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  • 1
    Electronic Resource
    Electronic Resource
    The behaviour of several stress-velocity-pressure mixed finite elements for Newtonian flows (1993)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 17 (1993), S. 99-113 
    Details
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The Q2/P1, P2+/P1, P2/P0 and Q1/P0 velocity-pressure mixed elements are extended to the stress-velocity-pressure formulation, using the same interpolants for stress and velocity, and tested in the 4-to-1 contraction problem for Stokes flow. The comparison shows significant differences among them, which are not present when the velocity-pressure formulation is used.To provide a better understanding of the phenomenon, several variants of the previous elements are introduced, obtained by either changing the pressure space or by enriching the stress space with bubble functions. The formulation exhibits a strong sensitivity to the first alternative, while the second produces only a minor effect. These observations are confirmed by a convergence test effected on a regular problem with the explicit analytical solution. Also, as a result of the whole comparison, the P2+/P2+/P1 element looks promising for three-field calculations.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650170202
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  • 2
    Electronic Resource
    Electronic Resource
    Implementation of the Lagrange-Galerkin method for the incompressible Navier-Stokes equations (1992)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 15 (1992), S. 23-36 
    Details
    ISSN: 0271-2091
    Keywords: Incompressible Navier-Stokes equations ; Finite element method ; Lagrange-Galerkin method ; Geometric search algorithm ; Vortex shedding ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper is concerned with the implementation of Lagrange-Galerkin finite element methods for the Navier-Stokes equations. A scheme is developed to efficiently handle unstructed meshes with local refinement, using a quad-tree-based algorithm for the geometric search. Several difficulties that arise in the construction of the right-hand side are discussed in detail and some useful tricks are proposed.The resulting method is tested on the lid-driven square cavity and the vortex shedding behind a rectangular cylinder and is found to give satisfactory agreement with previous works. A detailed analysis of the effect of time discretization is included.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650150103
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  • 3
    Electronic Resource
    Electronic Resource
    A finite element analysis of rubber coextrusion using a power-law model (1993)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 36 (1993), S. 2143-2156 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A finite element method to simulate coupled thermal viscous coextrusion is presented, with a power-law viscosity function obtained from viscometric data on rubber composites. It combines, by successive substitution iterations, some well-known schemes, such as streamline integration for updating interfaces and Lagrange-Galerkin treatment of the energy equation. Some details of the implementation are discussed. The method is then applied to a comparison of two pre-forming plates for the dual tuber head extruder of Farrel Corporation. Both the normal stress and the temperature at the interface suggest that the presence of a deflector deteriorates the adherence properties. This prediction is in agreement with operational experience.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620361302
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  • 4
    Electronic Resource
    Electronic Resource
    Anisotropic mesh optimization and its application in adaptivity (1997)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 4119-4136 
    Details
    ISSN: 0029-5981
    Keywords: finite elements ; adaptivity ; mesh optimization ; unstructured grids ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The construction of solution-adapted meshes is addressed within an optimization framework. An approximation of the second spatial derivative of the solution is used to get a suitable metric in the computational domain. A mesh quality is proposed and optimized under this metric, accounting for both the shape and the size of the elements. For this purpose, a topological and geometrical mesh improvement method of high generality is introduced. It is shown that the adaptive algorithm that results recovers optimal convergence rates in singular problems, and that it captures boundary and internal layers in convection-dominated problems. Several important implementation issues are discussed. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical study of pyrazole elimination of N-alkyl pyrazoles (1989)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 225-231 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The gas-phase pyrazole elimination of N-alkyl pyrazoles has been studied using MNDO semi-empirical molecular orbital (MO) theory with complete geometry optimization of all stationary points. We found that the activation energies (Ea) of the concerted processes are around 80 kcal/mol, 25 Kcal/mol higher than experimental values. But the differences in Ea between compounds with different substituents are in good agreement with the experimental ones.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610020305
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical study of the gas-phase thermal isomerization of isoxazoles. Part I. Isoxazole (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 611-619 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An MNDO study was made of the gas-phase thermal isomerization of isoxazole to explore theoretically the proposed reaction mechanism. The results showed that isoxazole isomerizes through an azirine, as an intermediate, to oxazole via a nitrile ylide or to ketenimine, with similar activation energies, and that the first step is rate limiting, in agreement with the experimental results. These results also show that isomerization to a nitrile is possible, but in this case the energy barrier is grater than the corresponding isomerization to oxazole. The MNDO study also supports a concerted process for the rate-limiting step, as reported earlier on the basis of experimental studies.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030910
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  • 7
    Electronic Resource
    Electronic Resource
    Evaluation of solvent effects on the dissociation of aliphatic carboxylic acids in aqueous N,N-dimethylformamide mixtures according to the scaled particle theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 87-95 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The standard Gibbs energies of transfer, ΔGt° from water to water-N,N-dimethylformamide mixtures for the dissociation process of several organic acids (formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids) obtained from the pKa* values are discussed in terms of the extended Scaled Particle Theory from quantum mechanical calculations in order to estimate the cavity and electrostatic contributions. The residual energy term was correlated with the hydrogen bond acceptor density and the Kamlet-Taft β parameters. The main contribution to ΔGt° was due to dipolar and specific interactions.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040204
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  • 8
    Electronic Resource
    Electronic Resource
    A direct solver for the least-squares problem arising from GMRES(k) (1994)
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 10 (1994), S. 743-749 
    Details
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This is a study about one of the core questions in the GMRES(k) method regarding the obtaining of vector yk for the least-squares problem, argminy |Hky - β(n)e1|2 (see Saad and Schultz1). We propose a simple but efficient approach to the resolution of this problem and a low cost computation of the residual and the residual norm, including both in a complete and detailed FGMRES(k) algorithm. The whole algorithm of minimization only involves two backward substitutions with triangular matrices and a dot product. The residual and the residual norm are computed, making use of results in the least-squares problem.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cnm.1640100909
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  • 9
    Electronic Resource
    Electronic Resource
    Biquaternionic Integral Representations for Massive Dirac Spinors in a Magnetic Field and Generalized Biquaternionic Differentiability (1996)
    Chichester, West Sussex : Wiley-Blackwell
    Mathematical Methods in the Applied Sciences 19 (1996), S. 1415-1431 
    Details
    ISSN: 0170-4214
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The Dirac equation with a vector potential is considered using a biquaternionic formalism and boundary integral representations for its solutions are obtained. In order to characterize these solutions by a property of local approximability by linearization the corresponding notion of biquaternionic differentiability and its generalization in the sense of Bers (adapted to the spatial case) are given.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Scattering Frequencies and a Class of Perturbed Systems of Elastic Waves (1996)
    Chichester, West Sussex : Wiley-Blackwell
    Mathematical Methods in the Applied Sciences 19 (1996), S. 699-716 
    Details
    ISSN: 0170-4214
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We consider the system of elastic waves in three dimensions under the presence of an impurity of the medium which we represent by a real-valued function q(x) (or q(x,t)). The medium is assumed to be isotropic and occupies the whole space Ω = ∝3. We study the location of the scattering frequencies associated with such phenomenon. We conclude that there is a large region on the complex plane which is free of scattering frequencies. In the remaining region they are discrete provided that q satisfies suitable assumptions concerning its behaviour at infinity.
    Type of Medium: Electronic Resource
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