• Title, Summary, Keyword: Finite Element Approximation

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Approximation Method for the Calculation of Stress Intensity Factors for the Semi-elliptical Surface Flaws on Thin-Walled Cylinder

  • Jang Chang-Heui
    • Journal of Mechanical Science and Technology
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    • v.20 no.3
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    • pp.319-328
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    • 2006
  • A simple approximation method for the stress intensity factor at the tip of the axial semielliptical cracks on the cylindrical vessel is developed. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. For these, 3-D finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R=0.1. The approximation solutions are within $\pm2.5%$ of the those of finite element analysis using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the approximation method provides sufficiently accurate stress intensity factor values for the axial semi-elliptical flaws on the surface of the reactor pressure vessel.

MLS-Based Finite Elements and a Proposal for Their Applications (MLS기반 유한요소와 그 응용에 관한 제언)

  • Cho, Young-Sam
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.22 no.4
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    • pp.335-341
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    • 2009
  • In this paper, review of developed MLS-based finite elements and a proposal for their applications are described. The shape functions and their derivatives of MLS-based finite elements are constructed using Moving-Least Square approximation. In MLS-based finite element, using the adequate influence domain of weight function used in MLS approximation, kronecker delta condition could be satisfied at the element boundary. Moreover, because of the characteristics of MLS approximation, we could easily add extra nodes at an arbitrary position in MLS-based finite elements. For these reasons, until now, several variable-node elements(2D variable element for linear case and quadratic case and 3D variable-node elements) and finite crack elements are developed using MLS-based finite elements concept. MLS-based finite elements could be extended to 2D variable-node triangle element, 2D finite crack triangle element, variable-node shell element, finite crack shell element, and 3D polyhedron element. In this paper, we showed the feasibility of 3D polyhedron element at the case of femur meshing.

New higher-order triangular shell finite elements based on the partition of unity

  • Jun, Hyungmin
    • Structural Engineering and Mechanics
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    • v.73 no.1
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    • pp.1-16
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    • 2020
  • Finite elements based on the partition of unity (PU) approximation have powerful capabilities for p-adaptivity and solutions with high smoothness without remeshing of the domain. Recently, the PU approximation was successfully applied to the three-node shell finite element, properly eliminating transverse shear locking and showing excellent convergence properties and solution accuracy. However, the enrichment with the PU approximation results in a significant increase in the number of degrees of freedom; therefore, it requires greater computational cost, thus making it less suitable for practical engineering. To circumvent this disadvantage, we propose a new strategy to decrease the total number of degrees of freedom in the existing PU-based shell element, without loss of optimal convergence and accuracy. To alleviate the locking phenomenon, we use the method of mixed interpolation of tensorial components and perform convergence studies to show the accuracy and capability of the proposed shell element. The excellent performances of the new shell elements are illustrated in three benchmark problems.

MIXED FINITE VOLUME METHOD ON NON-STAGGERED GRIDS FOR THE SIGNORINI PROBLEM

  • Kim, Kwang-Yeon
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.12 no.4
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    • pp.249-260
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    • 2008
  • In this work we propose a mixed finite volume method for the Signorini problem which are based on the idea of Keller's finite volume box method. The triangulation may consist of both triangles and quadrilaterals. We choose the first-order nonconforming space for the scalar approximation and the lowest-order Raviart-Thomas vector space for the vector approximation. It will be shown that our mixed finite volume method is equivalent to the standard nonconforming finite element method for the scalar variable with a slightly modified right-hand side, which are crucially used in a priori error analysis.

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AN ASYMPTOTIC FINITE ELEMENT METHOD FOR SINGULARLY PERTURBED HIGHER ORDER ORDINARY DIFFERENTIAL EQUATIONS OF CONVECTION-DIFFUSION TYPE WITH DISCONTINUOUS SOURCE TERM

  • Babu, A. Ramesh;Ramanujam, N.
    • Journal of applied mathematics & informatics
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    • v.26 no.5_6
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    • pp.1057-1069
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    • 2008
  • We consider singularly perturbed Boundary Value Problems (BVPs) for third and fourth order Ordinary Differential Equations(ODEs) of convection-diffusion type with discontinuous source term and a small positive parameter multiplying the highest derivative. Because of the type of Boundary Conditions(BCs) imposed on these equations these problems can be transformed into weakly coupled systems. In this system, the first equation does not have the small parameter but the second contains it. In this paper a computational method named as 'An asymptotic finite element method' for solving these systems is presented. In this method we first find an zero order asymptotic approximation to the solution and then the system is decoupled by replacing the first component of the solution by this approximation in the second equation. Then the second equation is independently solved by a fitted mesh Finite Element Method (FEM). Numerical experiments support our theoritical results.

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POSTPROCESSING FOR THE RAVIART-THOMAS MIXED FINITE ELEMENT APPROXIMATION OF THE EIGENVALUE PROBLEM

  • Kim, Kwang-Yeon
    • Korean Journal of Mathematics
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    • v.26 no.3
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    • pp.467-481
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    • 2018
  • In this paper we present a postprocessing scheme for the Raviart-Thomas mixed finite element approximation of the second order elliptic eigenvalue problem. This scheme is carried out by solving a primal source problem on a higher order space, and thereby can improve the convergence rate of the eigenfunction and eigenvalue approximations. It is also used to compute a posteriori error estimates which are asymptotically exact for the $L^2$ errors of the eigenfunctions. Some numerical results are provided to confirm the theoretical results.

Applications of MLS(Moving Least Sqrare)-based Finite Elements for Mechanics Problems Involving Interfaces and Discontinuities (경계 및 불연속의 해결을 위한 이동최소제곱 기반 유한요소의 적용)

  • Lim Jae-Hyuk;Im Se-Young;Cho Young-Sam
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.567-574
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    • 2006
  • We present applications of MLS-based finite elements, which enable us to easily treat highly complex nonmatching finite element meshes and discontinuities. The shape functions of MLS-based finite element can be easily generated with the aid of Moving Least Square approximation on the parental domain. The major advantage includes that the position of element nodes as well as the number of the element nodes can be conveniently adjusted according to the nature of the problems under consideration, so that finite-element mesh is straightforwardly adapted to evolving discontinuities and. interfaces. Furthermore, we show that the present MLS-based finite elements are efficiently applied for elastic-plastic deformations, wherein the implicit constraint of incompressibility should be properly handled.

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Multi-scale finite element analysis of acoustic waves using global residual-free meshfree enrichments

  • Wu, C.T.;Hu, Wei
    • Interaction and multiscale mechanics
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    • v.6 no.2
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    • pp.83-105
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    • 2013
  • In this paper, a multi-scale meshfree-enriched finite element formulation is presented for the analysis of acoustic wave propagation problem. The scale splitting in this formulation is based on the Variational Multi-scale (VMS) method. While the standard finite element polynomials are used to represent the coarse scales, the approximation of fine-scale solution is defined globally using the meshfree enrichments generated from the Generalized Meshfree (GMF) approximation. The resultant fine-scale approximations satisfy the homogenous Dirichlet boundary conditions and behave as the "global residual-free" bubbles for the enrichments in the oscillatory type of Helmholtz solutions. Numerical examples in one dimension and two dimensional cases are analyzed to demonstrate the accuracy of the present formulation and comparison is made to the analytical and two finite element solutions.

A POSTERIORI L(L2)-ERROR ESTIMATES OF SEMIDISCRETE MIXED FINITE ELEMENT METHODS FOR HYPERBOLIC OPTIMAL CONTROL PROBLEMS

  • Hou, Tianliang
    • Bulletin of the Korean Mathematical Society
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    • v.50 no.1
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    • pp.321-341
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    • 2013
  • In this paper, we discuss the a posteriori error estimates of the semidiscrete mixed finite element methods for quadratic optimal control problems governed by linear hyperbolic equations. The state and the co-state are discretized by the order $k$ Raviart-Thomas mixed finite element spaces and the control is approximated by piecewise polynomials of order $k(k{\geq}0)$. Using mixed elliptic reconstruction method, a posterior $L^{\infty}(L^2)$-error estimates for both the state and the control approximation are derived. Such estimates, which are apparently not available in the literature, are an important step towards developing reliable adaptive mixed finite element approximation schemes for the control problem.

Finite 'crack' element method (균열 유한 요소법)

  • Cho, Young-Sam;Jun, Suk-Ky;Im, Se-Young
    • Proceedings of the KSME Conference
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    • pp.551-556
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    • 2004
  • We propose a 2D 'crack' element for the simulation of propagating crack with minimal remeshing. A regular finite element containing the crack tip is replaced with this novel crack element, while the elements which the crack has passed are split into two transition elements. Singular elements can easily be implemented into this crack element to represent the crack-tip singularity without enrichment. Both crack element and transition element proposed in our formulation are mapped from corresponding master elements which are commonly built using the moving least-square (MLS) approximation only in the natural coordinate. In numerical examples, the accuracy of stress intensity factor $K_I$ is demonstrated and the crack propagation in a plate is simulated.

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