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  • AMS(MOS): 65N30  (57)
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  • Mathematics  (57)
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  • Articles  (57)
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  • Mathematics  (57)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 50 (1986), S. 697-721 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary We consider a mixed finite element approximation of the stationary, incompressible Navier-Stokes equations with slip boundary condition, which plays an important rôle in the simulation of flows with free surfaces and incompressible viscous flows at high angles of attack and high Reynold's numbers. The central point is a saddle-point formulation of the boundary conditions which avoids the well-known Babuška paradox when approximating smooth domains by polyhedrons. We prove that for the new formulation one can use any stable mixed finite element for the Navier-Stokes equations with no-slip boundary condition provided suitable bubble functions on the boundary are added to the velocity space. We obtain optimal error estimates under minimal regularity assumptions for the solution of the continous problem. The techniques apply as well to the more general Navier boundary condition.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 52 (1987), S. 81-99 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G 1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary The slow viscous flow past a spatial body with corners and edges is investigated mathematically and numerically by means of a boundary element method. For the resulting algebraic system a multigrid solver is designed and analyzed. Due to an improved bound on the rate of convergence it proves to be preferable to that introduced earlier for related problems. A numerical example illustrates some of the proposed methods.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 52 (1988), S. 147-163 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary Finite element approximation of a nonlinear elliptic pseudomonotone second-order boundary value problem in a bounded nonpolygonal domain Ω with mixed Dirichlet-Neumann boundary conditions is studied. In the discretization we approximate the domain Ω by a polygonal one, use linear conforming triangular elements and evaluate integrals by numerical quadratures. We prove the solvability of the discrete problem and on the basis of compactness properties of the corresponding operator (which is not monotone in general) we prove the convergence of approximate solutions to an exact weak solutionu∈H 1 Ω). No additional assumption on the regularity of the exact solution is needed.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 50 (1987), S. 557-565 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary Almost optimalL ∞-convergence of an approximation of a variational inequality of parabolic type is proved under regularity assumptions which are met by the solution of a one phase Stefan problem. The discretization employs piecewise linear finite elements in space and the backward Euler scheme in time. By means of a maximum principle the problem is reduced to an error estimate for an auxiliary parabolic equation. The latter bound is obtained by using the smoothing property of the Galerkin method.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 51 (1987), S. 87-101 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary We solve the Helmholtz equation in an exterior domain in the plane. A perfect absorption condition is introduced on a circle which contains the obstacle. This boundary condition is given explicitly by Bessel functions. We use a finite element method in the bounded domain. An explicit formula is used to compute the solution out of the circle. We give an error estimate and we present relevant numerical results.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 51 (1987), S. 237-250 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary Two families of mixed finite elements, one based on simplices and the other on cubes, are introduced as alternatives to the usual Raviart-Thomas-Nedelec spaces. These spaces are analogues of those introduced by Brezzi, Douglas, and Marini in two space variables. Error estimates inL 2 andH −s are derived.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 97-105 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary Lagrangian formulations for the Cauchy problems for the generalized-heat and porous-media equations are introduced and equivalence and existence results discussed. Efficient interface tracking finite difference and finite element discretizations of the Lagrangian formulation are discussed. Mixed Euler-Lagrange formulations for mixed problems and the one phase Stefan problem are presented. Numerical experiments are discussed.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 199-224 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G 1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary The problems of elliptic partial differential equations stemming from engineering problems are usually characterized by piecewise analytic data. It has been shown in [3, 4, 5] that the solutions of the second order and fourth order equations belong to the spacesB β 1 where the weighted Sobolev norms of thek-th derivatives are bounded byCd k−l (k−l)!,k≧l, l≦2 whereC andd are constants independent ofk. In this case theh−p version of the finite element method leads to an exponential rate of convergence measured in the energy norm [6, 12, 13]. Theh−p version was implemented in the code PROBE1 [18] and has been very successfully used in the industry. We will discuss in this paper the generalization of these results for problems of order2m. We will show also that the exponential rate can be achieved if the exact solution belongs to the spacesB β 1 where the weighted Sobolev norm of thek-th derivatives is bounded byCd k−l (k−l)!,k≧l=m+1, C andd are independent ofk. In addition, if the data is piecewise analytic, then in fact the exact solution belongs to the spacesB β m+1 . Problems of this type are related obviously to many engineering problems, such as problems of plates and shells, and are also important in connection with well-known locking problems.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 315-349 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G.1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Description / Table of Contents: Résumé L'objet de cet article consiste en une approximation d'une variante des équations de mouvement stationnaire d'un fluide incompressible de troisième grade, en dimension 2: $$\begin{gathered} - v\Delta u + rot(u - \alpha _1 \Delta u) \wedge u - (\alpha _1 + \alpha _2 )(A\Delta u + 2 div(\nabla u\nabla u^T )) \hfill \\ - \beta div(|A|^2 A) + \nabla p + \varepsilon \Delta ^2 u = f, \hfill \\ divu = 0, \hfill \\ \end{gathered}$$ qui sont une généralisation des équations de Navier-Stokes. Dans une première partie, on donne une caractérisation fondamentale de l'espaceV [Hm(Ω)]n , oùV={υ∈[D(Ω)] n ], div υ=0}. On étudie ensuite, dans une seconde partie, une approximation mixte du problème linéaire associé: $$\begin{gathered} - v\Delta u + \varepsilon \Delta ^2 u + \nabla p = f, \hfill \\ div u = 0. \hfill \\ \end{gathered}$$ Les résultats obtenus sont utilisés dans la dernière partie consacrée à une méthode d'approximation mixte de notre problème. La méthode de Taylor-Hood nous permet enfin d'obtenir des applications aux éléments finis de degré 2.
    Notes: Summary This paper is concerned with the approximation of a variant of the steady state, two-dimensional equations of an incompressible fluid of grade three: $$\begin{gathered} - v\Delta u + rot(u - \alpha _1 \Delta u) \wedge u - (\alpha _1 + \alpha _2 )(A\Delta u + 2 div(\nabla u\nabla u^T )) \hfill \\ - \beta div(|A|^2 A) + \nabla p + \varepsilon \Delta ^2 u = f, \hfill \\ divu = 0, \hfill \\ \end{gathered}$$ which generalize the Navier-Stokes equations. The first part gives a fundamental characterization of the closure ofV={υ∈[D(Ω)] n ], div υ=0} in [H m (Ω)] n . Next, the second part studies a mixed approximation of the underlying linear problem: $$\begin{gathered} - v\Delta u + \varepsilon \Delta ^2 u + \nabla p = f, \hfill \\ div u = 0. \hfill \\ \end{gathered}$$ The results obtained are then extended in the third part to our non-linear problem. The Hood-Taylor finite element method provides a specific application to finite elements of degree two.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 56 (1989), S. 827-838 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary We introduce a way of using the mixed finite element families of Raviart, Thomas and Nedelec [13, 14], and Brezzi et al. [5–7], for constructing stable and optimally convergent discretizations for the Stokes problem.
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