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  • Numerical Methods  (55)
  • 2005-2009
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  • 1
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 10 (1994) 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 2
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 1-19 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We present a new conforming bilinear Petrov-Galerkin finite-element scheme for elliptic transport problems with variable coefficients. This scheme combines a generalized test function and artificial diffusion to achieve O(h4) grid-point accuracy on uniform stencils of 3 × 3 in two dimensions without resorting to the extended stencils of high-order elements. The method is compared with upwind and high-order finite-difference schemes and the standard Galerkin finite-element method for representative test problems. © 1994 John Wiley & Sons, Inc.
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  • 3
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 21-31 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A deformation method of grid generation has been recently proposed. The method is based on Moser's deformation scheme in his study of the volume elements of a Riemannian manifold. In this paper, this deformation method is improved so that the grid adaption takes place according to the physical coordinates. Some numerical results are included to demonstrate the method. © 1994 John Wiley & Sons, Inc.
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  • 4
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 33-63 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: With simple finite-difference operators we construct fourth-order schemes in space and in time for the wave equation, Maxwell equations, and linearized elastodynamic equations using the modified equation approach. The schemes remain stable for arbitrary heterogeneous mediums because the relevant difference operators are always positive definite. We also present some dispersion curves to show the accuracy of the schemes. © 1994 John Wiley & Sons, Inc.
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  • 5
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 65-83 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We develop a model for simulating the growth of a biofilm in a tortuous tube. The solutions to the Navier-Stokes equations and the advection-diffusion equation are calculated numerically using finite differences. These solutions are then coupled with a biofilm growth model. © 1994 John Wiley & Sons, Inc.
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  • 6
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    Numerical Methods for Partial Differential Equations 10 (1994) 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
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  • 7
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 85-101 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new multidomain direct (noniterative) method for solving boundary-value problems is presented. Using this method, the solution is expressed by a linear combination of auxiliary functions and unknowns which pertain to the boundaries of a subdomain. This approach enables us to solve problems independently and exactly, without any iterations between subdomains. As a consequence, different types of equations and coordinate systems may be considered in different subdomains. Moreover, different boundary conditions and variable (in space) time steps may be imposed on the subdomains as well. Applications are given for initial boundary-value problems with known analytical solutions, including a highly nonlinear porosity equation. © 1994 John Wiley & Sons, Inc.
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  • 8
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 10 (1994), S. 103-127 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Through numerical experiments we explore the incremental unknowns method; linear stationary as well as evolutionary problems are considered. For linear stationary problems, the method appears as a nearly optimal two-step preconditioning technique. At each step, we observe that the convergence behavior of the iterative methods employed is dramatically different, depending upon whether or not preconditioning is used. For linear evolutionary problems, successful and sharply accurate long-term integration is observed when the incremental unknowns (other than that of the coarsest level) are, effectively, small quantities. Otherwise, systematical aliasing arises. © 1994 John Wiley & Sons, Inc.
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  • 9
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 129-147 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: L2-error estimates are computed for mixed finite-element methods for second-order quasilinear (and linear, variable coefficient) parabolic equations. Results are given for the continuous-time case. The convergence of the values for both the scalar function and the flux is demonstrated. The technique used here covers the lowest-order Raviart-Thomas spaces, as well as the higher-order spaces. A second paper will present the analysis of a fully discrete scheme. © 1994 John Wiley & Sons, Inc.
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  • 10
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 149-169 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This article treats mixed finite-element methods for second-order quasilinear parabolic equations. A fully discrete scheme is presented and L2-error estimates are established. The convergence of both the function value and the flux is demonstrated. In a previous paper, Part I the author introduced powerful numerical methods for dealing with parabolic problems. The technique used here is an extension of the continuous-time results for the discrete-time case. © 1994 John Wiley & Sons, Inc.
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  • 11
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 171-190 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Coupled and decoupled Taylor-Galerkin algorithms are considered for viscoelastic flow and a model problem - transient startup Poiseuille flow in a channel under a fixed pressure gradient. All algorithms reproduce the steady-state solutions and are stable at high elasticity numbers (E). For a fixed mesh, the coupled and decoupled versions (TGC and TGD) give exceptional time-accuracy at low elasticity numbers [to within O(1%) at E = 1] and reasonable accuracy at high elasticity numbers [to within O(10%) at E = 10, 100]. By definition, the decoupled false-transient scheme (TGF), which uses different time scales for velocity and stress time stepping, provides a poor transient history. Where the main requirement is to compute a steady-state algorithm efficiency is crucial. The TGF scheme attains a steady state between six to eight times faster than does the TGC scheme, and the latter is over twice as fast as the TGD form. © 1994 John Wiley & Sons, Inc.
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  • 12
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 205-223 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The localized adjoint method, when applied using an Eulerian-Lagrangian frame, has been quite successful in treating advection-dominated transport. The resulting methodology is known as ELLAM. In previous work, bilinear functions were used as test functions. In this paper, local constant functions are used instead, leading to procedures which are appealing because, in addition to other advantages of ELLAM methods, they ensure local mass conservation, are easy to apply and can be combined without difficulty with existing solute-transport codes which are based on finite volumes. In addition, the procedures for deriving the algorithms presented here are used as an illustration of a general methodology for treating numerically partial differential equations, which is advocated by the authors. Such methodology consists in identifying the information about the sought solution which is contained in the approximate one and then using this insight to choose the interpolation procedure to be applied. © 1994 John Wiley & Sons, Inc.
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  • 13
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 191-203 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: It is shown that, for a class of time-dependent partial differential equations of the form ut = Lu, one step of the moving finite-element (MFE) procedure corresponds to one iteration of an algorithm for obtaining best L2 fits with adjustable nodes to continuous functions. In the steady-state limit the MFE procedure gives the best fit of Lu, with adjustable nodes, to the null function. For first-order partial differential equations, the MFE procedure moves nodes with approximate characteristic nodal speeds. We identify an additional speed component arising directly from the L2 projection which seeks a best fit in the sense described above. © 1994 John Wiley & Sons, Inc.
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  • 14
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    Numerical Methods for Partial Differential Equations 10 (1994), S. i 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
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  • 15
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    Numerical Methods for Partial Differential Equations 10 (1994) 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
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  • 16
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 225-269 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This article contains a survey of some important finite-difference methods for one-dimensional hyperbolic conservation laws. Weak solutions of hyperbolic conservation laws are introduced and the concept of entropy stability is discussed. Furthermore, the Riemann problem for hyperbolic conservation laws is solved. An introduction to finite-difference methods is given for which important concepts such as, e.g., conservativity, stability, and consistency are introduced. Godunov-type methods are elaborated for general systems of hyperbolic conservation laws. Finally, flux limiter methods are developed for the scalar nonlinear conservation law. © 1994 John Wiley & Sons, Inc.
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  • 17
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 271-294 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Superconvergent error estimates in l2(H1) and l∞(H1) norms are derived for recovered gradients of finite difference in time/piecewise linear Galerkin approximations in space for linear and quasinonlinear parabolic problems in two space dimensions. The analysis extends previous results for elliptic problems to the parabolic context, and covers problems in regions with nonsmooth boundaries under certain assumptions on the regularity of the solutions. © 1994 John Wiley & Sons, Inc.
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  • 18
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 295-308 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Steady incompressible flow around objects in general coordinates is investigated. First, an overview of the popular approaches to discretize incompressible flow problems in general coordinates is given. It has been chosen to solve the equations on a staggered grid with contravariant flux unknowns and pressure as primitive variables. A solution method multigrid is used, with a line smoother able to deal with stretched cells. For flow problems around objects solved with a single block discretization periodic boundary, conditions are prescribed and adaptations for the discretization and the multigrid method are given. Steady flow around a circular cylinder and around an ellipse are presented. © 1994 John Wiley & Sons, Inc.
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  • 19
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 309-322 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We study the Stokes problem by using a mixed finite element method introduced by Stenberg [Numer. Math. 56, 827 (1990)] and adapt it to the splitting introduced by Canuto and Sacchi Landriani [Numer. Math. 50, 217 (1986)] and Chinosi and Comodi [Numer. Methods Partial Different. Equations 7, 363 (1991)], by using the incompressibility condition to implicitly define a boundary condition for the pressure. © 1994 John Wiley & Sons, Inc.
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  • 20
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 323-344 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We analyze a Crank-Nicolson scheme for a family of nonlinear parabolic partial differential equations. These equations cover a wide class of models of excitability, in particular the Hodgkin Huxley equations. To do the analysis, we have in mind the general discretization framework introduced by López-Marcos and Sanz-Serna [in Numerical Treatment of Differential Equations, K. Strehemel, Ed., Teubner-Texte zur Mathematik, Leipzig, 1988, p. 216]. We study consistency, stability and convergence properties of the scheme. We use a technique of modified functions, introduced by Strang [Numer. Math. 6, 37 (1964)], in the study of consistency. Stability is derived by means of the energy method. Finally we obtain existence and convergence of numerical approximations by means of a result due to Stetter (Analysis of Discretization Methods for Ordinary Differential Equations. Springer-Verlag, Berlin, 1973). We show that the method has optimal order of accuracy in the discrete H1 norm. © 1994 John Wiley & Sons, Inc.
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  • 21
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 345-368 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The Jacobi polynomial collocation method is extended to two and three dimensions by superimposing the individual one-dimensional expansions. Two innovative ideas are introduced in this article. The first is the cornerless/edgeless computational grid, and the second is the modified compressibility method, which is an iterative pressure solver. To evaluate the new method's applicability in solving the Navier-Stokes equation, the lid-driven cavity flow problem was solved. Two configurations were considered, the square cavity and the rectangular cavity with an aspect ratio of 2. A comparison of the center-line velocity profiles from two- and three-dimensional simulations at a Reynolds number of 1000 is provided for each of the configurations. The center-line velocity comparisons showed good quantitative agreement with previous studies. © 1994 John Wiley & Sons, Inc.
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  • 22
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 369-381 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Under mild conditions a certain subspace M, consisting of functions which are analytic in a simply connected domain Ω and continuous on the boundary Gamma;, is shown to have real parts which are dense, in the sup norm, in the set of all solutions to the Dirichlet problem for continuous boundary data. Similar results hold for Lp boundary data. Numerical solutions of sample Dirichlet problems are computed. © 1994 John Wiley & Sons, Inc.
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  • 23
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 395-409 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Initial-boundary value problems for nonlinear differential-functional equations are considered. A general class of lines method is investigated. The Perron-type estimation for the right-hand side of the equation with respect to the functional argument is assumed. The proof of the convergence is based on a comparison theorem for differential-difference inequalities. A numerical example is given. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 383-394 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The anomalous infinite propagation speeds in the classical parabolic flow equations are removed by the inclusion of a small amount of fluid elasticity or viscous stress relaxation. The inclusion of such effects results in a hyperbolic system of equations with a complete set of characteristic equations. The directional characteristic equations are used to give insights into the appropriate boundary molecules to be used in finite difference numerical schemes. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994) 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
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    Topics: Mathematics
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  • 26
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    Numerical Methods for Partial Differential Equations 10 (1994), S. i 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
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  • 27
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 475-489 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article we consider upwind finite difference schemes for a class of linear conservation laws with memory. Assuming the positivity of the kernel, it is proved by using the energy estimates that the upwind finite difference scheme, explicit or implicit, is stable and convergent to the real solution. The numerical results of some examples, including Burger's equation with memory, are reported; the effect of memory is also discussed based on the numerical results. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 455-473 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This article addresses and discusses the inaccuracies in finite differencing across the interface of a nested grid. Explicit schemes for the advection and diffusion equations are analyzed on the fine and coarse grids and reformulated at the interface to guarantee that the evolving solution is unaffected by the abrupt change of the spatial grid resolution. The associated errors are expressed as a function of the wavelength of the initial field distribution and the ratio between the coarse and fine grid resolution. It is found that large-scale features of the coarse grid must supply energy to sustain the small-scale features of the fine grid. To not deplete the large-scale motion, a source of energy must be given at the interface in the form of a computational diffusive term with negative viscosity coefficient. On the other hand, not all the energy of the small-scale features of the fine grid has to be transferred to the large-scale motion, but some of it needs to be computationally dissipated at the interface. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 411-434 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: When one uses high-order finite difference schemes for the wave equation, for instance fourth order schemes, the treatment of boundary conditions poses a real difficulty since one needs several additional equations (for the nodes close to the boundary), while one single scalar boundary condition is available. In the case of perfectly reflecting boundary conditions, namely the homogeneous Neumann or Dirichlet conditions, this difficulty can be overcomed by the use of the well-known image principle, which permits the extension of the equation outside of the domain of calculation by an appropriate symmetrization of the data. We propose in this article a generalization of this principle to the absorbing boundary conditions. Through a symmetrization process, we are led to introduce a damped wave equation with a damping term supported by the boundary. The treatment of the boundary condition is then replaced by the approximation of this new damped wave equation in the whole space. The theoretical justification of our approach is based on new energy estimates for the wave equation (when high-order absorbing boundary conditions are used), and constitutes an alternative to the use of the well-known Kreiss criterion to prove the stability of the associated initial boundary value problems. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 435-454 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Numerical methods are proposed for the numerical solution of a system of reaction-diffusion equations, which model chemical wave propagation. The reaction terms in this system of partial differential equations contain nonlinear expressions. Nevertheless, it is seen that the numerical solution is obtained by solving a linear algebraic system at each time step, as opposed to solving a nonlinear algebraic system, which is often required when integrating nonlinear partial differential equations. The development of each numerical method is made in the light of experience gained in solving the system of ordinary differential equations, which model the well-stirred analogue of the chemical system. The first-order numerical methods proposed for the solution of this initialvalue problem are characterized to be implicit. However, in each case it is seen that the numerical solution is obtained explicitly. In a series of numerical experiments, in which the ordinary differential equations are solved first of all, it is seen that the proposed methods have superior stability properties to those of the well-known, first-order, Euler method to which they are compared. Incorporating the proposed methods into the numerical solution of the partial differential equations is seen to lead to two economical and reliable methods, one sequential and one parallel, for solving the travelling-wave problem. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994) 
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    Keywords: Mathematics and Statistics ; Numerical Methods
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 525-532 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The least squares finite element method is a member of the weighted residuals class of numerical methods for solving partial differential equations. The least squares finite element method is applied to the groundwater flow equation. Space is discretized with a C1 continuous trial function and parameters are approximated with a C0 bilinear basis. Solutions for problems containing parameters with large localized spatial gradients are characterized by errors that are propagated throughout the entire domain. Second-order spatial convergence is observed, and extreme mesh refinement is required to match Galerkin and mixed least squares finite element results. Temporal discretization should be kept separate from the least squares spatial discretization. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 491-524 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this study, low and moderate Reynolds number flow problems in the laminar range are solved numerically with grids that do not resolve all the significant scales of motion. Spatial averaging or filtering of the Navier-Stokes equations and Taylor series approximations to the filtered advective terms are used in order to account for the effects of the unresolved or subgrid scales on the resolved scales. Numerical experiments with a transient 2-D lid driven cavity flow problem, using a penalty method Galerkin finite element code, show that this approach enhances the momentum transfer properties of the numerical solution, eliminates 2Δx type oscillations, and enables the use of coarser grids. The significance and order of the terms that describe the interaction between the resolved and the subgrid scales is studied and the success of the series approximations to these terms is demonstrated. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 533-544 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A parallel algorithm for the efficient calculation of m (m ≤ 15) eigenvalues of smallest absolute magnitude for large sparse unsymmetric matrices is implemented and presented. The procedure employes a modification of the reverse simultaneous iteration scheme, which involves, among other things, the solution of m systems of linear equations. This phase is by far the most computationally demanding of the entire algorithm. However, efficient parallelization can be achieved, highly reducing the overall computational load. Numerical experiments consider the calculation of the m = 12 and m = 15 leftmost eigenvalues and eigenvectors of seven test matrices of varying size between n = 512 and n = 3564. All the computations are performed on a 4 CPU CRAY YMP8/432 machine. The accuracy of the eigenpairs found with the proposed algorithm is independent of the number of CPUs employed. Wall clock time and speed-up measurements show that the scheme is efficient and robust and is well parallelized. In fact, average speed-up factors of up to 3.72 were obtained. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. i 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
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    Topics: Mathematics
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 581-585 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new class of finite-difference schemes is constructed for the Fisher partial differential equation. These schemes are constructed according to the nonstandard modeling rules formulated by Mickens. They have the property that, in the appropriate limits, the discrete models obtained are either “exact” or “best” finite-difference schemes for corresponding differential equation. Consequently, the elementary numerical instabilities will not occur. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 545-567 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The utilization and generalization of quadrature and cubature approximations for numerical solution of mathematical models of multivariable transport processes involving integral, differential, and integro-differential operators, and for numerical interpolation and extrapolation, are presented. The methodology for determination of the quadrature and cubature weights for composite operators is developed to accommodate for general functional representations. Application of these methods is demonstrated by solving two-dimensional steady-state and one-dimensional transient-state problems. The solutions are compared with exact-analytical solutions to evaluate the performance of these methods. It is demonstrated that the quadrature and cubature approximations are simple and universal; i.e., the same formula is applicable irrespective of the order of accuracy of the numerical approximation, the type of linear operator, and the number of temporal and/or spatial variables. Since the quadrature and cubature methods can produce solutions with sufficient accuracy even when using fewer discrete points, both the programming task and computational effort are reduced considerably. Therefore, the quadrature and cubature methods appear to be very practical in solving the mathematical models of a variety of transport processes. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 587-590 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 569-580 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A three-dimensional well model (r - θ - z) for the simulation of single-phase fluid flow in porous media is developed. Rather than directly solving the 3-D parabolic PDE (partial differential equation) for fluid flow, the PDE is transformed to a linear operator problem that is defined as u = f(A)σ, where A is a real symmetric square matrix and σ is a vector. The linear operator problem is solved by using the spectral Lanczos decomposition method. This formulation gives continuous solutions in time. A 7-point finite difference scheme is used for the spatial discretization. The model is useful for well testing problems as well as for the simulation of the wireline formation tester tool behavior in heterogeneous reservoirs. The linear operator formulation also permits us to obtain solutions in the Laplace domain, where the wellbore storage and skin can be incorporated analytically. The infinite-conductivity (uniform pressure) wellbore condition is preserved when mixed boundary conditions, such as partial penetration, occur. The numerical solutions are compared with the analytical solutions for fully and partially penetrated wells in a homogeneous reservoir. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 609-623 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The error estimator proposed by Bank and Weiser is analyzed in the case of degree p finite element approximations on quadrilateral meshes. It is shown that the scheme is asymptotically exact in the energy norm for regular solutions provided that the degree of approximation is of odd order and the elements are rectangles. Perhaps surprisingly, the hypotheses are necessary, as counterexamples show. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 591-608 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new mixed finite element for the Stokes equations is considered. This new finite element is based on a mixed formulation of the Stokes problem in which the gradient of the velocity is introduced and the velocity is approximated by the Raviart-Thomas element [1]. Optimal error estimates are derived. The number of degrees of freedom, for this element, is the lowest possible, and the local conservation of the mass is assured. A hybrid version of the mixed method is also considered. Finally, some numerical results for the incompressible Navier-Stokes equations are presented. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 637-650 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Shape optimization of an axisymmetric three-dimensional domain with an elliptic boundary value state problem is solved. Since the cost functional is given in terms of the cogradient of the solution, a dual finite element method based on the minimum of complementary energy principle is used. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 625-635 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article, Zienkiewicz-Zhu estimator is analyzed for the piecewise linear finite element approximate solution of an elliptic problem. The estimator is proved to be equivalent to the error for the Poisson equation with a homogeneous Dirichlet boundary condition for any triangular regular mesh. No assumptions are needed about the regularity of the solution (i.e., solutions with corner singularities are not excluded). The estimator is also proved to be asymptotically exact on subdomains where the solution is smooth when parallel meshes are used. Therefore, its behavior is similar to that of other well-known estimators. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994) 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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    Numerical Methods for Partial Differential Equations 10 (1994), S. i 
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    Keywords: Mathematics and Statistics ; Numerical Methods
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 651-666 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We consider the finite element approximation to the solution of a self-adjoint, second-order elliptic boundary value problem in three dimensions over a fully uniform mesh of piecewise linear tetrahedral elements. Although the resulting approximation to the gradient is optimal for functions from the approximating space, it is, however, only O(h). We show how this can be improved by the recovery, from the finite element solution, of an approximation to the gradient, which is pointwise of a higher order of accuracy than that of the gradient of the finite element approximation. This approximation, termed a recovered gradient function, is, thus, superconvergent. The major task of our analysis is the establishing of an (almost) constant bound on the W11 seminorm of the finite element approximation to a smoothed derivative Green's function. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 667-675 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A new numerical technique for investigating light waves guided by planar nonlinear dielectric films is presented. The method implements a multidomain spectral type approximation based on orthogonal algebraic polynomials, and makes possible to deal with nonperiodic boundary conditions and discontinuities of the data, overcoming the known deficiencies of the trigonometric polynomials. Results of preliminary numerical experiments for the solution of the nonlinear Schrödinger equation are presented. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 689-702 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The nonlinear Poisson-Boltzmann equation is solved in the region between a sphere and a plane, which models the electrolyte solution interface between the tip and the substrate in a scanning tunneling microscope. A finite difference method is used with the domain transformed into bispherical coordinates. Picard iteration with relaxation is used to achieve convergence for this highly nonlinear problem. An adsorbed molecule on the substrate can also be modelled by a superposition of a perturbing potential in a small region of the plane. An approximate analytical solution using a superposition of individual solutions for plane, the adsorbed molecule, and the sphere is also attempted. Results for cases of different potential values on the boundary surfaces and different distances of the sphere from the plane are presented. The results of the numerical method, the approximate analytical method, as well as the previous solutions of the linearized equation are compared. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 677-687 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: von Rosenberg developed an explicit finite-difference scheme for solution of the linear convection-conduction partial differential equation in one space dimension. The method is stable and accurate when a dimensionless ratio of dispersion to convection is between zero and one. In this work, the von Rosenberg method was applied to a linear, one space dimensional set of coupled convection-conduction equations. The system examined involves the change in temperature resulting from a fluid flowing through a stationary porous solid with heat transfer between the fluid and solid phases. The equations, which describe heat transfer in each phase, were solved simultaneously and, thus, the solution method was required to be implicit rather than explicit. It was observed that when the interphase convective heat-transfer rate was small relative to the fluid velocity, an implicit solution of the von Rosenberg weighted equations provided a good solution, but when the interphase convective heat-transfer rate was relatively large, a modified weighting on the equations provided a more accurate, stable solution. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 703-713 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: An Alternating Direction Implicit (ADI), Approximate Factorization (AF) scheme is presented here for the solution of the two-dimensional elliptic partial differential equations, with control functions as source terms, used for grid generation. This scheme requires significantly less computational effort than a Successive Over Relaxation (SOR) scheme. The dependence of the choice of the acceleration parameter on the rate of convergence of the AF scheme has been studied. As an example, grids generated by this method are shown, along with a comparison of the convergence history for the present AF and SOR schemes. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 715-738 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this article we deal with the solution in Ω ⊂ R2 of the quasi linear equation -Δu = f(x, y, u(x, y)) subject to mixed boundary data and representing Gauss' law in a semiconductor device, where u and f are, respectively, the electrostatic potential and the space charge density after a suitable scaling. In the following we consider the associated variational problem of finding in a suitable subspace of H1(Ω) the minimum of the functional \documentclass{article}\pagestyle{empty}\begin{document}$ J(u)\, = \,\int {_\Omega } (\frac{1}{2}\left| {\nabla u\left| {^2 \, - \,{\cal F}(x,y,u)\,d\Omega,} \right.} \right. $\end{document}, where \documentclass{article}\pagestyle{empty}\begin{document}$ {\cal F}(x,y,u)\, = \,\int f (x,y,\xi)\,d\xi, $\end{document} and we prove existence and uniqueness of a weak solution according to the technique of Convex Analysis. The numerical study is then carried on by a piecewise linear finite element approximation, which is proved to converge in the H1-norm to the exact solution of the variational problem; some numerical examples are also included. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 739-755 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Factors influencing the choice of ODE solver for the numerical solution of PDEs by the method of lines are investigated. The advection - diffusion equation is used to gain insight that is generalized to some classes of nonlinear PDEs. Numerical results for several nonlinear PDEs illustrate the theoretical developments. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 757-769 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We prove new pointwise estimates for the time-continuous finite element discretization of a nonlinear Schrödinger equation. The analysis relies on the energy method. A superconvergent estimate of the error gradient is derived and we obtain L∞ estimates via inverse inequalities. We emphasize the case of radial symmetry where the results improve on previously published L2 estimates by allowing greater flexibility in the choice of spatial grid. Some numerical results are presented, which confirm our theoretical findings. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 771-791 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Wave propagation simulation requires a correct implementation of boundary conditions to avoid numerical instabilities. A boundary treatment based on characteristics, which includes as special cases more simple rheologies involving isotropy and elastic behavior, is applied to the anisotropic-viscoelastic wave equation. The method introduces the boundary conditions by specifying the values of the incoming variables, which depend on the solution outside the model volume. The formulation ends up with a wave equation for the boundaries that implicitly includes the boundary conditions. The examples illustrate common problems in geophysical modeling, including free surface and nonreflecting conditions. © 1994 John Wiley & Sons, Inc.
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    Numerical Methods for Partial Differential Equations 10 (1994), S. 793-812 
    ISSN: 0749-159X
    Keywords: Mathematics and Statistics ; Numerical Methods
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We study superconvergence of edge finite element approximations to the magnetostatic problem and to the time-dependent Maxwell system. We show that in special discrete norms there is an increase of one power in the order of convergence of the finite element method compared to error estimates in standard Sobolev norms. Our results are restricted to an orthogonal grid in R3, but the grid may be nonuniform. © 1994 John Wiley & Sons, Inc.
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