• Title/Summary/Keyword: high-aspect-ratio

검색결과 949건 처리시간 0.03초

고전계 전기산화에 의한 나노다공성 알루미나 멤브레인의 제조 (Fabrication of Nanoporous Alumina Membrane by High- Field Anodization)

  • 김민우;현상철;하윤철
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2010년도 춘계학술대회 논문집
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    • pp.45-45
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    • 2010
  • Nanoporous anodic alumina membranes (NAAM) with high aspect ratio, self-ordered pore array were fabricated by high-field 2-step anodization method. High voltages of 80, 100, 120 and 140 V as well as 40 V for comparison were applied to an aluminum anode with respect to a Pt cathode immersed both in 0.3M oxalic acid solution in order to investigate the self-ordering characteristics of the nanoporous structure. The pore structures, including interpore distance, pore size, pore density, and porosity as well as the ordering characteristic were analyzed using field-enhanced scanning electron microscopy (FE-SEM) and the corresponding Fourier-transformed images. The nanoporous structure could be produced for all the voltage conditions, but the well-ordered through-hole pore without a branched structure seemed to occur only at 40 and 140 V. It turned out that the growth rate under 140 V high-field anodization was about 40 times higher than under conventional 40 V mild anodization, which enabled the fast fabrication of self-ordered, high aspect ratio NAAMs.

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Vortex-induced vibration characteristics of a low-mass-ratio flexible cylinder

  • Quen, Lee Kee;Abu, Aminudin;Kato, Naomi;Muhamad, Pauziah;Siang, Kang Hooi;Hee, Lim Meng;Rahman, Mohd Asamudin A
    • Structural Engineering and Mechanics
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    • 제75권5호
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    • pp.621-631
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    • 2020
  • A laboratory experiment is conducted is to investigate the behaviour of a low-mass-ratio and high aspect ratio flexible cylinder under vortex-induced vibration (VIV). A flexible cylinder with aspect ratio of 100 and mass ratio of 1.17 is towed horizontally to generate uniform flow profile. The range of Reynolds number is from 1380 to 13800. Vibration amplitude, in-line and cross-flow frequency response, amplitude trajectory, mean tension variation and hydrodynamic force coefficients are analyzed based on the measurement from strain gauges, load cell and CCD camera. Experimental results indicate that broad-banded lock-in region is found for the cylinder with a small Strouhal number. The frequency switches in the present study indicates the change of the VIV phenomenon. The hydrodynamic force responses provide more understanding on the VIV of a low mass ratio cylinder.

등온 경계 조건을 가지는 마이크로채널 히트 싱크의 열성능 해석을 위한 평균 접근법 (Averaging Approach for Microchannel Heat Sinks Subjected to the Uniform Wall Temperature Condition)

  • 김동권;김성진
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 추계학술대회
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    • pp.1247-1252
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    • 2004
  • The present paper is devoted to the modeling method based on an averaging approach for thermal analysis of microchannel heat sinks subjected to the uniform wall temperature condition. Solutions for velocity and temperature distributions are presented using the averaging approach. When the aspect ratio of the microchannel is higher than 1, these solutions accurately evaluate thermal resistances of heat sinks. Asymptotic solutions for velocity and temperature distributions at the high-aspect-ratio limit are alsopresented by using the scale analysis. Asymptotic solutions are simple, but shown to predict thermal resistances accurately when the aspect ratio is higher than 10. The effects of the aspect ratio and the porosity on the friction factor and the Nusselt number are presented. Characteristics of the thermal resistance of microchannel heat sinks are also discussed.

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기둥 형상비에 따른 플랫 플레이트 기둥-슬래브 접합부의 거동특성 (Seismic Behavior of Column-Slab Connections with Different Column Aspect Ratio)

  • 천영수;이현호;이도범;김진수;허무원
    • 한국콘크리트학회:학술대회논문집
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    • 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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    • pp.30-33
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    • 2006
  • The purpose of this research is to study the seismic behavior of interior column-slab connections with different column aspect ratio, when subjected to combined gravity and cyclic lateral loading. The control specimen had square column, while the other specimens had rectangular column with aspect ratio of 0.5 and 2.0. From the test results, all of the specimens sustain lateral drifts as high as 4% with no more than a 20% decrease in peak lateral load capacity. And it appears that KBC Code(2005) procedure may be unconservative for connections with different column aspect ratio.

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단결정 다이아몬드 공구를 이용한 미세 패턴 가공성에 대한 실험적 분석 (Experimental Investigation on Machining Feasibility of Micro Patterns using a Single Crystal Diamond Tool)

  • 김현철
    • 한국기계가공학회지
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    • 제11권5호
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    • pp.76-81
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    • 2012
  • The continuing demand for increasingly slimmer and brighter liquid crystal display(LCD) panels has led to an increased focus on the role of the light guide panels(LGPs) or optical films that are used to obtain diffuse, uniform light from the backlight unit(BLU). And the most basic process in the production of such BLU components is the micromachining. LCD BLUs comprise various optical elements such as a LGP, diffuser sheet, prism sheet, and protector sheet with micro patterns. High aspect ratio patterns are required to reduce the number of sheets and enhance light efficiency, but there is a limit to the aspect ratio achievable for a given material and cutting tool. Therefore, this study comprised a series of experimental evaluations conducted to determine the machining feasibility in microcutting various aspect ratio patterns on electroless nickel plated die materials when using single-crystal diamond tools. Cutting performance was evaluated at various cutting speeds and depths of cut using different machining methods and machine tools.

예조건화된 압축성유동 수치기법에서의 풍상차분법의 수치특성 검토 (Numerical Characteristics of Upwind Schemes for Preconditioned Compressible Navier-Stokes Equations)

  • 길재흥;이두환;최윤호;권장혁;이승수
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2002년도 추계 학술대회논문집
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    • pp.95-102
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    • 2002
  • Studies of the numerical characteristics of implicit upwind schemes, such as upwind ADI, Line Gauss-Seidel(LGS) and Point Gauss-Seidel(LU) algorithms, for preconditioned Navier-Stokes equations ate performed. All the algorithms are expressed in approximate factorization form and Von Neumann stability analysis and convergence studies are made. Preconditioning is applied for efficient convergence at low Mach numbers and low Reynolds numbers. For high aspect ratio computations, the ADI and LGS algorithms show efficient and uniform convergence up to moderate aspect ratio if we adopt viscous preconditioning based on min- CFL/max- VNN time-step definition. The LU algorithm, on the other hand, shows serious deterioration in convergence rate as the grid aspect ratio increases. Computations for practical applications also verify these results.

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평균 접근법을 이용한 전자 장치 냉각용 마이크로 채널 히트 싱크에 대한 연구 (Study on the Averaging Approach for Microchannel Heat Sinks for Electronics Cooling)

  • 김동권;김성진
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 춘계학술대회
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    • pp.1430-1435
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    • 2004
  • The present paper is devoted to the modeling based on an averaging approach for microchannel heat sinks. Firstly, analytic solutions for velocity and temperature distributions for low-aspect-ratio microchannel heat sinks are presented by using the averaging approach. When the aspect ratio of the microchannel is smaller than 1, analytic solutions accurately evaluate thermal resistances of heat sinks while the previous model cannot predict thermal resistances. Secondly, asymptotic solutions for velocity and temperature distributions at low-aspect-ratio limit and at high-aspect-ratio limit are presented by using the scale analysis. Asymptotic solutions are very simple, but shown to predict thermal resistances accurately.

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강재의 피로균열전파율에 미치는 시험편 크기의 영향 (Effect of Specimen Size on Fatigue crack Growth Rate in Steels)

  • 안석화
    • 한국해양공학회지
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    • 제14권2호
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    • pp.99-105
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    • 2000
  • This paper describes the effect of specimen size on fatigue crack growth rate for the offshore structural high-tensile-strength steel BS4360 and machine structural steel SM45C. The purpose of the present study is to investigate the effect of stress ratio aspect ratio specimen width and specimen thickness of the fatigue crack growth behavior. Compact tension specimens with a LT orientation for BS4360 and SM45C steels were used, All testing was done at constant stress intensity factor range controlled fatigue crack growth condition. The investigation demonstrates that the fatigue crack growth rate is increased with increasing stress ratio and specimen thickness and is decreased with increasing specimen width. The fatigue crack growth rate is unaffected by aspect ratio until a/W=0.50 but is increased by increasing spect ratio from a/W=0.55.

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스탬퍼 가열/냉각을 이용한 고세장비 나노 구조물 성형 (Injection Molding of High Aspect Ratio Nano Features Using Stamper Heating/Cooling Process)

  • 유영은;최성주;김선경;최두선;황경현
    • 소성∙가공
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    • 제16권1호
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    • pp.20-24
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    • 2007
  • Polypropylene substrate with hair-like nano features(aspect $ratio{\sim}10$) on the surface is fabricated by injection molding process. Pure aluminum plate is anodized to have nano pore array on the surface and used as a stamper for molding nano features, The size and the thickness of the stamper is $30mm{\times}30mm$ and 1mm. The fabricated pore is about 120nm in diameter and 1.5 um deep. For molding of a substrate with nano-hair type of surface features, the stamper is heated up over $150^{\circ}C$ before the filling stage and cooled down below $70^{\circ}C$ after filling to release the molded part. For heating the stamper, stamper itself is used as a heating element by applying electrical power directly to each end of the stamper. The stamper becomes cooled down without circulation of coolant such as water or oil. With this new stamper heating method, nano hairs with aspect ratio of about 10 was successfully injection molded. We also found the heating & cooling process of the stamper is good for releasing of molded nano-hairs.