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  • Engineering  (447)
  • Inorganic Chemistry
  • 1995-1999  (294)
  • 1990-1994  (455)
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  • 1930-1934  (69)
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  • 11
    Electronic Resource
    Electronic Resource
    AN ADAPTIVE AGGLOMERATION METHOD FOR ADDITIVE CORRECTION MULTIGRID (1997)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 887-903 
    Details
    ISSN: 0029-5981
    Keywords: multigrid ; adaptive agglomeration ; additive correction ; anisotropic grids ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the computational simulation of fluid flow and scalar transport, multigrid iterative solution techniques often fail or stall when the discrete linearized equations have strongly anisotropic coefficients. In the present work, an adaptive agglomeration algorithm for forming coarse grids is presented that allows multigrid techniques to work efficiently for equation sets with anisotropic coefficients. The adaptive agglomeration is defined by two rules and several guidelines that follow from a physical interpretation of the performance of iterative solvers like Gauss-Seidel. The effectiveness of the adaptive agglomeration algorithm is demonstrated for a wide range of test cases. © 1997 by John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Large deflection elastic-plastic analysis of cylindrical shells using the finite strip method (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 31 (1991), S. 837-857 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The finite strip method is extended to the non-linear, static analysis of cylindrical shells. Large deflection effects are incorporated via first-order non-linearities in the strain-displacement relations, and material non-linearities are included via the von Mises yield criteria and associated flow rule. Numerical results are presented for various example problems including the diaphragm supported cylindrical shell-roof problem, an axisymmetric cylindrical shell loaded by radial pressure, the cylindrical shell-roof problem with clamped curved ends and a pressure loaded cylindrical panel clamped all round. The results are compared with known results from analytical and/or finite element analyses. The results indicate that a single bending mode in the strip direction is sufficient in most cases to yield engineering accuracy for preliminary design purposes.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620310503
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  • 13
    Electronic Resource
    Electronic Resource
    CONSISTENT LINEARIZATION FOR THE EXACT STRESS UPDATE OF PRANDTL-REUSS NON-HARDENING ELASTOPLASTIC MODELS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1219-1235 
    Details
    ISSN: 0029-5981
    Keywords: plasticity ; numerical integration algorithms ; consistent linearization ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a consistent algorithm, which combines the advantages of the exact time integration of Prandtl-Reuss elastoplastic models and the quadratic asymptotic convergence of Newton-Raphson iteration strategies. The consistent modulus is evaluated by a full linearization of the exact stress update procedure. Numerical tests for a thin wall tube subjected to combined loads of tension and torsion are performed to illustrate the accuracy and efficiency of the consistently linearized exact stress update algorithm described in the paper. For comparison purpose numerical results of the radial return method are also given.
    Additional Material: 6 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    COMPARATIVE EVALUATION OF DIFFERENT OPTIMIZATION ALGORITHMS FOR STRUCTURAL DESIGN APPLICATIONS (1996)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 1761-1774 
    Details
    ISSN: 0029-5981
    Keywords: optimization ; algorithms ; structural ; design ; comparative ; evaluation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Non-linear programming algorithms play an important role in structural design optimization. Fortunately, several algorithms with computer codes are available. At NASA Lewis Research Centre, a project was initiated to assess the performance of eight different optimizers through the development of a computer code CometBoards. This paper summarizes the conclusions of that research. CometBoards was employed to solve sets of small, medium and large structural problems, using the eight different optimizers on a Cray-YMP8E/8128 computer. The reliability and efficiency of the optimizers were determined from the performance of these problems. For small problems, the performance of most of the optimizers could be considered adequate. For large problems, however, three optimizers (two sequential quadratic programming routines, DNCONG of IMSL and SQP of IDESIGN, along with Sequential Unconstrained Minimizations Technique SUMT) outperformed others. At optimum, most optimizers captured an identical number of active displacement and frequency constraints but the number of active stress constraints differed among the optimizers. This discrepancy can be attributed to singularity conditions in the optimization and the alleviation of this discrepancy can improve the efficiency of optimizers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Some computational issues in strain localization problems for rate independent solids (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 32 (1991), S. 79-101 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Issues related to the constitutive modelling and computational treatment of strain localization are examined for the class of rate independent solids. The significance of the constitutive description in localization problems is emphasized and constitutive models currently employed are briefly reviewed. Difficulties faced in finite element analysis, fundamentally associated with the loss of ellipticity of the related boundary value problem, and present trends in the computational treatment are discussed and illustrated by numerical examples.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620320106
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  • 16
    Electronic Resource
    Electronic Resource
    A multi-grid enhanced GMRES algorithm for elasto-plastic problems (1998)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 1441-1462 
    Details
    ISSN: 0029-5981
    Keywords: GMRES ; Galerkin multi-grid ; variable preconditioning scheme ; conjugate gradient method ; large-scale elasto-plastic problem ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A combination of both GMRES and multi-grid (MG) methods is presented in this paper for solving large-scale two- and three-dimensional elasto-plastic problems, in which each MG iteration cycle serves as the preconditioning step for the GMRES procedure. A particular multi-grid approach, termed the Galerkin multi-grid scheme, is considered and the main effort is devoted to the implementation aspects of the proposed algorithm. Numerical examples, characterised by large-scale (up to 82145 DOF), strong non-linearity (nearly plastic limit state, necking and localization) and severe ill-conditioned states (presence of loading limit points), and also involving symmetric and unsymmetric as well as SPD and indefinite system matrices, are provided. The numerical results illustrate that the proposed method exhibits a remarkable performance in terms of efficiency and robustness in all circumstances. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    The boundary element solution of the Laplace and biharmonic equations subjected to noisy boundary data (1998)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 479-492 
    Details
    ISSN: 0029-5981
    Keywords: boundary element method (BEM) ; singular value decomposition (SVD) ; L-curve method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This study investigates the numerical solution of the Laplace and biharmonic equations subjected to noisy boundary data. Since both equations are linear, they are numerically discretized using the Boundary Element Method (BEM), which does not use any solution domain discretization, to reduce the problem to solving a system of linear algebraic equations for the unspecified boundary values. It is shown that when noisy, lower-order derivatives are prescribed on the boundary, then a direct approach, e.g. Gaussian elimination, for solving the resulting discretized system of linear equations produces an unstable, i.e. unbounded and highly oscillatory, numerical solution for the unspecified higher-order boundary derivatives data. In order to overcome this difficulty, and produce a stable solution of the resulting system of linear equations, the singular value decomposition approach (SVD), truncated at an optimal level given by the L-curve method, is employed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Der Gaskomplex MnAlF5 und sein Einfluß auf die sublimative Reinigung von AlF3Professor Heinrich Oppermann zum 60. Geburtstag gewidmet (1994)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 620 (1994), S. 1976-1982 
    Details
    ISSN: 0044-2313
    Keywords: Gas complex ; MnAlF5 ; mass spectroscopy ; enthalpie of dissociation ; ab initio calculation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The Gas Complex MnAlF5 and its Influence on the Purification of AlF3 by SublimationThe gas complex MnAlF5 has been determined mass spectroscopically by the ions MnAlF5+ and MnAlF4+. The gas complex MnAlF5 is formed above 973 K by heating up mixtures of AlF3/MnF2 or AlF3 · 3 H2O endowed with Mn2+ or by heating up solid MnAlF5 too. At 1 008 K the enthalpie of dissociation is 197 kJ/mole. The equilibrium structures of the high spin molecule MnAlF5 (S = 5/2) were examined with ab initio calculations at the HF-level by comlete gradient optimizing. Two minimum structures were found on the potential energy surface. A bidentate fluorine bridged structure was found to be the most stable at the HF-level. Vibrational frequencies and thermodynamic functions of complex formation were estimated for both minimum structures. The importance of the formation of the gas complex for the separation of MnF2 and AlF3 by sublimation is discussed.
    Notes: Der Gaskomplex MnAlF5 wurde bei massenspektrometrischen Untersuchungen durch die Ionen MnAlF5+ und MnAlF4+ nachgewiesen; er bildet sich beim Aufheizen von AlF3/MnF2-Gemengen, Mn-dotiertem AlF3 · 3 H2O bzw. festem MnAlF5 oberhalb 973 K. Die experimentell ermittelte Dissoziationsenthalpie bei 1 008 K für den Zerfall MnAlF5(g) = MnF2(g) + AlF3(g) beträgt 197 kJ/mol. Die Gleichgewichtsstrukturen von MnAlF5(g) (high spin; S = 5/2) wurden durch ab initio Berechnungen auf HF-Niveau durch vollständige Gradientenoptimierung ermittelt. Zwei Minimumstrukturen wurden gefunden. Eine zweifach F-verbrückte Ringstruktur ist auf HF-Niveau die stabilste. Schwingungsfrequenzen und thermodynamische Komplexbildungsfunktionen werden für beide Minimumstrukturen angegeben. Die Bedeutung des Gaskomplexes für die sublimative Trennung von MnF2 und AlF3 wird diskutiert.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19946201123
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  • 19
    Electronic Resource
    Electronic Resource
    Synthese und Strukturbestimmung von (tBuP)4Sn(CH3)2 und (CH3)2Sn[(tBu)P—P(tBu)]2Sn(CH3)2 (1995)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 621 (1995), S. 1358-1364 
    Details
    ISSN: 0044-2313
    Keywords: Phosphorus tin heterocycles ; syntheses ; crystal structure ; NMR ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis and Structure Analysis of (tBuP)4Sn(CH3)2 and (CH3)2Sn[(tBu)P—P(tBu)]2Sn(CH3)2The diphosphides K2[(tBu)P—(tBuP)2—P(tBu)] 7 or K2[(tBu)P—P(tBu)] 8 react with (CH3)2SnCl2 in a molar ratio of 1 : 1 to form the binary 5-membered ring system P4Sn 4 a and the 6-membered ring system Sn(P2)2Sn 5 a respectively. When (CH3)2SnCl2, however, is treated with 8 in a molar ratio of 2 : 1 the 4-membered ring system P3Sn 2 a is formed which includes the fragmentation of the intermediate K2[(CH3)2Sn ((tBu)P—P(tBu))2] 9. 4 a and 5 a could be obtained in a pure form and characterized NMR spectroscopically and by X-ray structure analyses; 2 a was identified only NMR spectroscopically.
    Notes: Die Diphosphide K2[(tBu)P—(tBuP)2—P(tBu)] 7 bzw. K2[(tBu)P—P(tBu)] 8 reagieren mit (CH3)2SnCl2 im Molverhältnis 1 : 1 zu dem binären Fünfringsystem P4Sn 4 a bzw. dem Sechsringsystem Sn(P2)2Sn 5 a. Wird jedoch (CH3)2SnCl2 mit zwei Äquivalenten 8 umgesetzt, so erhält man nach einer Fragmentierung des Intermediats K2[(CH3)2Sn ((tBu)P—P(tBu))2] 9 das binäre Vierringsystem P3Sn 2 a. 4 a und 5 a konnten in reiner Form isoliert, NMR-spektroskopisch und durch Röntgenstrukturanalysen charakterisiert werden; 2 a konnte bisher nur NMR-spektroskopisch identifiziert werden.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19956210814
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  • 20
    Electronic Resource
    Electronic Resource
    Synthese und Struktur von Hexa-t-butyl-1,4-dichloro-1,4-distanna-2,3,5,6,7,8-hexaphosphabicyclo[2.2.2]octan - Eine neue Käfigverbindung mit dem Sn(P2)3Sn-Gerüst (1996)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 622 (1996), S. 1793-1798 
    Details
    ISSN: 0044-2313
    Keywords: Sn(P2)3Sn cage system ; NMR data, crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis and Structure of Hexa-t-butyl-1,4-dichloro-1,4-distanna-2,3,5,6,7,8-hexaphosphabicyclo[2.2.2]octane - a New Cage Compound with the Sn(P2)3Sn SkeletonThe reaction of the diphosphide K2[(tBuP)2] 1 with SnCl4 leads by a redox process mainly to (tBuP)3,4 and other sideproducts. However, at the same time a threefold [2 + 1]-cyclocondensation reaction takes place yielding the new cage compound hexa-t-butyl-1,4-dichloro-1,4-distanna-2,3,5,6,7,8-hexaphosphabicyclo[2.2.2]octane, ClSn(tBuP—PtBu)3SnCl 2. 2 could be obtained in a pure form and characterized 31P and 119Sn NMR spectroscopically; 2 was also characterized by a single crystal structure analysis.
    Notes: Bei der Reaktion zwischen dem Diphosphid K2[(tBuP)2] 1 und SnCl4 finden überwiegend Redoxreaktionen statt, die zu (tBuP)3,4 und weiteren Nebenprodukten führen. Gleichzeitig findet aber auch eine dreifache [2 + 1]-Cyclokondensation statt, bei der die neuartige Käfigverbindung Hexa-t-butyl-1,4-dichloro-1,4-distanna-2,3,5,6,7,8-hexaphospha-bicyclo[2.2.2]octan, ClSn(tBuP—PtBu)3SnCl 2 gebildet wird. 2 konnte in reiner Form isoliert und 31P- und 119Sn-NMR-spektroskopisch sowie durch eine Einkristallstrukturanalyse charakterisiert werden.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19966221026
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