• Journal of the Korean Society of Radiology
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• v.83 no.4
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• pp.945-950
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• 2022

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a common autoimmune encephalitis that is noted to be a severe but treatable disease entity. Patients with anti-NMDAR encephalitis often develop psychotic symptoms, including delusions, hallucinations, and paranoia, as well as memory impairment and persistent loss of attention. However, MRI findings in such patients show no abnormalities in most cases. Although typical brain abnormality features, known as T2 hyperintensities, involve the brain parenchyma and contrast enhancement at the cerebral cortex or overlying meninges, isolated leptomeningeal enhancement has been rarely reported in anti-NMDAR encephalitis. Herein, we report a patient with anti-NMDAR encephalitis who presented with isolated leptomeningeal enhancement, additionally showing the diagnostic value of contrast-enhanced fluid-attenuated inversion recovery imaging.

• Proceedings of the KIEE Conference
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• 2008.04a
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• pp.189-190
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• 2008

원자력발전소의 탈기기 계통(Gas Stripper System)은 약 $25^{\circ}C$의 순수를 1.2기압, $105^{\circ}C$ 상태를 거쳐서 가스가 없는 상태(탈기)로 만들어 주는 계통이다. 탈기 상태를 유지하면서 지속적으로 순수를 만들기 위해서 본 계통에는 수위와 압력 제어루프가 있다. 탈기 상태에서는 탈기기 탱크내의 유체 상태가 이상(Two Phase)이기 차가운 급수를 사용한 수위와 압력 제어가 어렵다. 본 논문에서는 모델 기반으로 제어 최적화를 하기 위하여 제어 구성 요소들에 대한 제어 모델링 및 검증 과정을 기술한다. 제어모델링은 일반적으로 Parameter Identification 기법을 적용하지만, 유체역학 수식 모델, 운전 데이터, 탱크와 배관의 설계 자료 등을 이용한 경험적 방법을 적용하였으며 운전 데이터를 사용하여 검증하였다.

• Journal of the Korean Solar Energy Society
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• v.25 no.1
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• pp.87-96
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• 2005

본 논문은 압력차로 인한 유체의 유동장에서 서스펜션의 입자 밀도를 분포 규명하기 위해 적용할 수 있는 Electric Impedance Tomography (EIT)의 새로운 기법에 대한 효율성을 다루고 있다. Regularized Newton-Raphson iterative method를 근간으로 inverse problem의 해를 구하는데, 이는 곧 목적 함수(object function)를 몇 가지의 제한조건(constraints) 하에서 최소화시키는 과정이라 할 수 있다. 한편, 관련 forward problem은 유한요소법(FEM)을 이용하여 해결하며, 기존의 연구와는 달리 선형 형상 함수(linear shape function)를 이용하여 전도도가 연속적인 물성치로 유동장에 분포되어 있는 것으로 가정하였다. 여러 경우의 test run에 대한 결과는 본 논문에서 적용한 방법론의 타당성을 보여 주고 있다. 태양에너지의 추출을 위해 직접촉식 열교환기가 종종 이용되고 있는데, 본 연구는 열교환기 내부의 분산 유체에 대한 해석에 일조를 할 수 있을 것으로 기대된다.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.1-10
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• 2011

A new computational program, which is based on the CIP/CCUP(Constraint Interpolation Profile/CIP Combined Unified Procedure) method, has been developed to numerically analyse sloshing phenomena dealt as multiphase-flow problems. For the convection terms of Navier-Stokes equations, the RCIP(Rational function CIP) method was adopted and the THINC-WLIC(Tangent of Hyperbola for Interface Capturing-Weighted Line Interface Calculation) method was used to capture the air/water interface. To validate the present numerical method, two-dimensional dam-breaking and sloshing problems in a rectangular tank were solved by the developed method in a stationary Cartesian grid system. In the case of sloshing problems, simulations by using a improved MPS(Moving Particle Simulation) method, which is named as PNU-MPS(Pusan National University-MPS), were also carried out. The computational results are compared with those of experiments and most of the comparisons are reasonably good.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.61-66
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• 2015

In this study, an aero-acoustic analysis around pantograph of a high speed train is performed. Computational technique and grid system is validated with wind tunnel test result and unsteady acoustic pressure data are used for analyzing noise level of each part of pantograph. FLUENT is used for flow analysis and LES(Large Eddy Simulation) is applied for analyzing turbulent flow. For acoustic analysis, Ffowcs Williams-Hawkings(FW-H) acoustics model is used and it bring the aero-acoustic characteristic of pantograph. As the result, contact strip, knee, substructure of pantograph is confirmed as a main source of aero-acoustic noise and it is dealt in various frequencies. The result is expected to help building improved grid system.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.5-10
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• 2014

In this paper, the experimental study was carried to investigate the effect of angle of the anti-vortex holes on the film cooling effectiveness on a flat plate. The pressure sensitive paint technique was applied to measure the film cooling effectiveness. Two anti-vortex hole angles of $0^{\circ}$ and $15^{\circ}$ with respect to the primary hole were considered, and the simple cylindrical hole case was also tested. The blowing ratio based on the cylindrical hole was 0.5 and the same flow rate was kept for all anti-vortex hole cases. Results showed that the film cooling effectiveness for the anti-vortex hole cases were much higher than that of the cylindrical case. Among the anti-vortex hole cases, $15^{\circ}$ angle anti-vortex hole case showed higher film cooling effectiveness than that by the $0^{\circ}$ angle anti-vortex hole case.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.154.2-154.2
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• 2010

상대적으로 이산화탄소 배출량이 적으며, 기존의 천연가스를 대체할 수 있고, 21세기 신 에너지원으로 기대되고 있는 메탄 하이드레이트(Methane hydrate)는 태평양과 대서양의 대륙사면 및 대륙붕, 남극대륙의 주변해역 등지에서 자연적으로 발생한 메탄 하이드레이트의 분포가 확인되었으며, 그 매장량의 1조 탄소톤 이상으로 기존 화석연료의 매장량이 5천억 탄소톤, 대기중의 메탄가스가 3억 6천만 탄소톤임을 고려할 때 2배에 이르는 막대한 양이라고 보고하였다. 따라서 메탄 하이드레이트는 화석에너지를 대체할 수 있는 차세대 청정 에너지 또는 대체 에너지원으로서의 무한한 잠재력을 가지고 있어 새로운 에너지분야로 크게 주목을 받고 있다. 또한 하이드레이트는 $172m^3$의 메탄가스와 $0.8m^3$의 물로 분해된다. 만약, 특성을 역으로 이용하여 산업적으로 고체화 수송을 할 경우 화수송보다 18-24%의 비용절감이 이루어질 것으로 예상되어진다. 그러나 메탄 하이드레이트를 인공적으로 만들경우 물과 가스의 반응율이 낮아 하이드레이트 형성시간이 상당히 길고 가스 충진율도 낮다. 따라서 본 연구에서는 하이드레이트를 빨리 만들며 가스 충진율도 증가시키기 위하여 증류수와 다공성물질이며 나노세공(Nano pore)을 가지고 있는 제올라이트를 증류수에 첨가하고, 초음파 분산하여 만든 혼합유체를 메탄가스와 반응시켜 하이드레이트 형성 실험을 수행하여 비교 분석하였다. 그 결과 0.01 wt% 제올라이트 혼합유체에서 증류수보다 하이드레이트가 훨씬 빨리 생성되었으며, 메탄가스소모량은 ${\Delta}T_{subc}$=0.5K에서 약 4배 높음을 보였다.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.3
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• pp.185-189
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• 2017

Recently, titanium alloys have been widely used in aerospace, biomedical engineering, and military industries due to their high strength to weight ratio and corrosion resistance. However, it is well known that titanium alloys are difficult-to-cut materials because of a poor machinability characteristic caused by low thermal conductivity, chemical reactivity with all tool materials at high temperature, and high hardness. To improve the machinability of titanium alloys, cryogenic cooling with LN2 (Liquid Nitrogen) and nanofluid MQL (Minimum Quantity Lubrication) technologies have been studied while turning a Ti-6Al-4V alloy. For the analysis of turning process characteristics, the cutting force, the coefficient of friction, and the surface roughness are measured and analyzed according to varying lubrication and cooling conditions. The experimental results show that combined cryogenic cooling and nanofluid MQL significantly reduces the cutting forces, coefficients of friction and surface roughness when compared to wet condition during the turning process of Ti-6Al-4V.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.166-173
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• 2007

Collision analysis problems between ship to ship can be generally classified into the external mechanics(outer dynamics) and internal mechanics(inner dynamics). The former can be also dealt with the concept of fluid-structure interaction and the use of rigid body dynamic program, depending on the ways handling the hydrodynamic pressure due to surrounding water. In this study, full scale ship collision simulation was carried out, such as a DWT 75,000 ton striking ship collided at right angle to the middle of a DWT 150,000 struck ship with 10 knots velocity, coupling MCOL, a rigid body mechanics program for modeling the dynamics of ships, to hydrocode LS-DYNA. It could be confirmed that more suitable damage estimation would be performed in the case of the collision simulations with consideration of surrounding water through the comparison with the collision simulation results of fixed struck ships without it. Through this study, the opportunity could be obtained to establish a more effective ship collision simulation technique between ship to ship.

• The KSFM Journal of Fluid Machinery
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• v.12 no.1
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• pp.35-42
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• 2009

The flow and heat/mass transfer characteristics on the squealer tip surface of a high-turning turbine rotor blade have been investigated at a Reynolds number of $2.09{\times}10^5$, by employing the oil-film flow visualization and naphthalene sublimation technique. The squealer rim height-to-chord ratio and tip gap height-to-chord ratio are fixed as typical values of $h_{st}/c$ = 5.5% and h/c = 2.0%, respectively, for turbulence intensities of Tu = 0.3% and 15%. The results show that the near-wall flow phenomena within the cavity of the squealer tip are totally different from those over the plane tip. There are complicated backward flows from the suction side to the pressure side near the cavity floor, in contrast to the plane tip gap flows moving toward the suction side after flow separation/reattachment. The squealer tip provides a significant reduction in tip surface thermal load with less severe gradient compared to the plane tip. In this study, the tip surface is divided into six different regions, and transport phenomena at each region are discussed in detail. The mean thermal load averaged over the squealer cavity floor is augmented by 7.5 percents under the high inlet turbulence level.