• Investigative Magnetic Resonance Imaging
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• v.6 no.1
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• pp.41-46
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• 2002

The Fourier transform arteriography (FTA) exploits the periodic variation of arterial flow velociety of arterial flow velocity in stnchronized with cardiac cycles. This technique is intrinsically unique compared to other modern techniques. This technique separates the arteries from the veins using the pulsatile arterial flow without using the presaturation RF pulses. Therefore, it has less RF deposition and is free from the dark band artifacts that can arise from retrograde flow and curved arteries. Furthermore, it is free from the artifacts induced by eddy currents. However, there are some drawbacks such as a single projection view and the saturation of arteries at the end of an imaging slab. These drawbacks are circumvented by applying recently developed techniques. The fast gradient switching capability of modern MRI systems enabled us to incorporate dual projection views into the conventional FTA sequence without increasing the repetition time. In addition, signals from the distal arteries were enhanced by use of a ramped RF pulse and therefore the distal arteries were less saturated. By use of the FTA sequence with dual projection views and the ramped RF pulse, we acquired the sagittal and coronal projection views of femoral arteriograms simultaneously with more enhanced signals of distal arteries than the conventional FTA.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.23-29
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• 2006

In an annular injection supersonic ejector, the supersonic primary flow is injected along the side wall, therefore a funnel-shaped shock wave is generated by the contraction angle of the mixing chamber. In the present study, we developed a simple funnel shock wave model using 2-D wedge and conical shock wave relations. In result, the secondary flow pressure can be predicted more accurately than using a simple 2-D wedge shock wave model. Through the same analysis, the compression ratio and the adiabatic efficiency according to the entrainment ratio were calculated.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.3
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• pp.3-11
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• 2000

Purpose of this paper is to investigate the hood configuration at a tunnel entrance to reduce the micro pressure wave that is generated according to train speed. Two configurations were examined for the tunnel of 0.5 km in length. The experimental results show that a slit cover hood installed at the entrance of the tunnel reduces the maximum micro pressure wave by 41.2%, and the configuration with a slit cover hood installed at the entrance and the $45^{\circ}$ slanted portal at the exit of the tunnel suppress the pressure wave by 47.7%.

• Journal of the Speleological Society of Korea
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• v.25 no.26
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• pp.131-151
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• 1991

조사대상지역은 제주도 북제주군 한림읍 협재리 협재리국민학교 후편에 위치하고 있는 협재굴과 쌍룡굴, 황금굴, 그리고 양송이 재배장에서 망오름을 향해 2km 떨어진 곳으로 한림으로 나가는길과 교차하는 지점에서 서쪽으로 400-500m 떨어진 곳에 위치하고 있는 소천굴로서 협재굴과 쌍룡굴은 이미 개발되어 관광단지화 되어 있어 입구와 출구는 돌담과 축대를 쌓고 계단을 만들어 완전히 파괴해 버렸으므로 다른 동굴에서 볼 수 있는 동굴입구와 출구의 자연식물경관은 볼 수가 없었고 동백나무를 비롯한 수종의 상록활엽수와 도깨비고비등 수종의 양치식물은 인공적으로 이식해 놓은 실정이다. 황금굴과 소천굴은 아직은 개발이 되지 않고 사람의 접근을 통제하고 있었기 때문에 동굴입구에서 여러 종류의 상록활엽수와 양치식물을 볼 수 있었다. 한편 이들 동굴의 지표면은 인공적으로 조림한 곰솔이 대부분으로 인간간섭을 많이 받은 지역으로 지표면의 식물은 빈약하였다. 또한 이들 동굴의 지층은 표선리 현무암지대로 경사가 완만하며 평탄한 곳으로 이곳의 토양을 분석한 결과 토성은 유기물함량이 7.5%-17.4%로서 척박한 편이며 토양함수량은 9.8%-25.4%로 낮은 편이다.(중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.30-30
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• 1999

추진기관의 연소실과 같이 큰 열부하를 받는 경우 막냉각은 연소실을 보호하기 위해서 사용되는 대표적인 냉각기법이다. 막냉각의 성능을 극대화하기 위해서는 냉각유체를 2차원 슬롯을 통해서 분사시키는 것이 가장 효율적이지만 여러 가지 이유 때문에 실제 적용에 있어서는 슬롯입구 부근에 작은 구멍을 만들어 이로부터 분사되는 유체를 통해서 냉각시키게 된다. 본 연구에서는 주어진 덕트에서 분사율, 분사방법, 슬롯의 형상에 따른 슬롯 출구에서의 유동장 및 온도장 측정과 함께 물질전달 방법을 이용하여 슬롯 립(slot lip) 내벽에서 자세한 국소 열/물질전달계수를 구하였다. 분사율 0.5와 1.0에 대해서 주유동과 같은 방향으로 분사시켜줄 경우와, 유동을 제한시켜 주고 이차유동의 방향을 각각 주유동과 같은 방향과 반대방향으로 분사시키는 방법에 대하여 실험하였으며, 슬롯 입구에 경사슬롯을 설치하여 냉각유체를 분사시키는 방법에 대해서 실험하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.785-1-789-5
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• 2008

최근 수자원 분야에서는 대상유역의 최종출구점 뿐만 아니라 유역내 수문성분의 시 공간적인 분포특성에 관한 관심이 높아지고 있다. 이러한 분석을 위해 GIS와 연계된 물리적 기반의 분포형 수문모형이 널리 사용되고 있다. 하지만, 분포형 모형의 적용에 있어 문제로 제기되고 있는 격자크기에 대한 명확한 해법은 제시되지 못하고 있는 실정이다. 본 연구에서는 DEM 해상도(격자크기)에 따른 지형인자 및 수문성분의 변화를 검토하였다. 이를 위해 지형인자 도출에서 수문성분 분석까지 가능한 SWAT-K 모형을 횡성댐 상류유역에 적용하였다. 결과를 검토해보면, DEM 해상도가 낮아질수록, 최저고도는 증가, 최고고도는 감소, 따라서 평균고도는 다소 증가하는 경향을 보였다. 대상유역의 지형인자에 관계된 유역면적의 경우에는 해상도가 낮아질수록 다소 증가하였으며, 소유역별 유역평균경사의 경우에는 크게 감소하였다. 하도 지형인자의 경우, 해상도가 낮아질수록 주하도 길이는 감소, 주하도 경사는 반대로 증가하였다. 마지막으로 수문성분의 경우, DEM 해상도가 낮아질수록 유역 전체유출량은 다소 감소하였으며, 반대로 증발산량은 다소 증가하는 경향을 보였다. 유출성분을 세분하여 검토해보면, DEM 해상도가 낮아질수록 중간유출, 지하수유출의 경우 각각 크게 감소, 증가하는 경향을 보였다. 이는 DEM 해상도가 낮아질수록 유역경사가 완만해져 중간유출이 지하수유출로 유입되는 현상으로 파악된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.83-90
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• 1989

A runoff model was estabilished for the direct runoff hydrograph at each subareas by obtaining the storage coefficient based on stream magnitudes of geomorphic parameters. For this, the relationship between flowsection and channel distance from the outlet of each subareas was assumed as nonlinear equation, and compared with linear one. The applicability of the runoff model to the real watershed was tested for the Bochung river basin. The results of the analysis show that the model was approved to be used for the prediction of small watershed having no runoff records and a linear equation between flowsection and channel distance from the outlet of each subareas was more similar to the observed data for the upper subarea with a steep slope and small area, on the other hand, nonlinear equation for the lower subarea with mild slope and relatively large area.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.281-286
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• 2007

The Navier-Stokes equations are numerically solved for a two-dimensional small nozzle with the area ratio of 1.8 between the throat and the exit. The shock structures are verified inside the nozzle and near the exit varying with the pressure ratio and the length of the diverging part, respectively. Especially the irregular patterns in the pressure distribution near the throat are analyzed based on the geometric characteristics. It is found that there are similar phenomena in the shock wave structure between the pressure ratio and the length changes. Also there exists a normal shock just between two different oblique shocks crossing each other in special cases.

• Journal of the Korean Institute of Landscape Architecture
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• v.40 no.6
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• pp.161-172
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• 2012

The purpose of this study is to classify, evaluate and grade the existing highway tunnels to increase landscape and natural statistics keeping the structural safety about tunnel gates area and induce the ones that will be constructed in the future by drawing the improvements and restoring the techniques as an environment-friendly. To examine the types of tunnel gate area, total 54 tunnels were investigated by selecting Gyeongbu Expressway, Yeongdong Expressway, and Jungang Expressway. Tunnel entrances and exit ports were classified as a Wall-closed type and Protruding type, which is based on tunnel gate type. Vegetation Landscape types were classified as Multilayer-Same as the surrounding landscape_(MS), Multilayer-Difference of surrounding landscape_(MD), Single layer-Same as the surrounding landscape_(SS), Single layer-Difference of surrounding landscape_(SD), and a Desolate type which based on vegetation layers and environment-friendly. Potential vegetation recovery was identified based on the structural stability and revegetation potential of the tunnel. The factors include the structural stability of the slope height and slope gradient were selected. Revegetation potential was identified as a growth potential. This factor was used in the step to classify vegetation recovery potential of a tunnel. The result, which investigated the types of tunnel entrances and exit parts has found that the most typical in 33 places was a Wall closed type with 61.1% of the total ones. The case of vegetation landscape types was created but different from the ones surrounding it with 85.2% of the total ones. It is judged that the currently constructed vegetation of tunnel entrance and exit parts had put convenience on the safety and management before landscape consideration. In addition, tunnel entrance and exit parts with excellent potential for vegetation recovery were all Protruding type. In addition, it is judged that slope stability can easily obtain growth. Therefore, entrance and exist of the highway tunnels, which will be constructed in the future, should reflect location and the result of the natural and ecological survey in design by performing it in advance and their types, which minimize the damage area range, should be applied to the local characteristics suitably. In addition, the ecologically healthy tunnel construction should be done by introducing active vegetation recovery techniques based on its safety.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.968-969
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• 2011

The characteristics of second throat exhaust diffuser were investigated by using CFD. Because the second throat exhaust diffuser(STED) is known as the effective device for simulating high-altitude circumstance more than a cylindrical supersonic diffuser STED was analyzed. The back pressure around nozzle was reduced by entrance size of STED and it was observed that the initial strong shock was the weak oblique shock along the diffuser. Therefore the static pressure at nozzle exit was recovered as the ambient pressure and the STED worked well.