일 레그의 직경이 작고, 자켓레그 사이의 간섭효과 및 자켓구조물의 복잡한 형상으로 인하여 모노파일에 비하여 국부적인 유속 증가가 더 크게 나타났으며 세굴심이 더 깊게 형성되는 것으로 나타났다. 따라서, 해상풍력발전 기초의 세굴 평가 및 세굴방지공 설계시 하부구조물의 형상에 대한 고려가 필요한 것으로 판단된다.

• 건축역사연구
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• 제10권4호
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• pp.7-21
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• 2001

This study is to analyze site layout traditional government office building focused on Chonui-hyon(全義縣) in Chungchong province with Chungchong-do regional maps(忠淸道地方地圖) and Eupjis(邑誌, topography) being compiled in the late Chosun dynasty. The conclusion of analysis can be summarized as follows; 1. Chonui-hyon(全義縣) in Chosun dynasty is gone with a planning principle of the capital city(Han-Seong, 漢城) with disposing Sa-Ji-Dan(社稷壇) and Gaek-Sa(客舍), which are placed to the left and right of Eupchi(邑治), and it is followed in the wake of the spatial structure of Chosun dynasty palace with disposing Dong-Heon(東軒) in front, Nae-A(內衙) at the back of it, or from side to side, also by the Dong-Heon of the center, with organizing each facility around it. 2. Dong-Heon and Gaek-Sa of Chonui-hyon is passed through three step gate, Mun-Ru(門樓), Woi-Sammun(外三門), Nae-Sammun(內三門), from Hong-Salmon(紅門), and are shown hierarchy by haying been placed at the end of approach axis. 3. Dong-Heon can be disposed by Feng-Shui(風水) which have influence on the southeast direction with Jin-San(鎭山) and An-Dae(案對), on the other hand, Gaek-Sa can be disposed by symbolic of the authority of a king. 4. Site layout by function of provincial government office is provided into four ferrite, Dong-Heon, Gaek-Sa, Nae-A, practical business territory, and eve territory is organized by official institution on a social position to radiation, by the compositive axis to be made Woi-Sammun Nae-Sammun Dong-Heon Nae-A 5. Approach process of Chnui-hyon government office is three door system similar to Kam-Young(監營) in a different way two door system in most provincial government office, also approach axis is formed by bending.

• Asian Journal for Public Opinion Research
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• 제8권2호
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• pp.105-125
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• 2020

The purpose of this paper is to analyze 1) who created and distributed fake news, 2) the distribution channels of fake news, 3) who fake news has targeted, and 4) the effects on voting and the impact of fake news on Korean politics. In South Korea, fake news was mainly created by candidates or election campaigns. The reason is that in the wake of the impeachment of President Park Guen Hye, all the political parties in Korea used fake news as a means of mobilizing supporters for each of their candidates or parties to gain an advantage in situations involving political divisions and confrontations between the pro-impeachment, progressive young generation and anti-impeachment, conservative senior generation. Voters' media usage patterns were polarized through social network services (SNS) media and television. Fake news was mostly received through these two media outlets. According to the spreading structure of fake news in Korea, the younger generation generally uses SNS posts intended for unspecified individuals, and the older generation uses closed SNS like KakaoTalk or Naver's BAND. In the end, it is typically characteristic of the older generation to spread fake news through existing offline human networks. In the 2017 presidential election, fake news has been confirmed to have the effect of mobilizing supporters for each political party. In the presidential election, an increase in voter turnout was confirmed among those in their 20s and those in their 60s or older. Evidently, fake news influenced the election of Moon Jae-In. The influence of fake news is expected to grow further as ideological polarization and consequent political polarization continues to intensify in South Korea.

• 한국항공우주학회지
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• 제35권1호
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• pp.1-9
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• 2007

검정금파리 날개의 “8자 운동”에 의한 공기역학적 힘의 발생에 관해 수치해석을 수행하였다. 날개운동은 자유류가 있는 tethered flight 실험에서 관찰된 결과에서 인용하였다. 해석결과 양력은 downstroke 중일 때 주로 발생하였고 추력은 upstroke 끝에서 갑작스럽게 발생하였다. 본 연구에서는 양력과 추력 발생의 이러한 특성을 후류에서의 와류구조와 에어포일 주위의 압력장을 통해 물리적으로 이해하고자 하였다. 결과적으로 양력발생은 유효받음각의 증가에 따른 앞전와류와 관계있었으며, 추력발생은 유동장 형태의 측면에서 와류 짝(vortex pairing)현상과 압력장 측면에서 와류정지 현상으로 설명할 수 있었다.

• 대한기계학회논문집B
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• 제34권10호
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• pp.901-906
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• 2010

복잡한 지형에 위치한 풍력발전소의 유동장을 분석하기 위해 3차원 유동해석이 수행되었다. 본 논문의 목적은 복잡한 지형과 풍력발전기의 배치가 풍력발전소의 성능에 미치는 영향을 연구하는 것이다. 자세한 블레이드 형상을 고려한 총 49대의 풍력발전기가 계산 도메인에 포함되었다. 풍력발전기의 회전운동을 고려하기 위해 고정회전자 기법이 사용되었고, 블레이드에 작용하는 토크를 계산함으로써 풍력발전기의 성능을 평가하였다. 수치해석 결과를 통하여 풍력발전소 전체의 자세한 유동장과 지형적 영향으로 풍속이 감소되는 국부적인 영역을 예측하였고, 상류의 발전기에서 발생하는 후류가 하류에 위치한 발전기의 성능에 미치는 영향도 분석되었다. 본 연구의 해석기법은 추후 건설되는 풍력발전소의 부지와 풍력발전기의 최적 위치를 선정하는 데 사용될 수 있을 것으로 사료된다.

• 대한기계학회논문집
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• 제13권4호
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• pp.780-788
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• 1989

본 연구에서는 재부착 이후의 재발달 난류경계층에서의 난류구조와 비평형 상태에서 평형상태로의 변화 과정을 실험적으로 고찰하고자 한다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2005년도 추계학술대회 논문집
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• pp.135-140
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• 2005

항만과 해역에 설치되는 수직벽의 일례로 육상 및 유입되는 오염수의 오염 유출 방지를 위한 차수기능을 갖는 차수벽과 교량이나 댐, 갑문 둥의 하천 또는 해양구조물을 축조하는 동안 물이 들어오는 것을 방지하기 위하여 임시로 설치되는 가물막이(cofferdam)벽 등이 있다 이들 차단벽의 구조역학적인 설계 인자 중 유입수 유동 특성과 설치 지역의 지반 특성이 중요한 의미를 가진다고 판단된다. 본 연구에서는 이러한 수직 차단벽 주위의 유체역학적 특성 파악의 일례로 수직벽의 하단에 틈새를 갖는 파공(perforation)이 발생하였을 때 이들 파공의 개도율 변화에 따른 유동특성을 고찰하는 하나의 방안으로 입자영상유속계(Particle Image Velocimetry)를 이용하여 수직벽 후류 특성을 실험적으로 고찰하였다.