• Title, Summary, Keyword: finite order

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On the Design of a Finite Time Reduced Order Observer (유한시간 감소차수 관측자의 설계)

  • Lee, Kee-Sang
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.59 no.5
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    • pp.961-965
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    • 2010
  • A reduced order observer with finite time convergence characteristics is proposed for linear time invariant systems. The proposed finite time reduced order observer(FTROO) is a dual observer scheme in which two reduced order Luenberger observers with asymptotic convergence characteristics and a finite time delay element are employed. The FTROO can be constructed so as to converge in the designer specified finite time independent of the eigenvalues of the reduced order observers. A numerical example is given to show the finite-time convergence characteristics of the proposed FTROO.

Improving the eigenvalue using higher order elements without re-solving

  • Stephen, D.B.;Steven, G.P.
    • Structural Engineering and Mechanics
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    • v.5 no.4
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    • pp.385-398
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    • 1997
  • High order finite element have a greater convergence rate than low order finite elements, and in general produce more accurate results. These elements have the disadvantage of being more computationally expensive and often require a longer time to solve the finite element analysis. High order elements have been used in this paper to obtain a new eigenvalue solution with out re-solving the new model. The optimisation of the eigenvalue via the differentiation of the Rayleigh quotient has shown that the additional nodes associated with the higher order elements can be condensed out and solved using the original finite element solution. The higher order elements can then be used to calculate an improved eigenvalue for the finite element analysis.

A fourth order finite difference method applied to elastodynamics: Finite element and boundary element formulations

  • Souza, L.A.;Carrer, J.A.M.;Martins, C.J.
    • Structural Engineering and Mechanics
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    • v.17 no.6
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    • pp.735-749
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    • 2004
  • This work presents a direct integration scheme, based on a fourth order finite difference approach, for elastodynamics. The proposed scheme was chosen as an alternative for attenuating the errors due to the use of the central difference method, mainly when the time-step length approaches the critical time-step. In addition to eliminating the spurious numerical oscillations, the fourth order finite difference scheme keeps the advantages of the central difference method: reduced computer storage and no requirement of factorisation of the effective stiffness matrix in the step-by-step solution. A study concerning the stability of the fourth order finite difference scheme is presented. The Finite Element Method and the Boundary Element Method are employed to solve elastodynamic problems. In order to verify the accuracy of the proposed scheme, two examples are presented and discussed at the end of this work.

ERROR ESTIMATES OF MIXED FINITE ELEMENT APPROXIMATIONS FOR A CLASS OF FOURTH ORDER ELLIPTIC CONTROL PROBLEMS

  • Hou, Tianliang
    • Bulletin of the Korean Mathematical Society
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    • v.50 no.4
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    • pp.1127-1144
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    • 2013
  • In this paper, we consider the error estimates of the numerical solutions of a class of fourth order linear-quadratic elliptic optimal control problems by using mixed finite element methods. The state and co-state are approximated by the order $k$ Raviart-Thomas mixed finite element spaces and the control variable is approximated by piecewise polynomials of order $k(k{\geq}1)$. $L^2$ and $L^{\infty}$-error estimates are derived for both the control and the state approximations. These results are seemed to be new in the literature of the mixed finite element methods for fourth order elliptic control problems.

Analysis of composite plates using various plate theories -Part 2: Finite element model and numerical results

  • Bose, P.;Reddy, J.N.
    • Structural Engineering and Mechanics
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    • v.6 no.7
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    • pp.727-746
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    • 1998
  • Finite element models and numerical results are presented for bending and natural vibration using the unified third-order plate theory developed in Part 1 of this paper. The unified third-order theory contains the classical, first-order, and other third-order plate theories as special cases. Analytical solutions are developed using the Navier and L$\acute{e}$vy solution procedures (see Part 1 of the paper). Displacement finite element models of the unified third-order theory are developed herein. The finite element models are based on $C^0$ interpolation of the inplane displacements and rotation functions and $C^1$ interpolation of the transverse deflection. Numerical results of bending and natural vibration are presented to evaluate the accuracy of various plate theories.

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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A Generalized Finite Difference Method for Solving Fokker-Planck-Kolmogorov Equations

  • Zhao, Li;Yun, Gun Jin
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.4
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    • pp.816-826
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    • 2017
  • In this paper, a generalized discretization scheme is proposed that can derive general-order finite difference equations representing the joint probability density function of dynamic response of stochastic systems. The various order of finite difference equations are applied to solutions of the Fokker-Planck-Kolmogorov (FPK) equation. The finite difference equations derived by the proposed method can greatly increase accuracy even at the tail parts of the probability density function, giving accurate reliability estimations. Compared with exact solutions and finite element solutions, the generalized finite difference method showed increasing accuracy as the order increases. With the proposed method, it is allowed to use different orders and types (i.e. forward, central or backward) of discretization in the finite difference method to solve FPK and other partial differential equations in various engineering fields having requirements of accuracy or specific boundary conditions.

Analysis of composite steel-concrete beams using a refined high-order beam theory

  • Lezgy-Nazargah, M.;Kafi, L.
    • Steel and Composite Structures
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    • v.18 no.6
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    • pp.1353-1368
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    • 2015
  • A finite element model is presented for the analysis of composite steel-concrete beams based on a refined high-order theory. The employed theory satisfies all the kinematic and stress continuity conditions at the layer interfaces and considers effects of the transverse normal stress and transverse flexibility. The global displacement components, described by polynomial or combinations of polynomial and exponential expressions, are superposed on local ones chosen based on the layerwise or discrete-layer concepts. The present finite model does not need the incorporating any shear correction factor. Moreover, in the present $C^1$-continuous finite element model, the number of unknowns is independent of the number of layers. The proposed finite element model is validated by comparing the present results with those obtained from the three-dimensional (3D) finite element analysis. In addition to correctly predicting the distribution of all stress components of the composite steel-concrete beams, the proposed finite element model is computationally economic.

Lp error estimates and superconvergence for finite element approximations for nonlinear parabolic problems

  • LI, QIAN;DU, HONGWEI
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.4 no.1
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    • pp.67-77
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    • 2000
  • In this paper we consider finite element mathods for nonlinear parabolic problems defined in ${\Omega}{\subset}R^d$ ($d{\leq}4$). A new initial approximation is taken. Optimal order error estimates in $L_p$ for $2{\leq}p{\leq}{\infty}$ are established for arbitrary order finite element. One order superconvergence in $W^{1,p}$ for $2{\leq}q{\leq}{\infty}$ are demonstrated as well.

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