• 제목/요약/키워드: non-uniform flow

검색결과 329건 처리시간 0.047초

균일한 에피층 성장을 위한 입구 유속분포 최적화 (Optimization of inlet velocity profile for uniform epitaxial growth)

  • 조원국;최도형;김문언
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 1998년도 추계 학술대회논문집
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    • pp.121-126
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    • 1998
  • A numerical optimization procedure is developed to find the inlet velocity profile that yields the most uniform epitaxial layer in a vertical MOCVD reactor. It involves the solution of fully elliptic equations of motion, temperature, and concentration; the finite volume method based on SIMPLE algorithm has been adopted to solve the Navier-Stokes equations. The overall optimization process is highly nonlinear and has been efficiently treated by the sequential linear programming technique that breaks the non-linear problem into a series of linear ones. The optimal profile approximated by a 6th-degree Chebyshev polynomial is very successful in reducing the spatial non-uniformity of the growth rate. The optimization is particularly effective to the high Reynolds number flow. It is also found that a properly constructed inlet velocity profile can suppress the buoyancy driven secondary flow and improve the growth-rate uniformity.

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불균일 벽면 온도를 갖는 Rayleigh-Benard 문제에서의 유동의 다수성 (Multiplicity of Flows in a Rayleigh-Benard Problem with Non-Uniform Wall Temperatures)

  • 유주식;김용진
    • 대한공업교육학회지
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    • 제30권2호
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    • pp.123-129
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    • 2005
  • A Rayleigh-Benard problem with non-uniform wall temperatures of the form, $T_L=T_1+{\delta}{\Delta}T{\sin}kx$ and $T_U=T_2-{\delta}{\Delta}{\sin (kx)$, is numerically investigated. In the conduction-dominated regime with small a Rayleigh number, a two-tier structure appears with two counter-rotating rolls stacked on the top of each other. The flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The multicellular flows at high Rayleigh numbers consist of approximetely square-shape cells. Four multiple flows and dual flows classified by the number of cells are found at k=0.5 and k=1, respectively.

스핀들 모드하의 전기수력학적 미립화를 통한 균일 미세액적 생성 (Generation of uniform Fine Droplets Under Spindle Mode in Electrohydrodynamic Atomization)

  • 이상용;김명찬;김상수;김유동
    • 대한기계학회논문집B
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    • 제25권7호
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    • pp.923-932
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    • 2001
  • A series of experiments were conducted to generate fine liquid(water) drops through the electrohydrodynamic atomization process. The atomization mode depended on flow rate and DC voltage input. For water, having electric conductivity larger than 10(sup)-7S/m, the spindle mode turned out to be the only mode to generate uniform-size drops within the range of 30-450 microns that have wide applications. Within this mode, both the uniformity and the fineness of drops were improved at an optimum voltage input for a given flow rate. This optimum voltage increased with increasing of the liquid flow rate. Another important parameter considered was the nozzle material with different electric conductivity and liquid wettability. A stainless-steel nozzle (the material with high electric conductivity and high liquid wettability) and a silica nozzle (the electrically non-conducting material with low liquid wettability) were tested and compared; and more uniform drops could be obtained with the silica nozzle.

CCHE1D 모형을 이용한 저수지 붕괴에 따른 하상변동 해석 (Numerical Analysis of River Bed Change Due to Reservoir Failure Using CCHE1D Model)

  • 손인호;김병현;손아롱;한건연
    • 대한토목학회논문집
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    • 제36권2호
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    • pp.219-229
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    • 2016
  • 본 연구에서는 저수지의 붕괴로 인한 하류부 하천의 하상변동에 대한 해석을 수행하였다. 저수지 붕괴에 따른 1차원 비평형, 비균일 유사의 이송과 하상 변동을 연구를 위해 CCHE1D 모형을 이용하였다. CCHE1D 모형은 비평형 및 비균일 유사해석을 위해 조정거리와 분류된 입자의 입경을 사용하며, 하상 물질의 교환을 위한 혼합층의 개념이 사용된다. CCHE1D 모형을 1996년 저수지 붕괴가 발생한 Ha!Ha!강 유역에 적용하여 저수지 붕괴로 인한 하류부의 비평형, 비균일 유사이송을 해석하고, 계산 결과를 저수지 붕괴전 후에 하류부 실측 하상과 비교하였다. 또한, 조정계수($L_{s,b}$), 비평형 계수(${\alpha}_s$), 혼합층 두께(${\delta}_m$), 공극률(p')을 포함하는 주요 매개변수에 대한 민감도를 분석하였으며, 대상유역에서는 비평형 계수가 하상변동에 가장 큰 영향을 주는 것으로 나타났다.

충격압출 공정을 이용한 직사각형 배터리 케이스 성형 시 불균일 금속 유동 발생 원인 고찰 (An investigation of non-uniform metal flow during rectangular battery case using impact extrusion process)

  • 임재혁;김용배;이종섭
    • Design & Manufacturing
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    • 제10권2호
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    • pp.24-28
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    • 2016
  • In this study, relevant to impact extrusion process of the rectangular batter case for electric vehicles, numerical and experimental analyses were conducted to reduce the earring defects induced in the unevenness of metal flow. Since the earring is caused by the non-uniform metal flow induced in the friction and aspect ratio in the bottom section. As a way to reduce the earring, variable land die concept was applied. In order to analyze numerically the complex metal flow by using commercial finite element package, DEFORM 3D, impact extrusion process was simplified in upsetting mode at bottom section and extrusion mode at land section. The impact extrusion experiments were conducted to verify the assessment of process parameter for impact extrusion. As results, variable land die which has longer longitudinal section makes reduce earring defects. In addition, it was confirmed that the effect that slug shape like dog-bone also can reduce the earring. This study is expected to be able to present the useful design guidelines for manufacturing the battery case.

비축대칭 평금형 압출에서 유동제어에 관한 실험적 연구-II (Experimental investigation on the flow control in non-axisym- metric flat die extrusion-II)

  • 김영호;배원병;강범수;박재우
    • 한국정밀공학회지
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    • 제14권3호
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    • pp.130-136
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    • 1997
  • The velocity distrubution at the exit of extrusion die depends on the width of bearing land very much. When uniform bearing land without flow guide is used, the material which is extended through the same die does not, deflect to the constant direction, but when the flow guide is equipped and then the volume compensation is done accurately, the material deflects to one constant direction. Therfore, the part of problem can be known exactly, and extrusion products of straight shape can be produced by the corrected bearing land width.

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이동식 플랫폼에서 발사되는 비행체의 날개 전개 공력 하중에 관한 연구 (A Study on Aerodynamic Loads of a Deploying Wing Launched from a Mobile Platform)

  • 이영환
    • 한국군사과학기술학회지
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    • 제22권3호
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    • pp.353-359
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    • 2019
  • In this study, a aerodynamic loads prediction to design a deploying device of folded fin was introduced. In general, resultant flow conditions around the fin are used to obtain deploying moments and required energy. However, when it comes to the air vehicles launched from a mobile platform, more specific flow conditions can be provided. With the conditions, the design criteria can be calculated more realistically. In this study, therefore, aerodynamic moments induced by aerodynamic loads and energy required in deployment were calculated using wind-over-deck(WOD) velocity, combination of a platform velocity and a wind velocity. For the calculation, wind tunnel test was conducted on various angle of attack, side slip angles, and folding angles. It was found that the aerodynamic moments and the energy required in deployment using the non-uniform flow due to the velocity components were less than those using the uniform flow without the components.

구조물의 비접촉 비파괴 검사를 위한 레이저 초음파법 적용 (Laser-Ultrasonics Application for Non-Contact and Non-destructive Evaluation of Structure)

  • 김재열;송경석;양동조
    • 한국공작기계학회논문집
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    • 제14권4호
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    • pp.49-54
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    • 2005
  • Measuring defects on the inside and on the surface of a steel structure is very important technology in order to predict the life span of the structure. In particular, a place with a high probability that it may contain defects is a welded part and it is very important to check defects in the part, absence/presence of non-uniform substances, its shape, and the location. Many non-destructive tests can be applied, but the ultrasonic flow detection test is widely used with some advantages. The ultrasonic flow detection test, however, cannot be applied when there is a problem by a contact medium between PZT and a specimen, in case of a small and complicated shape or a moving object or when the specimen is hot. In this study, to solve the problems of the contact ultrasonic flow detection test, the non-contact ultrasonic flow detection test for sending/receiving ultrasonic waves using lasers was described. I intended to develop a non-destructive detection system applying the laser application ultrasonic test to a steel structure by detecting the defects inside of and on the surface of the specimen.

균일 층류유동중에 있는 원형 실린더 주위의 열영동에 의한 입자 부착 (Thermophoretic Particle Deposition Around a Circular Cylinder in a Uniform Laminar Air Dlow)

  • 홍기혁;강신형
    • 대한기계학회논문집B
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    • 제20권2호
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    • pp.641-648
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    • 1996
  • Thermophoretic particle deposition on a circular cylinder in a uniform laminar air flow was numerically investigated using a control volume method based on the generalized non-orthogonal coordinate system. Variation of air properties due to the change of temperature was taken into account. Effects of variable property on the distribution of heat transfer and deposition rates of particle were discussed. A new correlation of thermophoretic particle deposition on a circular cylinder was proposed in the present study.