• 한국결정성장학회지
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• 제15권1호
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• pp.21-26
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• 2005

세라믹 분말 가압 성형 공정을 전산모사 하고 패킹의 임의성과 입자 배열의 효과를 평가하기 위해서 유사한 임의 다중 입자 배열을 사용하여 2차원 막대 배열 가압 성형 모델을 도입하였다. 3개의 Al₂O₃ 입자와 3개의 Al 입자를 가지고 기공과 관련된 가압 성형 공정을 균질화 탄성계수를 사용하여 외연적 유한요소 해석하였다. 해석 결과는 이전 해석 결과 및 실험 결과와 비교하였다. 마지막으로, 분말 입자의 마찰계수와 상대밀도의 관계를 얻기 위한 해석이 수행되었다.

• 태양에너지
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• 제15권1호
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• pp.85-94
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• 1995

본 연구는 2차원 충돌분류계의 포텐셜코어영역(H/B=2)내에서 전열증진을 목적으로 전열면 앞에 폭 6mm인 정 4각 rod군을 설치하고 rod와 전열면간의 간극(C=1, 2, 4, 6mm)과 rod와 rod사이의 피치(P=30, 40, 50mm)를 변화시킬때의 유동특성과 전열특성을 실험적으로 규명하고 rod를 설치하지 않았을 경우와 비교 검토한 것으로 간극변화시에는 C=1mm인 경우가 전열성능이 가장 우수하였으며, rod의 피치(P)를 변화시킨 경우에는 rod가 없는 평판에 비해 각각 약 1.6배의 평균전열증진율이 나타났다.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1659-1666
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• 2001

The objective of this study was to investigate the characteristics of air flow and heat transfer caused by trapezoid rods array in impinging air jet system. Trapezoid rods have been set up on front of flat plate to act as a turbulence promoter. Local Nusselt numbers were determined as a function of three parameters : (a) the space from re(Is to heating surface(C=1, 2, 4mm), (b) the pitch between each rods(P=30, 40, 50mm), (c) the distance from nozzle exit to flat plate(H/B=2, 6, 10). The measurements were compared with those of the experiment without trapezoid rods. As a result, when rods are installed in front of the impinging palate, the acceleration of the flow and the eddies due to the rods seem to contribute to the heat transfer enhancement. Heat transfer performance was best under the condition of C=1mm and as the pitch is 30mm. The maximum rate of heat transfer augmentation is about 1.9 times greater compared to that without trapezoid rods.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.379-381
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• 2011

Direct numerical simulations (DNSs) of spatially developing turbulent boundary layers (TBLs) over two-dimensional (2-D) and rod and three-dimensional (3-D) cube rough walls were performed to investigate the effects of streamwise spacing on the properties of the TBL The 2-D and 3-D roughness were periodically arranged in the downstream direction with pitches of px/k=2, 3, 4, 6, 8 and 10 and for the cube, the spanwise spacing is fixed to pz/k=2 with staggered array, where px and pz are the streamwise and spanwise spacings of the roughness and k is the roughness height. Inspection of the Reynolds stresses showed that except for px/k=2 and 3 over the 2-D rough walls, the effects of the surface roughness extend to the outer layer over the 2-D and 3-D rough walls and the magnitude of the Reynolds shear stress in the outer layer is increased with proportion to px/k. However, such results are contrary to the trends of form drag, roughness junction and roughness length against px/k, which showed the maximum values at px/k=8 and 4 over the 2-D and 3-D rough walls respectively.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.476-479
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• 2005

In this study, the process parameters in powder compaction are optimized for getting high relative densities. To find optimized parameters, the analytic models of powder compaction are firstly prepared by 2-dimensional rod arrays with random green densities using a quasi-random multi-particle array. Then, using finite element method, the changes in relative densities are analyzed by varying the size of the particle, the amplitude of cyclic compaction, and the coefficient of friction, which influence the relative density in cyclic compactions. After the analytic function of relative density associated process parameters are formulated by aid of the response surface method, the optimal conditions in powder compaction process are found by the grid search method.

• 한국재료학회지
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• 제21권12호
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• pp.697-702
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• 2011

Two-dimensional (2D) nano patterns including a two-dimensional Bravais lattice were fabricated by laser interference lithography using a two step exposure process. After the first exposure, the substrate itself was rotated by a certain angle, $90^{\circ}$ for a square or rectangular lattice, $75^{\circ}$ for an oblique lattice, and $60^{\circ}$ for a hexagonal lattice, and the $90^{\circ}$ and laser incident angle changed for rectangular and the $45^{\circ}$ and laser incident angle changed for a centered rectangular; we then carried out a second exposure process to form 2D bravais lattices. The band structure of five different 2D nano patterns was simulated by a beam propagation program. The presence of the band-gap effect was shown in an oblique and hexagonal structure. The oblique latticed ZnO nano-photonic crystal array had a pseudo-bandgap at a frequency of 0.337-0.375, 0.575-0.596 and 0.858-0.870. The hexagonal latticed ZnO nano-crystallite array had a pseudo-bandgap at a frequency of 0.335-0.384 and 0.585-0.645. The ZnO nano structure with an oblique and hexagonal structure was grown through the patterned opening window area by a hydrothermal method. The morphology of 2D nano patterns and ZnO nano structures were investigated by atomic force microscopy and scanning electron microscopy. The diameter of the opening window was approximately 250 nm. The height and width of ZnO nano-photonic crystals were 380 nm and 250 nm, respectively.

• 한국결정성장학회지
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• 제15권1호
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• pp.27-33
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• 2005

본 연구에서는 세라믹 제품의 고밀도를 얻기 위해 분말 압축 성형 공정 변수의 최적화가 수행되었다. 이를 위해 먼저 임의의 초기 밀도를 갖는 분말 성형체를 모델링하였다. 그리고 반복 가압 성형 공정시 상대밀도에 영향을 주는 Al₂O₃ 입자의 크기, 반복 가압 진폭 크기, 그리고 마찰계수에 따른 상대밀도의 변화를 유한요소법으로 해석하였다. 유한요소 해석 결과를 반응 표면법으로 수식화한 후, 격자 탐색법으로 가압 성형 공정 변수의 최적 조건을 찾았다. 입자의 크기가 22.5 ㎛, 반복 가압 진폭이 75 MPa, 마찰계수가 0.1103인 경우에 상대 밀도 값이 0.9390으로 최대가 되었다.