• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.485-490
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• 2015

This paper presents development of a geometrically nonlinear triangular planar element including rotational degrees of freedom, based on the co-rotational(CR) formulation. The CR formulation is one of the efficient geometrically nonlinear formulations and it is based on the assumptions on small strain and large rotation. In this paper, modified CR formulation is suggested for the developemnt of a triangular planar element. The present development is validated regarding the static and time transient problems. The present results are compared with the results predicted by the previous researchers and those obtained by the existing commercial software.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.264-264
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• 2019

개수로 흐름 해석을 위해 수치모형을 적용할 때 반드시 거쳐야 하는 과정이 격자망을 구성하는 일이다. 불규칙한 형상의 자연수로를 모의할 때 격자망 생성은 쉬운 일이 아니며, 따라서 가시적으로 격자망 생성을 돕고, 격자망의 수정도 용이한 도구가 요구된다. 따라서 본 연구에서는 수심적분된 흐름방정식을 지배방정식으로 하여 개수로 흐름 해석을 용이하게 하고자 그래픽 사용자 인터페이스(GUI)를 개발하였으며, 이를 소개하고자 한다. 격자망은 기본적으로 사각형과 삼각형 요소로 구성될 수 있으며, 유한차분모형 등에서는 정형사각형 격자망을, 유한요소모형에서는 비정형 사각형 및 삼각형 격자망 또는 혼합망을 생성시킬 수 있다. 이산점(scatter points)이나 절점(node points)을 생성하거나 기존의 자료를 불러들여 삼각망 또는 사각망을 형성시킬 수 있으며, 연속선(polylines)을 작성하여 형성된 폐다각형(polygones)을 이용하여 정규 또는 비정규의 삼각망 또는 사각망을 형성시킬 수 있다. 또한 두 점사이를 선형 또는 반원 형태로 편향 정도(biased value)를 설정하여 원하는 개수만큼 나눌 수 있도록 하여, 보다 효율적인 격자형성이 가능토록 하였다. 기존 상용 프로그램에서 작성된 격자를 불러들여 활용 가능하며, 백그라운드 이미지로 지형도나 위성사진을 띄어놓고 이미지 상에서 격자를 형성할 수도 있다. 기본적으로 마우스를 이용하여 화면의 이동, 확대 및 축소와 점, 선, 요소의 생성 및 선택이 가능하다. 본 프로그램은 Qt와 modern OpenGL을 바탕으로 제작되었으며, 마이크로소프트사의 windows 뿐만 아니라 Mac OS, Linux 버전의 설치 파일 작성이 가능하다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.478-484
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• 2003

The electromagnetic wave scattering problems from inhomogeneous material bodies are considered. The formulation is made in terms of mixed potentials for the moment methods (MoM). The surfaces of a three-dimensional inhomogeneous scatterer of arbitrary shape are divide into triangular patches for descretization. Application of the boundary conditions leads to the coupled surface integral equations to be satisfied for the unknown surface equivalent electric and magnetic currents. The radar cross-section (RCS) for some structures is computed and the results are compared with the reported data.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.16 no.2
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• pp.149-158
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• 1998

The aim of this paper is to propose the technique of the two dimensional geodetic coordinates conversion between WGS84 and Bessel spheroids by the two-dimensional affine transformation modeling based on the UTM plane coordinates without the local geoid model which is essential to three dimensional coordinates conversion. Area of approximately $25\times{11}$ square km in the city of Inchon was selected as the test area. The transformation parameters were determined using the eleven triangulation control points in test area. And then, those paraneters were applied to the fifteen cadastral control points which selected as checking points for precision checking of transformation parameters. The average and standard deviations of the absolute values of the conversion residuals of checking points in latitude/longitude and N/E(UTM) and/or x/y(TM) are $\pm0.006"$$\pm0.013"$ and $\pm{17cm/}\pm{30cm}$ respectively. Also, coefficients for 7-parameters, 3-parameters and UTM model transformation computed according as sizes of transformed area, and then the transformed characteristics of checking points according to transformation methods analyzed synthetically.hetically.

• The Mathematical Education
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• v.61 no.1
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• pp.47-62
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• 2022

This study investigated the contents related to the plane figures in the geometry domains of Joseon-Sanhak in the late 18th century and focused on changes in explanations and calculation methods related to plane figures, the rigor of mathematical logic in the problem-solving process, and the newly emerged mathematical topics. For this purpose, We analyzed , and written in the late 18th century and and written in the previous period. The results of this study are as follows. First, an explanation that pays attention to the figures as an object of inquiry, not as a measurement object, and a case of additional presentation or replacing the existing solution method was found. Second, descriptions of the validity of calculations in some problems, explanations through diagrams with figure diagrams, clear perceptions of approximations and explanations of more precise approximation were representative examples of pursuing the rigor of mathematical logic. Lastly, the new geometric domain theme in the late 18th century was Palsun corresponding to today's trigonometric functions and example of extending the relationship between the components of the triangle to a general triangle. Joseon-Sanhak cases in the late 18th century are the meaningful materials which explain the gradual acceptance of the theoretical and argumentative style of Western mathematics

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1041-1050
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• 2011

An elasto-plastic finite element method using the theory of strain gradient plasticity is proposed to evaluate the size dependency of structural plasticity that occurs when the configuration size decreases to micron scale. For this method, we suggest a low-order plane and three-dimensional displacement-based elements, eliminating the need for a high order, many degrees of freedom, a mixed element, or super elements, which have been considered necessary in previous researches. The proposed method can be performed in the framework of nonlinear incremental analysis in which plastic strains are calculated and averaged at nodes. These strains are then interpolated and differentiated for gradient calculation. We adopted a strain-gradient-hardening constitutive equation from the Taylor dislocation model, which requires the plastic strain gradient. The developed finite elements are tested numerically on the basis of typical size-effect problems such as micro-bending, micro-torsion, and micro-voids. With respect to the strain gradient plasticity, i.e., the size effects, the results obtained by using the proposed method, which are simple in their calculation, are in good agreement with the experimental results cited in previously published papers.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.29-38
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• 2015

In this study, track dynamic interaction characteristics caused by the vehicle running through transitional section such as bridge abutments were studied using the finite element analysis program. The geometric condition of track was generated by trigonometric function and allowable maximum track irregularity is determined by KORAIL track maintenance criteria. The sub-infrastructure under rail fastener system was modelled by 3D solid elements. To reduce computational cost only half track line is numerically considered and the roller boundary condition was applied to each side of model. In this study, the vehicle-track dynamic interaction analysis was carried out for standard Korean transition section of concrete track and the dynamic behaviors were investigated. The dynamic characteristics considered are wheel load variation, vertical acceleration at body, and maximum Mises stress at each part of transitional section.