• Title/Summary/Keyword: hexagonal geometry

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다변수 변분해법에 의한 비적합 8절점 육면체 요소 (Incompatible Three-Dimensional Hexagonal Finite Elements by Multivariable Method)

  • 주상백;신효철
    • 대한기계학회논문집A
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    • 제20권7호
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    • pp.2078-2086
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    • 1996
  • This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

Stability of the Pentagon Structure of Water Cluster

  • Yoon, Byoung-Jip;Jhon, Mu-Shik
    • Bulletin of the Korean Chemical Society
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    • 제12권1호
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    • pp.67-70
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    • 1991
  • A hexagonal hexamer of water cluster is optimized by ab initio method using the 4-31G basis set. At this geometry the nonadditive many-body interactions are calculated. The ab initio calculation with large basis set [T. H. Dunning, J. Chem. Phys., 53, 2823 (1970); 54, 3958 (1971)] shows that a pentagonal unit is rather stable among several kinds of clustering units of water molecules.

Three-dimensional numerical analysis of nonlinear phenomena of the tensile resistance of suction caissons

  • Azam, Arefi;Pooria, Ahad;Mehdi, Bayat;Mohammad, Silani
    • Geomechanics and Engineering
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    • 제32권3호
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    • pp.255-270
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    • 2023
  • One of the main parameters that affect the design of suction caisson-supported offshore structures is uplift behavior. Pull-out of suction caissons is profoundly utilized as the offshore wind turbine foundations accompany by a tensile resistance that is a function of a complex interaction between the caisson dimensions, geometry, wall roughness, soil type, load history, pull-out rate, and many other parameters. In this paper, a parametric study using a 3-D finite element model (FEM) of a single offshore suction caisson (SOSC) surrounded by saturated soil is performed to examine the effect of some key factors on the tensile resistance of the suction bucket foundation. Among the aforementioned parameters, caisson geometry and uplift loading as well as the difference between the tensile resistance and suction pressure on the behavior of the soil-foundation system including tensile capacity are investigated. For this purpose, a full model including 3-D suction caisson, soil, and soil-structure interaction (SSI) is developed in Abaqus based on the u-p formulation accounting for soil displacement (u) and pore pressure, P.The dynamic responses of foundations are compared and validated with the known results from the literature. The paper has focused on the effect of geometry change of 3-D SOSC to present the soil-structure interaction and the tensile capacity. Different 3-D caisson models such as triangular, pentagonal, hexagonal, and octagonal are employed. It is observed that regardless of the caisson geometry, by increasing the uplift loading rate, the tensile resistance increases. More specifically, it is found that the resistance to pull-out of the cylinder is higher than the other geometries and this geometry is the optimum one for designing caissons.

Specimen Geometry Effects on Oxidation Behavior of Nuclear Graphite

  • Cho, Kwang-Youn;Kim, Kyung-Ja;Lim, Yun-Soo;Chung, Yun-Joong;Chi, Se-Hwan
    • Carbon letters
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    • 제7권3호
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    • pp.196-200
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    • 2006
  • Graphite has hexagonal closed packing structure with two bonding characteristics of van der Waals bonding between the carbon layers at c axis, and covalent bonding in the carbon layer at a and b axis. Graphite has high tolerant to the extreme conditions of high temperature and neutron irradiations rather than any other materials of metals and ceramics. However, carbon elements easily react with oxygen at as low as 400C. Considering the increasing production of today of hydrogen and electricity with a nuclear reactor, study of oxidation characteristics of graphite is very important, and essential for the life evaluation and design of the nuclear reactor. Since the oxidation behaviors of graphite are dependent on the shapes of testing specimen, critical care is required for evaluation of nuclear reactor graphite materials. In this work, oxidation rate and amounts of the isotropic graphite (IG-110, Toyo Carbon), currently being used for the Koran nuclear reactor, are investigated at various temperature. Oxidation process or principle of graphite was figured out by measuring the oxidation rate, and relation between oxidation rate and sample shape are understood. In the oxidation process, shape effect of volume, surface area, and surface to volume ratio are investigated at $600^{\circ}C$, based on the sample of ASTM C 1179-91.

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Development of a fast reactor multigroup cross section generation code EXUS-F capable of direct processing of evaluated nuclear data files

  • Lim, Changhyun;Joo, Han Gyu;Yang, Won Sik
    • Nuclear Engineering and Technology
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    • 제50권3호
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    • pp.340-355
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    • 2018
  • The methods and performance of a fast reactor multigroup cross section (XS) generation code EXUS-F are described that is capable of directly processing Evaluated Nuclear Data File format nuclear data files. RECONR of NJOY is used to generate pointwise XS data, and Doppler broadening is incorporated by the Gauss-Hermite quadrature method. The self-shielding effect is incorporated in the ultrafine group XSs in the resolved and unresolved resonance ranges. Functions to generate scattering transfer matrices and fission spectrum matrices are realized. The extended transport approximation is used in zero-dimensional calculations, whereas the collision probability method and the method of characteristics are used for one-dimensional cylindrical geometry and two-dimensional hexagonal geometry problems, respectively. Verification calculations are performed first for various homogeneous mixtures and cylindrical problems. It is confirmed that the spectrum calculations and the corresponding multigroup XS generations are performed adequately in that the reactivity errors are less than 50 pcm with the McCARD Monte Carlo solutions. The nTRACER core calculations are performed with the EXUS-F-generated 47 group XSs for the two-dimensional Advanced Burner Reactor 1000 benchmark problem. The reactivity error of 160 pcm and the root mean square error of the pin powers of 0.7% indicate that EXUF-F generates properly the broad-group XSs.

Improvement and verification of the DeCART code for HTGR core physics analysis

  • Cho, Jin Young;Han, Tae Young;Park, Ho Jin;Hong, Ser Gi;Lee, Hyun Chul
    • Nuclear Engineering and Technology
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    • 제51권1호
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    • pp.13-30
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    • 2019
  • This paper presents the recent improvements in the DeCART code for HTGR analysis. A new 190-group DeCART cross-section library based on ENDF/B-VII.0 was generated using the KAERI library processing system for HTGR. Two methods for the eigen-mode adjoint flux calculation were implemented. An azimuthal angle discretization method based on the Gaussian quadrature was implemented to reduce the error from the azimuthal angle discretization. A two-level parallelization using MPI and OpenMP was adopted for massive parallel computations. A quadratic depletion solver was implemented to reduce the error involved in the Gd depletion. A module to generate equivalent group constants was implemented for the nodal codes. The capabilities of the DeCART code were improved for geometry handling including an approximate treatment of a cylindrical outer boundary, an explicit border model, the R-G-B checker-board model, and a super-cell model for a hexagonal geometry. The newly improved and implemented functionalities were verified against various numerical benchmarks such as OECD/MHTGR-350 benchmark phase III problems, two-dimensional high temperature gas cooled reactor benchmark problems derived from the MHTGR-350 reference design, and numerical benchmark problems based on the compact nuclear power source experiment by comparing the DeCART solutions with the Monte-Carlo reference solutions obtained using the McCARD code.

$R-{\theta}$ 좌표계에 의한 원자로 압력용기 차폐해석체계 개발 (Development of Shielding Analysis System for the Reactor Vessel by $R-{\theta}$ Coordinate Geometry)

  • 김하용;구본승;김교윤;이정찬;지성균
    • Journal of Radiation Protection and Research
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    • 제30권1호
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    • pp.39-44
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    • 2005
  • 노심 및 원자로의 구조 및 구성 물질이 확정되어 있지 않은 개발단계의 신형원자로의 압력용기에 대한 $R-{\theta}$좌표에서 차폐해석을 수행하려면, 매번 선원항에 대한 모델작업을 하는데 많은 노력과 시간이 소요된다. 따라서 $R-\theta$좌표에 의한 반경방향의 원자로 압력용기에 대한 차폐해석에 있어서 노심의 기하학적 구조에 영향을 받지 않고 해석할 수 있는 체계를 개발하였다. 개발된 해석체계를 이용하여 육방형 노심배열을 갖는 일체형 원자로의 압력용기에 대한 차폐해석을 수행하여, 그 결과를 MCNP 해석결과와 비교 분석하였다. 분석결과 개발된 해석체계가 좀 더 보수적인 결과를 나타내었으며 이는 차폐해석측면에서 타당하다. 또한 이 해석체계를 개발함으로써 그 동안 수작업으로 작성하였던 노심내부에 대한 모델에 대한 오차를 줄일 수 있으며 이에 소요되는 시간 및 노력을 줄일 수 있을 것으로 판단된다.

비축대칭 압출 공정의 유한 요소 해석 (Finite Element Analysis of the Non-axisymmetric Extrusion Process)

  • 신현우
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 1992년도 춘계학술대회 논문집 92
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    • pp.27-46
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    • 1992
  • In this study a new simplified three-dimensional numerical method and the associated computer program have been developed to simulate the non-axisymmetric extrusion processes. The two-dimensional rigid-plastic finite element method under the generalized plane-strain condition, is combined with the slab method. To define the die geometry for non-axisymmetric extrusion, area mapping technique was used. Streamlined die surface was used to miniminze the total extrusion pressure. Extrusion of square, hexagonal and "T" section from round billet have been simulated and experimented with a model material. The computed results were in good agreement with the experiments in cross-sectional grid distortion. Computational results will be valuable for designing tool geometries and corresponding processes.

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Electric Field Effect on Nanochannel Formation in Electrochemical Porous Structures of Alumina

  • Kim, Keun-Joo;Choi, Jae-Ho;Lee, Jung-Tack
    • Transactions on Electrical and Electronic Materials
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    • 제11권5호
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    • pp.230-233
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    • 2010
  • The authors investigated the anodization mechanism of aluminum in an oxalic acid solution, and the electrochemical reaction is very unique for pore formation via the dissolution process, which is very dependent on the surface geometry in nanoporous alumina templates. The cross-sectional nanochannels showed that the geometrical curvature of the initial surface can cause the branching of nanochannels to be adjusted in volume occupancy to be direct to the electric field normal to the surface. The nanoporous alumina with the crystalline $\gamma-Al_2O_3$ phase showed hexagonal ordering at a voltage of 40 V, with a nanohole distance of 102 nm from the charge density oscillation of the oxalic acid solution.

비축대칭 압출 공정의 근사 3차원 유한 요소 해석 (A Simplified Three-Dimensional Finite Element Analysis of the Non-axisymmetric Extrusion Process)

  • 신현우;김동원;김낙수
    • 소성∙가공
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    • 제1권1호
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    • pp.52-65
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    • 1992
  • In this study a new simplified three-dimensional numerical method and the associated computer program have been developed to simulate the non-axisymmetric extrusion processes. The two-dimensional rigid-plastic finite element method under the generalized plane-strain condition is combined with the slab method. To define the die geometry for a non-axisymmetric extrusion. area mapping technique was used. Streamlined die surface was used to minimize the total extrusion pressure. Extrusion of square, hexagonal and 'T' section from round billet have been simulated and experimented with a model material. The computed results were in good agreement with the experiments in cross-sectional grid distortion. Computational results will be valuable for designing tool geometries and corresponding processes.

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