• 한국정밀공학회지
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• 제22권2호
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• pp.79-88
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• 2005

Evaluating the effective properties of materials containing various types of in-homogeneities is an important issue in the analysis of structures composed of those materials. A simple and effective method for the purpose is to impose the periodic displacement boundary conditions on the finite element model of a unit cell. Their theoretical background is explained based on the purely kinematical relations in the regularly spaced in-homogeneity problems, and the strategies to implement them into the analysis and to evaluate the homogenized material constants are introduced. The creep behavior of a thin sheet with square arrayed rectangular voids is characterized, where the orthotropy is induced by the presence of the voids. The homogenization method is validated through the comparison of the analysis of detailed model with that of the simplified one with the effective parameters.

• 한국정밀공학회지
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• 제21권1호
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• pp.181-188
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• 2004

Structural analysis for materials containing regularly spaced in-homogeneities is usually executed by using averaged material properties. For the homogenization process, a unit cell is defined and loaded somehow, and its response is investigated to evaluate the properties. The imposed loading conditions should accord to the behavior of unit cell immersed in the macroscopic structure in order to guarantee the accuracy of the effective properties. Each unit cell shows periodic variation of strain if the material is loaded uniformly, and in this study, direct implementation of this characteristic behavior is attempted on FE models of unit cell. Conventional finite element analysis tool can be used without any modification, and the boundary of unit cell is constrained in a way that the periodicity is satisfied. The proposed method is applicable to skew arrayed in-homogeneity problems. The flexibility matrix relating tonsorial stress and strain components in skewed rectilinear coordinate system is transformed so that the required engineering constants can be evaluated. Effective properties are computed for the materials with square and skew arrayed circular holes, and its accuracy is examined.

• 대한기계학회논문집B
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• 제37권5호
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• pp.441-448
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• 2013

본 논문에서는 조밀한 계수행렬로 인해 경계요소 개수의 증가에 따른 계산 시간의 급격한 증가때문에 대규모 문제를 쉽게 다룰 수 없는 기존 BEM 문제를 획기적으로 개선하는 새로운 BEM 해법인 FM-BEM을 소개한다. 단순한 2차원 정상상태 열전도문제를 통해서 FM-BEM과 기존 BEM의 계산시간과 정확도에 대한 해석 결과를 제시하였으며, 이로부터 FM-BEM 해법이 기존 BEM과 유사한 정확도를 유지하면서도 계산 속도를 획기적으로 높인다는 결과를 확인하였다. 결과적으로 본 연구에서는 FM-BEM의 적용 이론 및 관련 실행 알고리즘들을 고찰하고 이를 통해서 FM-BEM의 효용성을 검증하였으며, 향후 다양한 공학적 문제로의 적용 범위를 확대하고자 한다.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1540-1546
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• 2000

Recently, force measurement systems are commonly used in many industrial fields and the precision of the measurement system is getting more important as the industry needs more precise tools and in struments to make high quality products. However, a high precision force measurement system is hard to make unless we know precisely the causes, quality and quantity of measurement errors in advance. In this work, many possible mechanical causes of measurement errors are reviewed including ratio of length to diameter of sensing part, radius of contact area, radius of bearing part, ratio of material properties and change of boundary conditions. Also, the measurement errors are analyzed by nonlinear finite element method and the nonlinear behavior of the errors are investigated. The results can be used to design force measurement systems and expected to be very useful especially for compact type load cells.

• Journal of applied mathematics & informatics
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• 제31권5_6호
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• pp.695-709
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• 2013

Calcium is well known role for signal transduction in a neuron cell. Various processes and parameters modulate the intracellular calcium signaling process. A number of experimental and theoretical attempts are reported in the literature for study of calcium signaling in neuron cells. But still the role of various processes, components and parameters involved in calcium signaling is still not well understood. In this paper an attempt has been made to develop two dimensional finite element model to study calcium diffusion in neuron cells. The JRyR, JSERCA and JLeak, the exogenous buffers like EGTA and BAPTA, and diffusion coefficients have been incorporated in the model. Appropriate boundary conditions have been framed. Triangular ring elements have been employed to discretized the region. The effect of these parameters on calcium diffusion has been studied with the help of numerical results.

• Journal of the Korean Wood Science and Technology
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• 제42권2호
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• pp.138-146
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• 2014

Stem and root of Lindera erythrocarpa were described and compared in the wood anatomical aspects. Root wood appeared to differ from stem wood in the qualitative features of growth ring boundary, extraneous materials in vessel element and ray parenchyma cell, outline of ray, and sheath cell. In the quantitative features, there were differences between these two tissues in vessels per square millimeter, tangential diameter of vessel lumina, length of vessel element, and width of ray. These wood anatomical differences between stem above ground and root below ground were thought to be attributed to their different growth environments.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.347-352
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• 2005

Scan Element Pattern(SEP) and Scan Impedance(SI) concepts are used to analyze the characteristics of open-ended waveguide array, which is the representative phased array antenna element in C-band and X-band. Transmit SEP's are calculated for 15$\sim$15 subarray and SI's are obtained by applying periodic boundary conditions for a unit cell of the given array condition. CST's MWS and Ansoft's HFSS are utilized for each analysis. Some relations are reviewed between the two results, which are based on mutual coupling effects. For validation purpose, an 8$\sim$8 subarray is constructed and tested. Transmit SEP measured in MTG's far-field range shows good agreement with the calculated transmit SEP.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.64-76
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• 2003

In this work, a new penalty formulation is proposed for the analysis of Mindlin-Reissner plates by using the element-free Galerkin method. A penalized weak form for the Mindlin-Reissner Plates is constructed through the exterior penalty method to enforce the essential boundary conditions of rotations as well as transverse displacements. In the numerical examples, some typical problems of Mindlin-Reissner plates are analyzed, and parametric studies on the order of integration and the size of influence domain are also carried out. The effect of the types of background cells on the accuracy of numerical solutions is observed and a proper type of background cell for obtaining optimal accuracy is suggested. Further, optimal order of integration and basis order of Moving Least Squares approximation are suggested to efficiently handle the irregularly distributed nodes through the triangular type of background cells. From the numerical tests, it is identified that unlike the finite element method, the proposed element-free Galerkin method with penalty technique gives highly accurate solution without shear locking in dealing with Mindlin-Reissner plates.

• Structural Engineering and Mechanics
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• 제43권4호
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• pp.411-437
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• 2012

In this paper, we propose a continuum mechanics based 3-D beam finite element with cross-sectional discretization allowing for warping displacements. The beam element is directly derived from the assemblage of 3-D solid elements, and this approach results in inherently advanced modeling capabilities of the beam element. In the beam formulation, warping is fully coupled with bending, shearing, and stretching. Consequently, the proposed beam elements can consider free and constrained warping conditions, eccentricities, curved geometries, varying sections, as well as arbitrary cross-sections (including thin/thick-walled, open/closed, and single/multi-cell cross-sections). We then study the modeling and predictive capabilities of the beam elements in twisting beam problems according to geometries, boundary conditions, and cross-sectional meshes. The results are compared with reference solutions obtained by analytical methods and solid and shell finite element models. Excellent modeling capabilities and solution accuracy of the proposed beam element are observed.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1555-1569
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• 2000

Numerical simulation of fluid flow with moving free surface has been carried out. For the free surface flow, a VOF(Volume of Fluid)-based algorithm utilizing a fixed grid system has been investigated. In order to reduce numerical smearing at the free surface represented on a fixed grid system, a new free surface tracking algorithm based on the donor-acceptor scheme has been presented. Novel features of the proposed algorithm are characterized as two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby-cell to determine the fluid volume flux at each cell boundary. The proposed algorithm can be easily implemented in any irregular non-uniform grid systems that are usual in finite element method (FEM). Moreover, the proposed algorithm can be extended and applied to the 3-D free surface flow problem without additional efforts. For computation of unsteady incompressible flow, a finite element approximation based on the explicit fractional step method has been adopted. In addition, the SUPG(streamline upwind/Petrov-Galerkin) method has been implemented to deal with convection dominated flows. Combination of the proposed free surface tracking scheme and explicit fractional step formulation resulted in an efficient solution algorithm. Validity of the present solution algorithm was demonstrated from its application to the broken dam and the solitary wave propagation problems.