• Title/Summary/Keyword: 해석적 적분

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금속 성형 공정의 준정적 변형 예측을 위한 외연적 시간 적분 유한 요소법의 적용성 연구

  • 유요한;양동열
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.04b
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    • pp.192-197
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    • 1995
  • 소재의 손실을 최소한 줄이면서 원하는 형상의 제품을 가공하는 가장 기본적인 금속 가공 방법은 금형을 이용하는 금속 성형(metal forming)이다. 본 논문에서는 준정적 금속 성형 문제 해석 에대한 외연적 시간 적분 유한 요소법의 적용성을 평가 하기 위하여 변형모드가 복잡한 박판튜브 (thin-walled tube)의 좌굴문제를 해석하여 변형과정이 이론 및 실험결과와 비교적 잘 일치하는지 살펴보기로 한다. 또한 준정적 금속 성형 문제 해석에 외연적 시간 적분 유한 요소법을 사용할 때 계산 시간을 줄이기 위하여 많이 사용되는 가압속도 조절법(loading velocity control technique) 의 타당성을 평가하기 위하여 박판 튜브와 중실 실린더(solid cylinder)의 변형 속도에 따른 변형 모드의 변화를 비교 관찰하여 기하학적 형상에따른 가압속도 조절법의 적용 가능 여부를 분석하여 보겠다.

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Derivation of an Asymptotic solution for a Perfect Conducting Wedge by Using the Dual Integral Equation, Part II : H-Polarized Plane Wave Incidence (쌍적분 방정식을 이용한 완전도체쐐기의 점근해 유도, II : H-분극된 평면파 입사시)

  • Ha, Huen-Tae;Ra, Jung-Woong
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.36D no.1
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    • pp.22-28
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    • 1999
  • An exact asymptotic solution for a perfect conducting wedge with H-polarized plane wave incidence is analytically derived by substituting the exact boundary fields of the perfeet conducting wedge, the well known series solution, into the dual integral exquation in the spectral domain. The validity of the derivation is assured by showing that the analytic integration gives the null fields in the complementary region. The merits taking the dual integral equation for derivation of an asymptotic solution for a perfect conduction wedge is discussed.

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Derivation of an Asymptotic solution for a Perfect Conducting Wedge by Using the Dual Integral Equation, Part I : E-Polarized Plane Wave Incidence (쌍적분 방정식을 이용한 완전도체쐐기의 점근해 유도, I : E-분극된 평면파 입사시)

  • 하헌태;나정웅
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.12
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    • pp.21-29
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    • 1998
  • Dual integral equation in the spectral domain is derived for an arbitrary angled perfect conducting wedge with E-polarized plane wave incidence. Analytic integration of the dual integral equation in the spectral domain with the exact boundary fields of the perfect conducting wedge, the well known series solution, gives the exact asymptotic solution. The validity of the integration is assured by showing that analytic integration gives the null fields in the complementary region.

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Analysis of Semi-Infinite Problems Subjected to Body Forces Using Nonlinear Finite Elements and Boundary Elements (물체력이 작용되는 반무한영역문제의 비선형유한요소-경계요소 조합해석)

  • Hwang, Hak Joo;Kim, Moon Kyum;Huh, Taik Nyung;Ra, Kyeong Woong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.11 no.1
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    • pp.45-53
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    • 1991
  • The underground structure, which has infinite or semi-infinite boundary conditions, is subjected by body forces and in-situ stresses. It also has stress concentration, which causes material nonlinear behavior, in the vicinity of the excavated surface. In this paper, some methods which can be used to transform domain integrals into boundary integrals are reviewed in order to analyze the effect of the body forces and the in-situ stresses. First, the domain integral of the body force is transformed into boundary integral by using the Galerkin tensor and divergence theorem. Second, it is transformed by writing the domain integral in cylindrical coordinates and using direct integration. The domain integral of the in-situ stress is transformed into boundary integral applying the direct integral method in cylindrical coordinates. The methodology is verified by comparing the results from the boundary element analysis with those of the finite element analysis. Coupling the above boundary elements with finite elements, the nonlinear behavior that occurs locally in the vicinity of the excavation is analyzed and the results are verified. Thus, it is concluded that the domain integrals of body forces and in-situ stresses could be performed effectively by transforming them into the boundary integrals, and the nonlinear behavior can be reasonably analyzed by coupled nonlinear finite element and boundary element method. The result of this research is expected to he used for the analysis of the underground structures in the effective manner.

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Advanced Finite Element Analysis for Linear Viscoelastic Problems of a Hereditary-Type Constitutive Law (유전적분형 선형 점탄성문제의 유한요소법에 의한 효율적 해석)

  • 심우진;이성희
    • Computational Structural Engineering
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    • v.6 no.2
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    • pp.103-114
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    • 1993
  • An advanced time-domain finite element formulation is presented for the displacement and stress analysis of isotropic, linear viscoelastic problems of a hereditary-type constitutive law. The semidiscrete finite element method with linear time-stepping scheme and an elastic-viscoelastic correspondence principle are used in the theoretical development. An efficient treatment of hereditary integral is introduced to improve the numerical accuracy, to reduce the computation time, and to avoid the use of large memory storage. Two-dimensional numerical examples of plane strain and plane stress are solved under the assumption on the material property of being elastic in dilatation and like three-element Voigt model in distorsion, and compared with the analytical solutions and the past numerical results to show the versatility and efficiency of the proposed method.

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Transient coupled thermoelastic analysis by finite element method (유한요소법에 의한 과도연성 열탄성 해석)

  • 이태원;심우진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.6
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    • pp.1408-1416
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    • 1990
  • A powerful and efficient method for finding approximate solutions to initial-boundary-value problems in the transient coupled thermoelasticity is formulated in time domain using the finite element technique with time-marching strategy. The final system equations can be derived by the Guritin's variational principle using the definition of convolution integral. But, the finite element formulation for the equations of motion is modified by differentiating in time. Numerical results to some test problems are compared with analytical and other sophisticated approximate solutions. Stable responces are observed in all the given examples irrespective of incremental time steps and mesh shapes. In addition, it is shown that good numerical results are obtained even in coarser mesh or larger time step comparing to other numerical methods.

Adaptive Element-free Galerkin Procedures by Delaunay Triangulation (Delaunay 삼각화를 이용한 적응적 Element-free Galerkin 해석)

  • 이계희;정흥진;최창근
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.14 no.4
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    • pp.525-535
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    • 2001
  • In this paper, a new adaptive analysis scheme for element-free Galerkin method(EFGM) is proposed. The novel point of this scheme is that the triangular cell structure based on the Delaunay triangulation is used in the numerical integration and the node adding/removing process. In adaptive analysis with this scheme, there is no need to divide the integration cell and the memory cell structure. For the adaptive analysis of crack propagation, the reconstruction of cell structure by adding and removing the nodes on integration cells based the estimated error should be carried out at every iteration step by the Delaunay triangulation technique. This feature provides more convenient user interface that is closer to the real mesh-free nature of EFGM. The analysis error is obtained basically by calculating the difference between the values of the projected stresses and the original EFG stresses. To evaluate the performance of proposed adaptive procedure, the crack propagation behavior is investigated for several examples.

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Application of p-Version Crack Model Based on J-integral Method in LEFM Analysis (선형탄성 파괴역학해석에서 J-적분법에 의한 p-Version 균열모델의 적용)

  • 이채규;우광성;김영인
    • Computational Structural Engineering
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    • v.8 no.4
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    • pp.137-148
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    • 1995
  • A new path independent contour integral formulus for the distinct calculation of mode I stress intensity factors in two dimensional linear elastic fracture mechanics problems is presented. This method is based on p-convergence concepts and can be easily appended to existing finite element computer codes. In this study, the stress state at crack tip has been investigated and the path independence of J-integral values has been tested with respect to different contours expressed by normalized distance apart from the crack tip. Numerical results by p-convergence for the problems such as centrally cracked panels, single and double edged cracks in rectangular panels have been compared with those by the conventional h-convergence. The comparison demonstrates the accuracy and stability of the proposed method.

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Mean Square Response Analysis of the Tall Building to Hazard Fluctuating Wind Loads (재난변동풍하중을 받는 고층건물의 평균자승응해석)

  • Oh, Jong Seop;Hwang, Eui Jin;Ryu, Ji Hyeob
    • Journal of Korean Society of Disaster and Security
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    • v.6 no.3
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    • pp.1-8
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    • 2013
  • Based on random vibration theory, a procedure for calculating the dynamic response of the tall building to time-dependent random excitation is developed. In this paper, the fluctuating along- wind load is assumed as time-dependent random process described by the time-independent random process with deterministic function during a short duration of time. By deterministic function A(t)=1-exp($-{\beta}t$), the absolute value square of oscillatory function is represented from author's studies. The time-dependent random response spectral density is represented by using the absolute value square of oscillatory function and equivalent wind load spectrum of Solari. Especially, dynamic mean square response of the tall building subjected to fluctuating wind loads was derived as analysis function by the Cauchy's Integral Formula and Residue Theorem. As analysis examples, there were compared the numerical integral analytic results with the analysis fun. results by dynamic properties of the tall uilding.

Implicit Stress Integration of the Generalized Isotropic Hardening Constitutive Model : II . Verification (일반 등방경화 구성관계에 대한 내재적인 음력적분 : II. 검증)

  • 오세붕;이승래
    • Geotechnical Engineering
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    • v.12 no.6
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    • pp.87-100
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    • 1996
  • This paper verifies the accuracy and efficiency of the implicit stress integration algorithm for an anisotropic hardening constitutive model developed in a companion paper[Oh & Lee (1996)3. Simulation of undrained triaxial test results shows the accuracy of the method through an error estimation, and analyses of accuracy and convergence were performed for a numerical excavation problem. As a result, the stress was accurately integrated by the algorithm and the nonlinear solution was converged to be asymptotically quadratic. Furthermore nonlinear FE analysis of a real excavation problem was by performed considering the initial soil conditions and the in-situ construction sequences. The displacements of wall induced by excavation were more accurately estimated by the anisotropic hardening model than by the Cam-clay model.

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