• Journal of the Korean Society of Visualization
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• v.16 no.3
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• pp.8-15
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• 2018

Recently, as the high speed railway becomes more common, new environmental problems such as noise around tunnels are appearing. When a high speed train enters a tunnel, a compression wave in the tunnel is generated and propagated toward the tunnel exit at a sonic speed. When it reaches the tunnel exit, a part of compression wave radiates as a pulse typed impulse wave to the outside of tunnel. The impulse wave has an explosive noise. When the impulse wave is propagated around a village, it induces a serious noise or other problems to the resident. In order to solve these engineering problems, it is important to investigate the radiation characteristics of the impulse wave radiated from the tunnel exit. In this study, the effect of the length and angle of the baffle plate at the tunnel exit on the impulse wave radiated from the tunnel exit was investigated by numerical analysis. As a results, the baffle plate greatly affected the propagation of impulse wave.

• Journal of the Korean Society of Tobacco Science
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• v.18 no.1
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• pp.92-99
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• 1996

A mathematical model of the pressure gradient of supercritical CO2 in a vertical tobacco bed was developed in this study. In particular, the compaction of the tobacco as a function of temperature and CO2 flow is included in the model. Downflow of CO2 (low condition is described. At velocities in excess of 0.6 cm/sec at 7$0^{\circ}C$, there is a large increase in pressure gradient for beds deeper than about 0.5 m. The proposed model offers a better understanding of operating the process using supercritical CO2.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.29-29
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• 2000

가스터빈 엔진의 성능을 제대로 예측하기 위해서는 먼저 주요 구성품인 압축기, 터빈 등의 성능 자료가 충분히 알려져 있어야 한다. 특히 압축기는 조건의 변화에 따라 성능변화가 크므로 엔진 성능예측시 압축기 성능특성은 매우 중요한 요소라 할 수 있다. 압축기의 경우, 유동의 특성상 역압력 구배로 인한 유동의 박리가 발생하는 등 유동현상이 매우 복잡해진다. 이와 같은 2차원 압축기 익력 성능예측을 위하여 압축성, 비압축성 수치해석기법 및 난류 모델을 DCA(doble circular arc) 아음속 압축기 익렬에 적용하여 실험 결과와 비교 검토하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.171-176
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• 2008

Active suspension controls stiffness and damping between unsprung mass and sprung mass in order to increase the ride quality. However, to increase the riding quality, the handling quality should be decreased and the rattle space should be increased. So, active suspension should cope with these conflict conditions. Therefore its actuating devices have to produce sufficient actuating force and have sufficiently short response time. In this paper, the dynamic characteristics of 1/4 car model with an active suspension is studied according to hydraulic design variables. The active suspension consists of a hydraulic servo valve and a hydraulic cylinder. It shows better performance when it has more powerful and faster actuator.

• Journal of computational fluids engineering
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• v.2 no.2
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• pp.1-8
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• 1997

Two versions of anisotropic k-ε turbulence model are incorporated in the modified k-ε model of Sohn et al. to avoid the need for the experimental normal stress value in the model and applied to convergent and divergent flows with strong and adverse pressure gradients in the plane of symmetry of a body of revolution. The models are the nonlinear k-ε model of Speziale and the anisotropic model of Nisizima & Yoshizawa. All of the models yield satisfactory results for relatively complex flow on a plane-of-symmetry boundary layer. The results of the models are compared with those results of experimental normal stress value.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1915-1918
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• 2003

Atherosclerosis, which is a degenerate disease, is believed to occur in the vascular system due to deposition of cholesterol and low density lipoprotein(LDL) or thrombosis on the blood vessel. Atherosclerosis narrows arterial lumen, which is known as stenosis phenomenon of blood vessel. Pathogenesis of atherosclerosis is thought to occur mainly by aging. Restenosis phenomenon is observed in the same site of insertion of a stent and balloon angioplasty after treatment of interventional theraphy. Several hypothetical theories related to the generation of atherosclerosis have been reported: high shear stress theory, low shear stress theory, high shear stress gradient theory, flow separation and turbulence theory and high pressure theory. However, no one theory clearly explains the causes of atherosclerosis. In the present study the generation of atherosclerosis in the left coronary artery is investigated. The hypotheses are verified by using the computer simulation.

• Proceedings of the Membrane Society of Korea Conference
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• 1994.10a
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• pp.46-55
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• 1994

오늘날 막분리공정의 응용은 다른 분리공정에 비해 경제성과 편리성으로 비교우위에 있어 점차로 사용규모면에 있어서 증대되고 있다. 예를 들면, 바닷물을 음용수로 전환하거나 식품이나 의약공업에서 고분자화합물을 정제, 농축, 분리할 뿐만아니라 신장에서 불순물을 제거에 이르기까지 확대발전되어오고 있으며 화공약품의 분리회수, 초순수화나 환경산업의 폐수처리, 가스의 분리와 회수등의 응용에 이르기까지 쓰임새가 다양하며, 앞으로의 응용범위는 새로운 기능의 분리막개발과 함께 점점 확대되고 있다. 이와같은 막분리공정상 물질전달의 기본적특성인 추진력과 물리적인 성질의 중요성을 이해하는 것은 막분리공정을 설계제작하는데 필요하다. 막내에서 물질전달은 분리코져하는 물질의 확산, 전기장에의한 대류속도, 농도, 압력, 흡착 그리고 온도구배 등 물질이동현상을 조절하는 인자들 뿐만아니라 막의 물리적, 화학적 특성과 분리대상물질의 물리화학적 특성등에 의해 결정된다. 이러한 막내에서의 추진력들은 서로 상호 보완적이고 경우에 따라서는 새로운 효과를 나타낼 수 있다. 본 논문에서는 추진력에 따른 막물질이동에 영향을 주는 요소들을 저자가 경험한 결과들을 토대로 총론형식으로 열거하였다.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.571-575
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• 2016

두꺼운 에어포일은 받음각이 클 때 역압력 구배가 일어날 수 있기 때문에 날개의 중앙부 후방에서 유동박리(Flow separation)와 와류 진동(Vortex shedding)이 쉽게 발생할 수 있다고 알려져 있다. 항공기가 이 착륙할 때 받음각이 커짐에 따라 유동박리에 의한 실속이 발생할 수 있는데 이를 지연 시켜 실속각을 크게 하면 안전성이나 효율 면에서 유리하다. 이를 위해 날개에 Hole을 만들어 와류를 잡아 유동의 박리를 지연시키고자 하였다. 본 연구에서는 EDISON_CFD 시스템의 2D_Incomp_P 솔버를 사용하여 NACA0018 에어포일의 윗면에 다른 위치의 Hole이 있을 때와 크기가 다른 Hole이 있을 때의 실속각이 가장 커지는 경우를 찾아보았다. Hole의 위치와 반지름 크기를 변화시켰을 때 각각의 최대 양력 계수를 비교하여 실속각의 증가와 Streamline을 그려 유동박리가 지연됨을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.4
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• pp.453-460
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• 2005

Experiments were conducted to investigate the effect of the surface roughness on the flat plate turbulent boundary layer. The square rods were installed at the leading edge to make surface roughness. The particle image velocimetry was used to measure the mean velocities and velocity fluctuation component. All measurements were made over a range of w/k=1. 2 5 and $Re_x=80.000{\sim}360,000$. Friction velocity was measured by using Clauser plot method. The level of turbulent intensities on roughness surface appears more strongly than that of turbulent intensities on flat plate. A correlation of boundary layer thickness in term of $Re_x$ and w/k are presented.

• Journal of the Korean Society of Visualization
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• v.20 no.1
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• pp.38-44
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• 2022

An interscale transport of the turbulent kinetic energy (TKE) and Reynolds shear stress (RSS) is examined in an adverse pressure gradient (APG) turbulent boundary layer (TBL). The direct numerical simulation data of an APG TBL at Re_τ = 834 and β = 1.45 is employed. The TKE and RSS transport equations are divided into large and small scales, leading to the introduction of interscale transport. The TKE mainly transfers from large scales to small ones in the outer region, and vice versa for the RSS. An interscale transport of TKE and inverse interscale transport of RSS are amplified by APG, and the latter results in the increase in large scales of TKE production. Some of outer large scales of enhanced TKE transfer to small scales and then dissipate by viscosity, and the remains dissipate turbulent-non-turbulent interfaces by turbulent transport.