• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.04a
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• pp.15-15
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• 1998

The problem of the impingement of a sonic or a supersonic jet on a flat surface has not only wide applications but has also interesting and very complex flow phenomena. The main applications of this impinging jet include prediction of solid surface erosion, design of launcher systems, stage separation of multi-stage rocket system, V/STOL operations, thermal spray system, and manufacturing technologies of materials. Much have been learned about the supersonic impinging jet flow field but many fundamental questions have not been answered satisfactorily. The problem encompasses many facets of fluid dynamics which, in combination, present the compressibility effect and the viscous-inviscid interaction, coupled with flow separation and reattachment. What is more, there are many flow parameters that have on the impinging jet flow field, for example, Mach number, Reynolds number, pressure ratio, distance between the nozzle exit and flat plate, jet shock structure, nozzle diameter and etc. Thus the existing data on the supersonic impinging jet flow present considerable disagreement in which quantitative comparison between one result and another is often impossible.

• Proceedings of the KAIS Fall Conference
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• 2008.05a
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• pp.43-45
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• 2008

박막 제작공정은 반도체 제작 공정, 고정밀도의 하드디스크 및 레이저 디스크 기술, LCD/P에 DML평판 디스크 플레이어 제작 공정에 있어 중요한 기술이다. 더욱이, 이 공정은 이동 전화 커버의 증착 및 전자 차폐의 일반기술, 램프의 반사판, 화장품 용기, 몇몇 상품에 있어 카메라 렌즈의 광학 표면 코팅과 코팅 필름 제작에 사용된다. 본 연구의 주요목적은 반도체 제작 공정과 많은 산업 분야에서 기본 재료로 사용되는 전영저항의 개발에 있다. 개발 공정은 다음과 같다. 전자빔이 최상의 진공 분위기에서 텅스텐 필라멘트의 열에 의해 방출된다. 그때 전자는 높은 전압에서 가속화된다. 전자들은 반대 재료에 충돌되고, 반대편 재료는 발생 열에 의해 코팅된다. 1차년도 연구목적은 고성능 전열 저항체 개발을 위한 지름 당 필라멘트 선의 기계적 특성을 조사하고 CAE 해석을 수행하며, 2차 년도에는 대량 생산 라인 구축을 위한 자동검사 라인 개발에 초점이 맞추어져 있다. 만일, 본 연구를 통해 전열 저항체가 개발된다면, 그 제품은 고효율, 외국제품 대비 가격 경쟁력을 가지므로 제품 경쟁력을 가질 수 있을 것으로 생각된다.

• Journal of the Korean Society of Visualization
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• v.16 no.3
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• pp.16-25
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• 2018

PIV experiments were carried out to visualize the velocity distribution of the sweeping jet impinging onto a flat plate and kinematic behavior of the jet from the fluidic oscillator. Two parameters such as four different Re cases and four different jet-to-wall distances were examined. Time-resolved two dimensional PIV measurements were performed for both streamwise and normal planes respect to the jet axis. Ensemble averaged and phase averaged velocity fields were obtained for the tested range of parameters. The sweeping frequency of the jet increases linearly with increase of Re. The kinetic energy of the sweeping jet decreases as the distance from the jet to the impinging plate increases. In addition, turbulence flow is generated due to the swinging motion of sweeping jet, and various vortices such as primary and secondary vortex are observed near the impinging wall.

• Journal of the Korean Vacuum Society
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• v.18 no.6
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• pp.426-434
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• 2009

A global simulation of $SiH_4/H_2$ discharge is conducted in a planar-type inductively coupled plasma (ICP) discharge. We numerically solve a set of spatially averaged fluid equations for electrons, positive ions, negative ions, neutrals, and radicals. Absorbed power by electrons is determined by an analytic electron heating theory including the anomalous skin effect. Also, we investigate functional dependence of various discharge quantities such as the densities of various species and the temperature of electron on external controllable parameters such as ratio between $SiH_4$ and $H_2$, power and pressure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.1
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• pp.37-44
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• 2019

A bond-based peridynamic model has been reported dynamic fracture characteristic of brittle materials through a simple constitutive model. In the model, each bond is assumed to be a simple spring operating independently. As a result, this simple bond interaction modeling restricts the material behavior having a fixed Poisson's ratio of 1/4 and not being capable of expressing shear deformation. We consider a state-based peridynamics as a generalized peridynamic model. Constitutive models in the state-based peridynamics are corresponding to those in continuum theory. In state-based peridynamics, thus, the response of a material particle depends collectively on deformation of all bonds connected to other particles. So, a state-based peridynamic theory can represent the volume and shear changes of the material. In this paper, the perfect plasticity is considered to express plastic deformation of material by the state-based peridynamic constitutive model with perfect plastic flow rule. The elastic-plastic behavior of the material is verified through the stress-strain curves of the flat plate example. Furthermore, we simulate the high-speed impact on 3D granite model with a nonlocal contact modeling. It is observed that the damage patterns obtained by peridynamics are similar to experimental observations.

• Journal of Energy Engineering
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• v.10 no.3
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• pp.272-277
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• 2001

An experimental study of jet impinging the non-isothermal heating surface with linear temperature gradient is conducted with the presentation of the turbulent flow characteristics and the heat transfer rate, represented by the Nusselt number. The jet Reynolds number ranges from 15,000 to 30,000, the temperature gradient of the plate is 2~4.2$^{\circ}C$/cm and the dimensionless nozzle to plate distance (H/D) is from 2 to 10. The results show that the peak of heat transfer rate occurs at the stagnation point, and the heat transfer rate decreases as the radial distance from the stagnation point increases. A remarkable feature of the heat transfer rate is the existence of the second peak. This is due to the turbulent development of the wall jet. Maximum heat transfer rate occurs when the axial distance from the nozzle to nozzle diameter (H/D) is 6 or 8. The heat transfer rate can be correlated as a power function of Prandtl number, Reynolds number, the dimensionless nozzle to plate distance (H/D) and temperature gradient (dT/dr). It has been found that the heat transfer rate increases with increasing turbulent intensity. The wall jet is influenced by temperature gradient and the effect becomes more important at higher radii.

• Solar Energy
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• v.15 no.1
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• pp.85-94
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• 1995

This research has been proceeded over the potential core region(H/B=2) of two-dimensional impinging air jet sytem, in which square rods(width of 6 mm) has been set up in front of heating surface in order to increase heat transfer. The objective of this research was to investigate the characteristics of heat transfer and air flow, in eases of the clearance from rods to heating surface(C=1, 2, 4, 6 mm) and the pitch between each rods(P=30, 40, 50 mm) changed. And this research compared the above with the experimentation without rods. As result, heat transfer performance was best under the condition of C=1mm, in case clearance changed, and there was no serious difference in the effect of heat transfer augmentation in the case of pitch of rods changed.

• Journal of computational fluids engineering
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• v.6 no.3
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• pp.32-40
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• 2001

Viscous solutions of supersonic jet impinging on a flat plate normal to the flow are simulated using three-dimensional Navier-Stokes solver. The jet impinging flow structure exhibits such complex nature as shock shell, plate shock and Mach disk depending on the flow parameters. Among others, the dominant parameters are the ratio of the nozzle exit pressure to the ambient pressure and the distance between the nozzle exit plane and the impinging plane. In the present study, the nozzle contour and the pressure ratio are held fixed, while the jet impinging distance is varied to illuminate the characteristics of the jet plume with the distance. As the plate is placed close to the nozzle at 3D high, the computed wall pressure at or near the jet center oscillates with large amplitude with respect to the mean value. Here D is the nozzle exit diameter. The amplitude of wall pressure fluctuations subsides as the distance increases, but the maximum mean pressure level at the plate is achieved when the distance is about 4D high. The frequency of the wall pressure is estimated at 6.0 kHz, 9.3 kHz, and 10.0 kHz as the impinging distance varies from 3D, 4D, to 6D, respectively.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1595-1600
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• 2004

When a shock wave arrives at a duct, an impulsive wave is discharged from the duct exit and causes serious noise and vibration problems. In the current study, the characteristics of the impulsive wave discharged from a partial closed duct exit is numerically investigated using a CFD method. The Yee-Roe- Davis's total variation diminishing(TVD) scheme is used to solve the axisymmetric, unsteady, compressible Euler equations. With several partial closed duct exits, the Mach number of the incident shock wave $M_s$ and the distance L/D between the duct exit and a flat plate are varied in the range of $M_s$ = 1.01 ${\sim}$ 1.50 and L/D = 1.0 ${\sim}$ 4.0, respectively. The results obtained show that the magnitude of the impulsive wave impinging upon the flat plate strongly depends upon $M_s$, L/D and the partial closure of duct exit. The impulsive wave on the flat plate can be considerably alleviated by the partial closure of duct exit and, thus, the present method can be a passive control for the impulsive wave.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.195-195
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• 2000

TFT-LCD의 제조공정은 박막층의 식각 공정에 대해 기존의 습식 공정을 대치하는 건식식각이 선호되고 있다. 건식 식각 공정은 반도체 공저에 응용되면서 소자의 최소 선폰(CD)이 감소함에 따라 유도결합셩 프라즈마를 비롯한 고밀도 플라즈마 이용한 플라즈마 장비 사용이 증가하는 추세이다. 여기에 평판디스플레이의 공정을 위해서는 대면적과 사각형 기판에 대한 균일도를 보장할 수 있는 고밀도의 균일한 플라즈마 유지가 중요하다. 본 실험에서는 자장강화된 유도결합형 플라즈마의 플라즈마 밀도 및 균일도를 살펴보고 TFT-LCD에 gate 전극으로 사용되는 Al-Nd 박막의 식각을 통하여 식각균일도와 식각속도 및 식각 선택도 등의 건식 식각 특성을 보고자 한다. 영구자석 및 전자석의 설치는 사각형의 유도결합형 플라즈마는 소형 영구자석을 배열하여 부착하였으며, 외부에는 chamber와 같이 사각형태의 전자석을 500mm$\times$500mm의 크기를 갖는 z축 방향의 Helmholtz형으로 제작하였다. 더. 영구자석 배열에 대해서는 자석간의 거리와 세기 변화를 조합하여 magnetic cusping의 변화를 주었으며 전자석의 세기는 전류값을 기준으로 변화시켜 보았다. 실험을 통하여 플라즈마 균일도를 5% 이하로 개선하고 이러한 균일도를 유지하며 플라즈마 밀도를 높일 수 있는 조건을 찾을 수 있었다. 이러한 적합화된 조건에서 저장강화된 유도결합형 프라즈마를 Al-Nd 박막 식각에 응용한 결과, Al-Nd의 식각속도 및 식각 선택도는 유도결합형 프라즈마에 비해 크게 증가하였으며, 식각균일도가 개선되는 것을 관찰하였다. 또한 electrostatic probe(Hiden, Analytical)를 이용하여 Al-Nd 식각에 사용된 반응성 식각가스에 대한 저장강화된 유도결합형 플라즈마의 특성 분석을 수행하였다.c recoil detection, Rutherford backscattering spectroscopy, X-ray diffraction, secondary electron microscopy, atomic force microscoy, $\alpha$-step, Raman scattering spectroscopu, Fourier transform infrared spectroscopy 및 micro hardness tester를 이용하여 기판 bias 전압이 DLC 박막의 특성에 미치는 영향을 조사하였다. 분석결과 본 연구에서 제작된 DLC 박막은 탄소와 수소만으로 구성되어 있으며, 비정질 상태임을 알 수 있었다. 기판 bias 전압의 증가에 따라 박막의 두께가 감소됨을 알 수 있었고, -150V에서는 박막이 거의 만들어지지 않았으며, -200V에서는 기판 표면이 식각되었다. 이것은 기판 bias 전압과 ECR 플라즈마에 의한 이온충돌 효과 때문으로 판단되며, 150V 이하에서는 증착되는 양보다 re-sputtering 되는 양이 더 많을 것으로 생각된다. 기판 bias 전압을 증가시킬수록 플라즈마에 의한 이온충돌 현상이 두드러져 탄소와 결합하고 있던 수소원자들이 떨어져 나가는 탈수소화 (dehydrogenation) 현상을 확인할 수 있었으며, 이것은 C-H 결합에너지가 C-C 결합이나 C=C 결합보다 약하여 수소 원자가 비교적 해리가 잘되므로 이러한 현상이 일어난다고 판단된다. 결합이 끊어진 탄소 원자들은 다른 탄소원자들과 결합하여 3차원적 cross-link를 형성시켜 나가면서 내부 압축응력을 증가시키는 것으로 알려져 있으며, hardness 시험 결과로 이것을 확인할 수 있었다. 그리고 표면거칠기는 기판 bias 전압을 증가시킬수록 더 smooth 해짐을 확인하였다.인하였다.을 알 수 있