• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.479-486
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• 2011

In image-based CFD modeling of carotid bifurcation hemodynamics, it is often not possible (or at least not convenient) to impose measured velocity profiles at the common carotid artery inlet. Instead, fully-developed velocity profiles are usually imposed based on measured flow rates. However, some studies reported a pronounced influence of inflow boundary conditions that were based on actual velocity profiles measured by magnetic resonance imaging which showing the unusual presence of a high velocity band in the middle of the vessel during early diastole inconsistent with a Dean-type velocity profile. We demonstrated that those velocity profiles were induced by the presence of modest secondary curvature of the inlet and set about to test whether such more "realistic" velocity profiles might indeed have a more pronounced influence on the carotid bifurcation hemodynamics. We found that inlet boundary condition with axisymmetric fully-developed velocity profile(Womersley flow) is reasonable as long as sufficient CCA inlet length of realistic geometry is applied.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1269-1281
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• 1989

본 연구에서는 H를 고정하고 L을 변화시켜가며 내부의 유동구조가 어떻게 변하는가를 살펴보고, 특히 재부착이 일어나는 경우에는 급확대 부분만 존재하는 기존 실험결과와 비교분석하여 하류의 급축소부분이 전체 유동구조에 어떤 영향을 미치는가를 살펴보고자 한다. 실험에서 사용된 작동유체는 공기이며, 입구관 직경은 110mm, 급확대점과 급축소점사이의 연결부 직경은 220mm, 연결부의 길이는 L=300, 600 그리고 900mm의 3가지를 선택하였으며 기준속도는 입구관의 중심속도로 9.71 m/s이다. 입구직경(110mm)을 기준으로 한 Reynolds 수는 $R_{e}$=73,000 이고 입구관반경과 연결부반경의 차이인 계단높이(H=55mm)를 기준으로 하면 $R_{e=36}$ ,500이다. 연결부 의 급확대부분에서 입구관반경을 기준으로 한 반경확대비는 2이고 급축소부분의 반경 축소비는 1/2이다. 측정항목은 유동방향의 벽면압력분포, 유동방향의 평균속도분포 및 난류강도 등이며, L=900mm인 경우는 반경방향과 원주방향의 난류강도, Reynolds 전단응력도 측정되었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.10
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• pp.887-894
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• 2016

The CNG pressure vessel is manufactured by a deep drawing and ironing (D.D.I) process for forming cylinder parts, followed by a spinning process for formation of the dome part. However, studies on the buckling phenomenon of the dome part and formation of the inlet part have not been performed yet, and the CNG pressure vessel is produced by the experience of the field engineers and the trial and error method. In this study, buckling phenomenon during the spinning process was predicted by comparing critical buckling loads obtained through theoretical analysis with axial loads from the FEA, and a method for preventing buckling of the dome part was proposed by employing commercial software (Forge NxT 1.0.2). Also, to form the inlet part, forming loads of the roller at contact point between the roller and the dome part were analyzed according to radii of the dome part, and the inlet part was formed by controlling the radius of the dome part.

• The Journal of the Korea Contents Association
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• v.8 no.4
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• pp.92-99
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• 2008

Most of existing Ceramic bottle has a problem because of the entrance facing the upper, and then having the entrance exposed in the outside. This study has made up for this problem and manufactured a bottle having dual structure. This bottle contains the contents being poured, has the containing part having the entrance in the lower part, multiple connecting passage hole connected with the water containing part in the upper, and the storage part, keeping contents, located in the circumference of the water containing part. The tail end of the entrance of the water containing part is located more upper than the lower part of a storage part, being at the bottom. This bottle has a dual structure of which the entrance faces the lower part. So, because of checking a foreign substance to be inflowed, restraining the diffusion of an alcohol ingredient, it is possible to have the custody of products, having alcohol element, and other contents for a long time. And then, the water containing part, through the connecting hole, always can pour the contents of a certain level in a cup or bowl. Accordingly, the purpose of this study is to make a convenient, a practicable bottle with having settled problems of customary know-how explained previously.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.259-267
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• 2005

This paper analyzed characteristic of temperature change as well as bottom of tunnel with thermometer according to tunnel length and region during one year. And it measured temperature distribution near tunnel portal. In the paper it was known that tunnel entrance and exit have different characteristic temperature distribution in accordiance with bottom of tunnel per tunnel length. Temperature of tunnel changed from tunnel exit to fifty meter and distribution of tunnel temperature was established uniform regardless of tunnel length. But temperature distribution of tunnel changed in tunnel entrance differ from tunnel exit in the location of one hundred twenty five meter and one hundred fifty meter. Cold air inflowed from tunnel entrance have influenced with the location of one hundred twenty five meter and one hundred fifty meter.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.235-245
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• 2008

Since rapidly increase of tunnel with increasing of expressway, the study on safety improvement of safety device at entrance of expressway tunnels is necessary. The existence of tunnel occurs more speed reduction than an upward slope by itself, the collision accident of tunnel entrance causes heavier damage than that of general accident on the road. So, many kinds of safety devices such as poly-ethylene barrier, guard-rail are placed on the road side. But these devices affect the drivers as an obstacle. Although there are various safety devices that are placed at tunnel entrance, this study is related to following 2-cases. One is that the poly-ethylene barrier is placed and the other is that a safety devices is not placed. The reason that these two cases are selected, is that poly-ethylene barrier is usually placed at many tunnel entrances and safety devices can affect the drivers as an obstacle. This study is related to the difference of right-hand side clearance between inside tunnel and outside tunnel, too. The average difference observed car speed and VDS(vehicle detect system) speed nearby the tunnel is analysed. Through the statistical analysis of the average difference, this study suggests an alternatives on safety improvement of safety devices at entrance of expressway tunnels. It is concluded that the small difference of right-hand side clearance is desirable to drivers when a poly-ethylene barrier is placed. And when the difference of right-hand side clearance is large, no safety devices is desirable, and when the difference of right-hand side clearance is small, poly-ethylene barrier should be placed to improve safety.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.474-474
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• 2017

대하천 사업 이후 국내에서 경험하지 못한 대규모 다기능 보가 설치되었으며, 이로 인해 기존 하천에 서식하던 어류들의 군집, 이동 및 환경의 변화가 발생할 수 있으며, 산란을 위해 상류로 이동하거나 하류로 이동하려는 어류들에게는 상당히 큰 문제를 야기할 수 있다. 이러한 문제점들을 최소화하기 위해 다기능 보에는 대규모 어도가 설치되었으며, 다양한 흐름해석 모형을 이용하여 어도의 유인효율평가에 대한 연구가 이루어지고 있으나 이를 검증할 수 있는 실험적 연구는 부족한 실정이다. 어도의 유인효율평가에 있어 어도입구부 유속장 측정이 중요하다. 하지만 어도 입구부에 대한 접근성은 용이하지 못 할 뿐만 아니라, 기존에 사용하던 ADCP 장비로는 유속장 측정에 한계가 있다. 이를 극복하기 위해 드론영상을 활용한 LS-PIV기법과 GPS전자부자를 활용할 필요가 있다고 판단하였고, GPS전자부자를 어도 입구부에서 일정시간 유하시키는 동시에 드론영상촬영을 활용해 LS-PIV기법을 적용하여 유속을 측정하였다. 그 결과 LS-PIV기법을 적용한 실험이 주 흐름영역에서 안정적인 결과를 보였다. 본 실험 결과를 통해 새로운 유속 계측 방안을 보여줌으로써 접근성 및 안전성에 대한 효율적인 실험계측 방법을 제시하리라 사료된다.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.35-46
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• 1996

원심형 임펠러 내부 유로등 큰 곡률을 수반하는 터보기계 요소의 유동해석을 위한 계산코드를 개발하였다. 이 코드에서는 곡선좌표계에 유도된 3차원 비압축성 Navier-Stokes의 운동 방정식을 SMAC 음해법으로 푼다. 이 코드를 이용하여 유로의 단면이 정사각형이고 90도로 굽은 덕트내부의 층류 입구유동을 해석하고, 굽은 관 특유의 유동현상을 수치모사하였다 또한 곡관부 입구에서 충분히 발달한 유동, 또는 발달중인 유동이 유입될 경우에 이것이 곡관부 내부의 유동에 미치는 영향을 상·하류의 계산영역이 서로 다를 몇몇 유동장에 대하여 조사하고, 본 계산에서 얻어진 결과와 실형결과와의 비교로 본 3차원 유동해석 코드의 유효성을 검토 하였다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.7-10
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• 2009

터널 경계구역 내의 필수 조명기준은 가시기준, 즉 충분한 물체의 대비에 의해 결정된다. 본 연구에서는 터널도로를 대상으로 주간의 터널 입구부의 배경을 디지털 카메라로 측정하고, 그 이미지를 감지대비법의 일종인 광막휘도법(Veiling Luminance Method)과 기존 $20^{\circ}$ 시야의 L20법에 적용하여 터널의 경계부 평균휘도를 산출하였으며, 그 결과를 비교, 분석하였다.

• Korean Journal of Agricultural and Forest Meteorology
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• v.21 no.4
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• pp.250-260
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• 2019

This study assessed clove germination, shoot growth, photosynthesis and bulb development of southern-type garlic (Allium sativum L.) in a temperature gradient tunnel (TGT), to examine the impacts of increases in temperature on the growth of garlic and find a way to minimize them. The temperatures in the middle and outlet of the TGT were 3.2℃ and 5.8℃ higher, respectively, than the ambient temperature at the tunnel inlet. The germination of garlic cloves was late at temperatures of ambient+3℃ (in the middle of the TGT) and ambient+6℃ (at the outlet) than at ambient temperature (at the inlet). However, bolting and the timing of maximum leaf number per plant were faster at ambient+3℃ or +6℃ than at ambient temperature. Shoot growth was generally greater at ambient temperature. Bulb growth did not significantly differ according to cultivation temperatures, but fresh and dry weights were slightly higher at ambient temperature and ambient+3℃ in the late growth stage. The photosynthesis rate (A), stomatal conductance (g_s), and transpiration rate (E) were higher at ambient+3℃ than at ambient temperature. Furthermore, at ambient+3℃, the net photosynthetic rate (A_max) was high, while the dark respiration rate (R_d) was low. At ambient temperature and ambient+3℃, bulb development was healthier, resulting in better productivity and more commercial bulbs, while at ambient+6℃, the bulbs were small and secondary cloves developed, resulting in low commercial value. Therefore, at elevated temperatures caused by global warming, it is necessary to meet the low-temperature requirements before clove sowing, or to delay the sowing time, to improve germination rate and increase yield. The harvest should also be advanced to escape high-temperature stress in the bulb development stage.