• 대한기계학회논문집
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• 제18권12호
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• pp.3159-3174
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• 1994

A simple octree encoding algorithm based on a tetrahedron root has been developed to be used for fully automatic generation of three dimensional finite element meshes. This algorithm starts octree decomposition from a tetrahedron root node instead of a hexahedron root node so that the terminal mode has the same topology as the final tetrahedral mesh. As a result, the terminal octant can be used as a tetrahedral finite element without transforming its topology. In this part(I) of the thesis, an efficient algorithm for the tetrahedron-based octree is proposed. For this development, the following problems have been solved, : (1) an efficient data structure for storing the octree and finite elements, (2) an encoding scheme of a tetrahedral octree, (3) a neighbor finding technique for the tetrahedron-based octree.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.700-705
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• 2004

Shell finite elements are widely used for the analysis of thin section objects such as sheet metal parts, automobile bodies and et al. due to their computational efficiency. Since many of input data for finite element analysis are given as solid models or triangulated surface models, one should extract midsurface information from these input data initially and then construct shell meshes on the extracted midsurfaces. In this paper, a method of generating shell elements on midsurfaces directly from input models have been proposed. In order to construct shell meshes, the input models should be triangulated on surfaces first, and then tetrahedral elements are generated by using an advancing front method, and finally mid shell surfaces are obtained from tetrahedral meshes. Some examples are given to demonstrate the efficiency of the proposed method.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.209-214
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• 2005

In this paper, finite element simulation of three-dimensional bulk metal forming processes is performed by an automated adaptive tetrahedral mesh generation scheme. A dynamic data exchange scheme is employed between tetrahedral mesh generator and forging simulator to minimize user intervention. Both number of elements and density distributions are controlled by the octree technique. The presented approach is applied to automatic forging simulation in order to evaluate the efficiency of the developed schemes and the simulation results are compared with $DEFORM^{TM}$.

• Bulletin of the Korean Chemical Society
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• 제3권1호
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• pp.5-9
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• 1982

Reactions of cobalt(II) chloride with 2,2'-dipyridylamine (dpa) in alcoholic solutions afford the complex of octahedral $Co(dpa)_2Cl_2{\cdot}CH_3OH$. The octahedral complex is converted to tetrahedral $Co(dpa)Cl_2$ in certain solvents or at the elevated temperature, and the tetrahedral complex is changed to the octahedral one with added dpa. The electronic spectra of the complexes in DMF, measured with various concentrations of 2,2'-dipyridylamine, establish the equilibrium; $td-Co(dpa)Cl_2+dpa_\rightleftarrows^Koh-Co(dpa)_2Cl_2$. The equilibrium constants determined by the analysis of the visible spectra are 6.4, 3.6 and 2.0 $M^{-1}$, respectively, at 25.5, 38.0 and $49.0^{\circ}C,\;with\;{\Delta}H^{\circ}\;and\;{\Delta}S^{\circ}$being -9.5 kcal/mole and -28 eu.

• Bulletin of the Korean Chemical Society
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• 제2권3호
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• pp.79-82
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• 1981

A calculation method of the dipole moments for square planar and tetrahedral complexes by the valence bond method has been developed and an example calculation was carried out choosing the square planar and tetrahedral $[M(Ⅱ)N_2Se_2]$ type complexes. The calculated values of the dipole moments by the valence bond method are higher than those of the approximate orbital method. We found that we may predict the geometric structure of the transition metal complexes comparing the calculated values of the dipole moments with the experimental values. A new method for definition of C' parameter has also developed on the basis of extended Huckel theory.

• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3809-3811
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• 2010

• 한국자기공명학회논문지
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• 제8권2호
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• pp.70-76
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• 2004

ZORA-DFT calculations of $^{11}$B EFG (electric field gradient) tensors for lithium borates, LiB$_3O_5$ (LBO) and Li$_2B_4O_7$ (LTB), were performed. The calculated values of 11B quadrupole coupling constant and asymmetry parameter are in good agreement with the experimental values. The sign of the quadrupole coupling constant for the tetrahedral boron site was deduced from the distortion from the ideal tetrahedral symmetry.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.607-610
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• 2005

A remeshing algorithm using tetrahedral elements has been developed, which is adapted to the mesh density map constructed by a posteriori error estimation. In the finite element analyses of metal forging processes, numerical error increases as deformation proceeds due to severe distortion of elements. In order to reduce the numerical error, the desired mesh sizes in each region of the workpiece are calculated by a posteriori error estimation and the density map is constructed. Piecewise density functions are then constructed with the radial basis function in order to interpolate the discrete data of the density map. The sample mesh is constructed based on the point insertion technique which is adapted to the density function and the mesh size is controlled by moving and deleting nodes to obtain optimal distribution according to the mesh density function and the quality optimization function as well. After finishing the redistribution process of nodes, a tetrahedral mesh is constructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• 정보처리학회논문지A
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• 제10A권1호
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• pp.59-68
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• 2003

3 차원 산포 볼륨 데이터의 모델링(3-D Scattered Data Modeling)은 지질구조 조사, 환경가시화, 초음파 검사 등의 분야에 사용된다. 이러한 분야에 사용되는 데이터는 마칭큐브 알고리즘에서 사용하는 규칙적인 데이터와는 다르게 일반적으로 불규칙적으로 흩어진 데이터이다. 이 논문에서는 우선 불규칙적으로 흩어진 데이터에 적합한 사면체를 영역(domain)으로 하는 볼륨 모델링 기법에 대하여 고찰한다. 다음에 사면체 영역 결정에 애매성이 발생하였을 때 점근선 판정기(asymptotic decider critrion)로 애매성을 해결하는 방법을 제안하고 수식을 구한다. 마지막으로 제안한 방법을 이용하여 간단한 가시화 시스템을 구현하여 구 판정기(sphere criterion)와 비교한다. 사면체의 영역을 결정하는데 있어서 구 판 정기는 점의 좌표만을 이용하나 점근선 판정기는 점의 좌표와 그 점이 가지고 있는 함수 값을 이용하므로 보다 정확한 영역 분할이 가능하다.

• 한국수소및신에너지학회논문집
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• 제27권5호
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• pp.547-553
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• 2016

This paper presents the effect of a grid system on the performance of a small Savonius wind turbine installed side-by-side. Turbine performance is compared using three different grid systems; tetrahedral grid having a concentrated circular grid around turbine rotors, the tetrahedral grid having a concentrated rectangular grid around turbine rotors and the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid. The commercial code, SC/Tetra has been used to solve the three-dimensional unsteady Reynolds-averaged Navier-Stokes analysis in the present study. The Savonius turbine rotor has a rotational diameter of 0.226m and an aspect ratio of 1.0. The distance between neighboring rotor tips keeps the same length of the rotor diameter. The variations of pressure and power coefficient are compared with respect to blade rotational angles and rotating frequencies of the turbine blade. Throughout the comparisons of three grid systems, it is noted that the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid has a stable performance compared to the other ones.