• 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.

• 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.

• Journal of the Korean Society for Railway
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• v.12 no.4
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• pp.457-464
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• 2009

The now velocity distribution at inlet of diesel Particulate filter (DPF) which is connected to each curved duct was simulated using $STAR-CD^{(R)}$. Three kinds of models which describe the shapes of the curved duct ware used for the CFD simulation. The simulation results were compared with the experimental data of velocity distribution which was obtained using a Pitot tube and 2-D positioning machine. At the $90^{\circ}$ curved connecting condition, the CFD simulation results of flow velocity distribution at inlet of the DPF showed a horse hoop shape shifted from the axial center line of the DPF. The CFD simulation results agree reasonably with those of the experiments.

• Applied Microscopy
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• v.40 no.4
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• pp.237-244
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• 2010

Utricularia forms small, but complex carnivorous trap along the stem either in water or in soil depending upon species. The shapes and sizes of the traps, appendages, and trichomes are known to differ among aquatic, terrestrial and epiphytic species. In the present study, the morphology and microstructure of the trap in aquatic Utricularia japonica and terrestrial U. livida were examined using light and electron microscopy. The aim of this study was to compare the characteristics of trap features between the aquatic and terrestrial species. The trap was found to be comprised of a thin walled bladder with numerous capitate trichomes, two-armed bifid and four-armed quadrifid glands in both species; however, the traps of the two species were different in size, and number and morphology of the trichomes and glands. Aquatic Utricularia was chlorenchymatous with chloroplasts distributed throughout the body, whereas the terrestrial species was translucent without plastids due to an adaptation to underground habitats. Furthermore, the former differed considerably in that the traps developed antenna and appendages around the entrance area. A peculiar trap entrance was also noted in U. livida, which exhibited radiating rows of various trichomes within funnel-shaped tissue. A large number of glandular trichomes covered the entrance area and door surface with four trigger hairs each in the aquatic form but only two in the terrestrial form. The glandular trichomes near the door secreted a large amount of mucilage that temporarily composed the velum in the U. japonica, however, it was not observed in the terrestrial species. All of the aforementioned features were highly related in their structure and function during carnivorous mechanism in Utricularia. The current findings provide important data for further comparison of the different life forms within Utricularia.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.11
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• pp.965-973
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• 2010

Numerical analysis has been carried out to investigate the heat transfer characteristics of a plate heat exchanger. The multi-cell models with inlet part and outlet part are used for performing numerical simulation. The plate heat exchanger is characterized by chevron angle of $15^{\circ}$, corrugation pitch of 24mm and corrugation height 6~12mm. The length of the inlet-part considered in the analysis ranges from 24.8 to 124mm and Reynolds numbers range from 1,000 to 10,000. The correlations such as friction factor and Colburn factor are compared with previous experimental data. The results can be utilized for designing the plate heat exchanger.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2007.05a
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• pp.149-156
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• 2007

부산의 대표적 큰 계곡인 성지곡수원지는 남쪽으로 부산의 최대 도심인 서면을 향해 열려 있고, 그 이외의 삼면은 높은 산지로 둘러싸여 있다. 그래서 성지곡-서면-남항 일대는 낮에는 해풍이 곡풍(남풍)의 형태로 불고, 야간에는 산풍이 육풍(북풍)의 형태로 불고 있다. 이렇게 형성된 국지풍 순환의 규모와 특성을 평가하기 위하여, 계곡 입구와 도심인 서면 부근에 자동기상관측장치를 설치하여 특별 관측을 수행하였다. 관측결과 주간에는 서면 부근의 기온이 성지곡 입구보다 낮았고, 야간에는 이와 반대로 나타났으며 그 차이는 대체로 $3^{\circ}C$ 내외였다. 이것은 주로 지표면 가열의 의한 기단변질의 결과로 판단된다. 관측 일에 확인된 도로표면온도는 낮에 약 65도까지 상승하였으며 야간에도 30도 정도의 고온이 유지되었다. 이 연구에서는 현장관측으로 확인된 기단변질과정을 이해하기 위하여 2차원 대류모델을 이용한 수치실험을 수행하였다. 수치실험의 결과 낮에는 지표로부터 약 $150W/m^2$이상의 현열이 보급됨이 확인되었다. 야간에도 $10W/m^2$ 내외의 현열이 대기 중으로 보급되어 성지곡 수원지에서 발원된 냉기류를 가열시키고 있음이 확인되었다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.4
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• pp.348-354
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• 1987

The behavior of crab, Charybdis japonica h. Milne EDWARDS, to the net pots with baits was investigated alternately in the experimental tanks. One of the pots being dropped on the tank bottom, the crabs touched it to obtain the bait probably reacted by their senses of smell and sight, and increased gradually in the number of touch to show a maximum within 30 min. The crabs, if touched circular pots, were guided more easily to the pot entrances than the case of touching square ones, but the guidance from the vicinity of the entrances into the pots was easier in the square. When the crabs entered the pots, they always showed a sharp precaution. However, most of enterings were made mainly within 30 minutes and easier in pots with lower entrances. If 30 min. elapsed, the entering was little made by the decrease in the number of touch and the getting-out was remarkable, especially in pots with low entrances. But, in all the pots the getting-out was hampered by the drawing of the entrance tips into the pots. In case in which flappers were attached to the entrance tips, the entering was very hampered, hut the getting-out was not shown.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.95-105
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• 2014

The CUPID code has been developed for a transient, three-dimensional, two-phase flow analysis at a component scale. It has been validated against a wide range of two-phase flow experiments. Especially, to assess its applicability to single- and two-phase flow analyses in the Calandria vessel of a CANDU nuclear reactor, it was validated using the experimental data of the 1/4-scaled facility of a Calandria vessel at the STERN laboratory. In this study, a preliminary thermal-hydraulic analysis of the CANDU reactor moderator tank using the CUPID code is carried out, which is based on the results of the previous studies. The complicated internal structure of the Calandria vessel and the inlet nozzle was modeled in a simplified manner by using a porous media approach. One of the most important factors in the analysis was found to be the modeling of the tank inlet nozzle. A calculation with a simple inlet nozzle modeling resulted in thermal stratification by buoyance, leading to a boiling from the top of the Calandria tank. This is not realistic at all and may occur due to the lack of inlet flow momentum. To improve this, a new nozzle modeling was used, which can preserve both mass flow and momentum flow at the inlet nozzle. This resulted in a realistic temperature distribution in the tank. In conclusion, it was shown that the CUPID code is applicable to thermal-hydraulic analysis of the CANDU reactor moderator tank using the cost-effective porous media approach and that the inlet nozzle modeling is very important for the flow analysis in the tank.

• Clean Technology
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• v.25 no.4
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• pp.324-330
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• 2019

The selective catalytic reduction system is a highly effective technique for the denitrification of the flue gases emitted from the industrial facilities. The distribution of mixing ratio between ammonia and nitrogen oxide at the inlet of the catalyst layers is important to the efficiency of the de-NOx process. In this study, computational analysis tools have been applied to improve the uniformity of NH₃/NO molar ratio by controlling the flow rate of the ammonia injection nozzles according to the distribution pattern of the nitrogen oxide in the inlet flue gas. The root mean square of NH₃/NO molar ratio was chosen as the optimization parameter while the design of experiment was used as the base of the optimization algorithm. As the inlet conditions, four (4) types of flow pattern were simulated; i.e. uniform, parabolic, upper-skewed, and random. The flow rate of the eight nozzles installed in the ammonia injection grid was adjusted to the inlet conditions. In order to solve the two-dimensional, steady, incompressible, and viscous flow fields, the commercial software ANSYS-FLUENT was used with the k-𝜖 turbulence model. The results showed that the improvement of the uniformity ranged between 9.58% and 80.0% according to the inlet flow pattern of the flue gas.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.109-117
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• 2015

Aircraft needs an inlet duct to supply the airflow to engine face. A fighter aircraft that requires low radar observability has to hide the engine face in the fuselage to reduce the Radar Cross Section(RCS). Therefore, the flow path of the inlet duct is changed into S-shape. The performance of the aircraft engine is known to be influenced by the shape and the centerline curvature of the S-Duct. In this study, CFD analysis of the RAE M 2129 S-Duct has been performed to investigate the influence of aspect ratio of inlet geometry. The performance of the S-Duct is evaluated in terms of the distortion coefficient. To simulate the flow under adverse pressure gradient better, $k-{\omega}SST$ turbulence model is employed. The computational results are validated with the ARA experimental data. The secondary flow and the flow separation are observed for all computational cases, while the semi-circular geometry has been found to produce the best results.