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  • AMS(MOS): 65N30  (11)
  • 1995-1999
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  • 1988  (11)
  • Mathematics  (11)
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  • Articles  (11)
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  • 1995-1999
  • 1985-1989  (11)
  • 1950-1954
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  • Mathematics  (11)
  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; 6D05 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary This paper discusses the computation of multiple solutions of various discretizations of the steady state incompressible Navier-Stokes equations. Solution paths (α,R) satisfying the discrete system of equationsH(α,R)=0, where α represents the discrete flow field andR is the Reynolds number, are computed using a pseudo arc-length continuation procedure. For flows over the back end of an axially symmetric body with a cusped tail in a coaxial circular cylinder, the solution paths often exhibit “hairpin” turning points. Dependence of the paths on the mesh spacing and various selections for the discretizations of the convective and diffusive terms are presented.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 225-235 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary The solution of the Stokes problem is approximated by three stabilized mixed methods, one due to Hughes, Balestra, and Franca and the other two being variants of this procedure. In each case the bilinear form associated with the saddle-point problem of the standard mixed formulation is modified to become coercive over the finite element space. Error estimates are derived for each procedure.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 701-738 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary In this paper, we propose an algorithm to derive nodal methods corresponding to various two and three-dimensional nonconforming and mixed finite elements. We show that this algorithm can be used to obtain several classical schemes as well as some more recently developed schemes, and that it leads to a simple proof of unisolvence for these methods. Finally we use our method to obtain a three dimensional nodal scheme of BDM type.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 13-30 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; 73C35 ; 73K25 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary We propose a new mixed variational formulation for the equations of linear elasticity. It does not require symmetric tensors and consequently is easy to discretize by adapting mixed finite elements developed for scalar second order elliptic equations.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 299-314 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary Here we analyse the boundary element Galerkin method for two-dimensional nonlinear boundary value problems governed by the Laplacian in an interior (or exterior) domain and by highly nonlinear boundary conditions. The underlying boundary integral operator here can be decomposed into the sum of a monotoneous Hammerstein operator and a compact mapping. We show stability and convergence by using Leray-Schauder fixed-point arguments due to Petryshyn and Nečas. Using properties of the linearised equations, we can also prove quasioptimal convergence of the spline Galerkin approximations.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 52 (1988), S. 187-217 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; 73K10 ; 73K15 ; 73K25 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary In this paper, we study the approximation of a right circular cylindrical shell by a nonconforming method using Clough-Johnson flat plate finite elements. Compatibility conditions which have to be satisfied by the degrees of freedom at every node of the triangulation are given. Then, we prove that convergence is insured for shallow shells when using particular families of triangulations which are practically easy to implement. Finally, we propose a new approximation method by flat plate finite elements which assures the convergence for any kind of circular cylindrical shell.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 53 (1988), S. 51-95 
    ISSN: 0945-3245
    Keywords: AMS(MOS): 65N30 ; CR: G1.8
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary In two-dimensional elasticity stresses at reentrant corners exhibit singular behavior. The stress field is of the form $$\sigma = \Sigma {\rm K}_\iota r^{\lambda _2 - 1} f_i (\theta ;\lambda _i )$$ , where (r, θ) are polar coordinates centered at the tip of the corner, andf i (θ;λ i are smooth functions. For practical use of this series the eigenvaluesλ i (which are generally complex numbers) are required in order of ascending real part. The problem then is to find the roots of a transcendental equation (eigenequation) in the complex plane and arranged in order of ascending real part. A theorem is proved on the number, location and nature of the roots of this equation with the real part in fixed intervals of length π. Excellent initial estimates of the real part of the complex roots become available, and so are bounds, within which single real roots exist. This enables the determination of any number of roots in ascending order of real part. The critical angles at which the eigenvalues change nature are also determined. It is shown that for certain cases and for the symmetric mode of deformation, the eigenvalue λ=1 does not represent a rigid body rotation, therefore it has to be included in the series representation of the stresses. The coefficientsK i can be determined by recently developed extraction techniques, thus allowing complete determination of the elastic field and enabling its correlation with experimental data on brittle fracture, crack initiation, plastic zone estimation etc.
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