• 한국전산구조공학회논문집
• /
• 제27권3호
• /
• pp.183-189
• /
• 2014

본 연구에서는 다면체 요소의 개발을 위하여 Wachspress 좌표계와 이동최소자승 근사를 기반으로하는 형상함수와 수치적분 방법을 제시하고 있다. 사면체 요소를 사면체 영역으로 분할하여 형상함수가 구성이 되고 이 영역을 사용한 일관성있는 수치적분이 수행되게 된다. 다면체 요소 면에서 Wachspress 좌표계를 사용하고 요소 내부에서 라플라스 방정식을 적용하여 이동최소자승 근사의 가중함수를 정의하게 된다. 본 연구에서 개발되는 다면체 요소의 형상함수와 수치적분 방법은 일반적인 유한요소와 유사한 특성을 갖게 되는데 수치 예제를 통하여 유효성을 보여주었다.

• 한국정밀공학회지
• /
• 제22권4호
• /
• pp.194-202
• /
• 2005

The objective of this paper is to develop a multi-functional hotwire cutting system (MHC) using EPS-foam block or plate as the working material. Because the MHC apparatus employs a four-axis synchronized hotwire cutter with the structure of two XY movable heads and a turntable, it allows the easy fabrication of various 3D shapes, such as (1) an axisymmetric shape or a sweeping cross-sectioned pillar shape using the hot-strip in the form of sweeping surface and EPS foam block on the turntable, (2) a polyhedral complex shape using the hotwire and EPS foam block on the turntable, and (3) a ruled surface approximated freeform shape using the hotwire and EPS foam plate. In order to examine the applicability of the developed MHC apparatus, an axisymmetric shape, a polyhedral shape and a large-sized freeform shape were fabricated on the apparatus.

• 한국세라믹학회지
• /
• 제43권11호
• /
• pp.728-733
• /
• 2006

The equilibrium or growth shape of ceramic materials is classified largely into two categories according to the thermodynamic conditions imposed. One is a polyhedral shape where the surface free energy is anisotropic, and the other a spherical shape where the surface free energy is isotropic. In the case of grains with a polyhedral shape of anisotropic surface free energy, socalled abnormal grain growth usually takes place due to a significant energy barrier for a growth unit to be attached to the crystal surface. In the case of grains with a spherical shape of isotropic surface free energy, however, normal grain growth with a uniform size distribution takes place. In this contribution, the state-of-the-art of our current understanding of the relationship between the crystal shape and the microstructure evolution during the sintering of ceramic materials in the presence of a liquid phase was discussed.

• 한국정밀공학회지
• /
• 제10권4호
• /
• pp.81-93
• /
• 1993

The three dimensional(3D) shape reconstruction from two dimensional(2D) cross-sections can be completed through three main phases : the input compilation, the triangular grid formation, and the smooth surface construction. In the input compilation phase, the cross-sections are analyzed to exctract the input data required for the shape reconstruction. This data includes the number of polygonized contours per cross-section and the vertices defining each polygonized contour. In the triangular grid formation phase, a triangular grid, leading to a polyhedral approximations, is constructed by extracting all the information concerning contour links between two adjacent cross- sections and then performing the appropriate triangulation procedure for each contour link. In the smooth surface construction phase, a smooth composite surface interpolating all vertices on the triangular grid is constructed. Both the smooth surface and the polyhedral approximation can be used as reconstructed models of the object. This paper proposes a new method for reconstructing the geometric model of a 3D objdect from a sequence of planar contours representing 2D cross-sections of the objdect. The method includes the triangular grid formation algorithms for contour closing, one-to-one branching, and one-to-many braanching, and many-to-many branching. The shape reconstruction method has been implemented on a SUN workstation in C.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2013년도 춘계학술대회 논문집
• /
• pp.919-920
• /
• 2013

• Corrosion Science and Technology
• /
• 제13권4호
• /
• pp.145-151
• /
• 2014

The objectives of this study are to investigate the effect of the concentration ratios of Ni and Fe ions on crud deposition onto the fuel cladding surface in the simulated primary environments of a pressurized water reactor. Crud deposition tests were conducted in the Ni and Fe concentration ratios of 20:20 ppm, 39:1 ppm and 1:39 ppm at $325^{\circ}C$ for 14 days. In the case of the same Ni and Fe ion ratio (20:20), nickel ferrite with a polyhedral shape was formed. Nickel oxide deposits with a needle shape were formed in the condition of high Ni to Fe ion ratio (39:1), While polyhedral iron oxide and needle-like nickel oxide formed in the condition of low Ni to Fe ion ratio (1:39). The amount of deposits increased, when Fe oxides were formed. This indicates that Fe rich oxides stimulated Ni oxide deposition.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2004년도 추계학술대회 논문집
• /
• pp.1414-1417
• /
• 2004

A thick-layered RP process, transfer-type variable lamination manufacturing using expandable polystyrene foam (VLMST) has been developed to have the advantageous characteristics such as high building speed, low cost for introduction and maintenance of VLM-ST apparatus, and little staircase surface irregularities of parts. However, VLM-ST has difficulty fabricating an axisymmetric shape and a large-sized freeform shape because of the limited sloping angles and small build size. The objective of this paper is to develop a multi-functional hotwire cutting system using EPS-foam (MHC). MHC employs a four-axis synchronized hotwire cutter with the structure of two XY movable heads and a turntable. In order to examine the applicability of the developed MHC apparatus, an axisymmetric shape, a polyhedral shape and a large-sized freeform shape were fabricated on the apparatus.

• 폴리머
• /
• 제31권6호
• /
• pp.461-468
• /
• 2007

폴리에스터와 trisilanolisobutyl polyhedral oligomeric silsesquioxane(TBPOSS)으로 제조된 나노복합재료에 존재하는 응집체의 구조를 이해하기 위하여 SEM-EDS 분석과 1,1,1,3,3,3-hexafluoro-2-propanol(HFIP) 용매에 녹인 뒤 레이저 광산란법이 실시되었다. SEM에서 평균 직경 120 nm로 나타난 구형 응집체는 가교화된 마이크로겔이 아니라, 320개의 TBPOSS 분자들과 폴리에스터 분절들이 교대로 연결된 선형 중합체 사슬(무게평균 분자량=$2.3{\times}10^6\;g/mol$)이며, 이들은 매트릭스의 폴리에스터와의 화학조성 차이 때문에 상분리된 것으로 여겨진다. 반면에 무게평균 분자량이 $4.0{\times}10^4\;g/mol$인 매트릭스의 폴리에스터는 분자당 2.5개의 TBPOSS 분자를 포함하고 있는 것으로 나타났다. 또한 넣어준 TBPOSS의 약 93%가 매트릭스에 존재하며 나머지 7%는 구형 응집체에 분포하고 있다는 것도 밝혀졌다.

• 한국전산유체공학회지
• /
• 제11권1호
• /
• pp.8-15
• /
• 2006

The existing approximations of diffusion flux in unstructured cell-centered finite volume methods are examined in detail with each other and clarified to have indefinite expressions in several respects. A new numerical approximation of diffusion flux at cell face center is then proposed, which is second-order accurate even on irregular grids and may be easily implemented in CFD code using cell-centered finite volume method with unstructured grids composed of arbitrary convex polyhedral shape.

• 한국결정학회지
• /
• 제3권1호
• /
• pp.1-8
• /
• 1992

졸겔 및 공침법으로 제조된 티탄산 납 분말의 형태를 하소온도와 하소시간의 함수로 조사하였다. 질산 납과 사염화 티탄의 혼합용액을 사용하여 40-43℃ 및 9.0-9.7 pH에서 PbTiO3 전구체를 제조하였으며, 350-1000℃에서 1-10시간동안 공기중에서 이들을 히소시켰다. 하소온도와 시간의 증가에 따라 입자의 크기가 증가하고 응집이 심화되었다. 졸겔법으로 제조된 분말을 700℃에서 히소시킬 때, 초기에 형성된 침상형 혹은 각주 형의 입자들은 하소가 진행됨에 따라 다면체형으로 변한뒤, 모서리가 둥근 다면체형 입자로 성장하였다. 공침법으로 제조된 분말은 결정화 과정중에 형태가 변화되지 않았다.