• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.63-72
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• 2013

A Mach 5 nozzle and a diffuser of the Scramjet Engine Test Facility (SETF) were made for a hydrocarbon-fueled scramjet engine. SETF, attached with a diffuser guide, started with a model of 60% blockage, though the model engine could not start by over expansion of the facility nozzle. The model was moved into the nozzle to escape the shock generated from the nozzle exit, both SETF and the engine could start. The pitot rake experiments (blockage of 2.3%) were done for measuring the core flow in the test section. From the pitot experiments, the core flow was expanded by an under expansion. It means that the core flow in the test section was related with a model blockage. SETF and the engine with a blockage of 33% work normally. From a series of experiments, SETF started with a normal shock efficiency of 58%, regardless of a blockage ratio.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.2
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• pp.115-124
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• 2018

In this study, a cold flow test was carried out on a high-speed vehicle facility with a high-altitude environment simulator. Variable test was carried out according to the blockage ratio, angle, and length of the test model. It is confirmed that the blockage rate can be operated in the range of 40%, and that the model should be selected at an angle of 45 degrees or less. The variables of length are less dominant compared to the variables of blockage rate and angle. Through this, a database is obtained according to the parameters of the conical model of the high-speed vehicle test facility.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.5
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• pp.88-95
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• 1999

스테레오 정합에서 가장 중요하고도 어려운 문제는 대응점 추출 문제와 폐색 영역에 대한 처리이다. 특히 폐색 영역의 점들은 대응점이 존재하지 않기 때문에 변이 정보 획득에 많은 어려움이 있다. 이러한 문제에 대한 효과적인 접근을 위해 본 논문에서는 쌍방향 정합 알고리즘을 기반으로 폐색 영역의 정합 정도를 향상 시키는 방법을 제안한다. 즉 좌,우 영상 각각의 기준에 대해 독립적인 변이 정보를 구하고, 이를 바탕으로 정합의 타당성 여부를 검토하여 그 결과를 다음 처리에서 반영하는 상호 보완적인 반복 처리 기법을 적용하였다. 이 과정에서 구해진 폐색 영역에 대한 변이 정보는 스테레오 영상 모델의 기하학적 구조를 적용하여 좌, 우측 기준 정합에 대해 그 좌, 우측 점들의 변이 정보들로 대체함으로써 불연속점들의 무뎌짐(blurring)현상을 개선하였다. 한편, 실험 결과를 보다 객관적으로 비교하기 위해 정합율과 에러율이라는 파라메터를 정의하여 개선된 결과를 보였다.

• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.63-67
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• 2016

본 연구에서는 극초음속 추진기관을 위한 고공환경 모사 설비 장치에서 시험부 안에 들어가는 시험 모델의 변수에 대해 고찰하였다. 시험부에 적용할 시험 모델을 대상으로 진행하고, 시험 모델 형상 변화에 따른 유동 특성을 파악하였다. 시험 모델에 대한 주요 변수는 폐색율, 각도, 받음각으로 설정하였으며, 해석은 EDISON_CFD에서 제공하는 정렬격자 기반 2차원 압축성 유동 범용 해석 SW로 진행하였다. 해석 결과를 통해 다양한 형상 변수에 따라 변화 되는 충격파 뒤의 압력층 두께를 확인 하였고, 압력층 두께가 두꺼워 질수록 시험 조건을 모사 할 수 없음을 확인하였다. 본 연구를 통해 형상 변수에 따른 극초음속 추진기관을 위한 고공모사설비에서 시험부에 적용될 시험 모델의 범위를 확인하였다.

• Journal of Broadcast Engineering
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• v.20 no.2
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• pp.265-272
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• 2015

A new technology on video frame rate up-conversion (FRUC) is presented by combining the median filter and motion estimation (ME) with an occlusion detection (OD) method. First, ME is performed to have a motion vector. Then, the OD method is used to refine motion vector in the occlusion region. Since the wrong motion vector can be obtained with high possibility in the occluded area, a median filtering that less depends on the motion vector is applied to that area, and since the motion vector is continuous and robust in the non-occluded area, BDMC(Bi-Directional Motion Compensated interpolation) is applied to obtain interpolated image in that area. BDMC using the bi-directional motion vectors achieves good results when continuity and robustness of the motion vector is higher. Experimental results show that the proposed algorithm provides better performance than the conventional approach. The average gain of PSNR (Peak Signal to Noise Ratio) is approximately 0.16 dB in the test sequences compared with BDMC.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.4
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• pp.265-280
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• 2021

Population density due to urbanization is making people interested in underground space development and much interest in TBM construction with low vibration and noise. This led to a lot of research on TBM. However, research on the characteristics of the cutterhead opening of the TBM equipment being occluded under the ground conditions under which it is excavated is insufficient. Accordingly, a study was conducted to investigate clogging of the cutterhead opening during the shield TBM rolling. To identify the clogging of cutterhead openings in SHIELD TBM equipment, the reduced model experiment was divided into clay rate (10%, 30%, 50%, 60%), cutterhead opening rate (30%, 50%, 60%), and cutterhead rotation direction (one-way, two-way) and rotational speed (3 RPM) and conducted in 36 cases. Results of scale model test on shield TBM clogging, it was analyzed that the ground condition containing clay soil increased the clogging effect in both directions than the unidirectional rotation, and that the lower the rotational speed of the cutterhead, the less the clogging effect. Accordingly, the direction of cutterhead rotation, rotational speed and opening rate are calculated by taking into account ground conditions during ground excavation, the clogging effect can be reduced. It is believed to be effective in saving air as the clogging effect is reduced. Therefore, this study is expected to be an important material for domestic use of shield TBM.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.4
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• pp.313-321
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• 2005

Drag coefficient is one of the critical design factors to quantify the piston effect in vehicle tunnels. Several problems are raised on the drag coefficient currently applied for the ventilation system design; unverified adoption of the projected frontal area of the vehicle from the foreign study in the past, and lack of consideration for the slip-streaming effect. This study aims at better estimation of the traffic-induced ventilation force in the local tunnels. Values for the projected frontal area of the vehicles running on the local roads at present are proposed and results of an extensive CFD study are studied on the slip-streaming effects in various traffic conditions to quantify $K_{blockage}$ and the drag coefficient in the domestic tunnels.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.9
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• pp.681-685
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• 2013

A pilot-scale sand-box experiment was performed in order to investigate the effect of cross-flow velocity on the clogging of the filter sand in a model filtration pond. The clogging phenomenon was observed during the operation with the cross-flow varied in stages in a range of 0~40 cm/sec, and the experimental result was analyzed using a numerical code. Results showed that the cross-flow velocity in this range had no influence on the development of clogging and that clogging occurred mostly on the filter-surface. It was found that while the production rate decreased from $5m^3/m^2-day$ to $3m^3/m^2-day$ the clogging coefficient of the top 50 cm layer increased up to about 30,000 sec, which corresponded to 87% of the clogging coefficient of the total 2.4 m layer. Of the clogging coefficient of the top 50 cm layer, surface clogging constituted 90% while the other 10% was intermediate clogging. It was also found that the surface clogging increased while the intermediate clogging remained constant as the operation continued, and that filtrate turbidity along the filtration depth remained constant in spite of the increase in clogging.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.2
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• pp.120-131
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• 2011

A pilot-scale experiment of floodplain filtration with a filtration depth of 3.6m was performed employing flood/rest type raw-water supply system in an effort to find ways to improve river water quality by additional treatments of discharged effluent from sewage treatment plant. Soil samples were taken from 3 sites including Gumi, Daegu and Gimhae along the Nakdong river. Reductions of infiltration rates following increases in operating time was investigated in each soil sample, along with the analysis of removal efficiencies of various pollutants according to different depths and infiltration rates. The results show incremental development of clogging on the soil surface with increases in operation time, and illustrate exponential decrease in the infiltration rate. The time required for the removal of the clog from the soil surface was longer than 2 weeks for all soil samples analyzed. The stable infiltration rates for soils were 5 m/day for Gumi and for Daegu and Gimhae was 1 m/day. In unsaturated soils dissolved oxygen levels increased following the increase of filtration depth, suggesting that alternating application of flood and rest for raw-water supply effectively keeps the soil environment aerobic. For all soils, the nature of pollutant removal depending on the depth of filtration remained the same regardless of the infiltration rate. Most of the BOD and turbidity were removed within 1.2 m, about 30% of COD was removed within 3.6m and was expected to be removed further with increases in filtration depth. Nitrification occurred near the surface of all soils; however there was no significant removal of nitrogen in the filtration depths tested in this study. Although removal rate of phosphorus was low for Gumi's soil, it was high enough for other soils, suggesting that the method developed in this study could significantly improve river water quality.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.290-296
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• 2018

In this study, the cold test and the numerical analysis were carried out according to the shape parameters of the test model in order to confirm the operation range of high altitude environment simulation test facility for the supersonic vehicle. The blockage ratio, angle and length ratio were considered as the design parameters. The blockage rate is expected to be limited in the region of more than 40% due to the normal shock and expansion fan. It was confirmed that the angle of model should be selected at the size of 45 degrees or less due to the influence of the strong shock wave. There was no difference in performance between the lengths of 8 times the model diameter. Finally, we obtained the performance database according to the shape parameters of the conical test model and confirmed the operable range of the semi-freejet type high altitude environment simulation test facility.