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  • 1
    Electronic Resource
    Electronic Resource
    Two stable POD-based approximations to the Navier–Stokes equations (2000)
    Springer
    Computing and visualization in science 3 (2000), S. 61-66 
    Details
    ISSN: 1433-0369
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract. The governing equations of viscous flows, the Navier–Stokes equations, are approximated by means of a low order model based on proper orthogonal decomposition (POD). Numerical evidence and analysis of simplified models show that the resulting time-wise semidiscretization is only marginally stable. Here, two methods providing additional stabilization are described: the first is based on a Lax–Wendroff type artificial diffusion term, while the second is a reinterpretation of POD in the frame of the finite element functional least square method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007910050052
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  • 2
    Electronic Resource
    Electronic Resource
    An Additive Multilevel Optimization Method and Its Application to Unstructured Meshes (1997)
    Springer
    Journal of scientific computing 12 (1997), S. 233-251 
    Details
    ISSN: 1573-7691
    Keywords: Optimization ; multilevel method ; unstructured meshes ; agglomeration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper describes a new approach of the Multilevel optimization method (MLO) studied in Refs. 4 and 11. The previous approach of the multilevel method was a multiplicative or serial method since each level is addressed sequentially; it presents, as MG methods, a mesh-independent convergence rate. It is more costly than MG methods, but easier to implement. In order to smooth all the frequency components of the error, the V-cycle strategy is used and it results in several cost functional evaluations per cycle. The proposed new strategy is based on an additive approach. A new preconditioner is deduced from this multilevel method, which provides a better efficiency than the previous method since all frequencies are addressed in only one optimization iteration. An abstract analysis seems to indicate a mesh independent convergence rate. All application to unstructured meshes is derived by combining with a volume agglomeration approach and illustrates the behavior predicted by the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1025697310775
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  • 3
    Electronic Resource
    Electronic Resource
    Feeding ecology and life history variation of the blue tit in Mediterranean deciduous and sclerophyllous habitats (1991)
    Springer
    Oecologia 88 (1991), S. 9-14 
    Details
    ISSN: 1432-1939
    Keywords: Blue tit ; Diet ; Feeding frequency ; Breeding traits ; Evergreen habit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary High variation in laying date and clutch size of the blue tit between a Mediterranean mixed habitat on the mainland, southern France, and a sclerophyllous habitat on the island of Corsica is hypothesized to be related to differences in the food supply. The diet of the nestlings and feeding frequencies were studied using camera nestboxes and electronic chronographs. Food items brought to the nestlings were much more diverse on Corsica than on the mainland, including many fewer caterpillars and a wider range of taxa. However, when expressed as a volume index, prey items were on average larger on Corsica than on the mainland. Feeding frequencies were significantly lower on Corsica. A good correlation was found in both habitats between laying date and the caterpillar peak date, although both the leafing development of oaks and the peak of abundance of caterpillars occurred 3 weeks later in the Corsican sclerophyllous trees than in the mainland deciduous ones. Differences in the feeding ecology of tits between the two habitats are discussed in the light of the evergreen habit, which means that only 30% of leaves are available for phyllophagous insects instead of 100% in deciduous trees. the combination of a late and low food supply in evergreen trees is the best explanation for the differences in breeding traits betwen the two populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328397
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  • 4
    Electronic Resource
    Electronic Resource
    Relationship between temperature and the timing of breeding of the Blue Tit (Parus caeruleus) in two Mediterranean oakwoods (1991)
    Springer
    Journal of ornithology 132 (1991), S. 297-301 
    Details
    ISSN: 1439-0361
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Die zahlreich publizierten Korrelationen zwischen Wärmesummen und Beginn der jährlichen Legeperiode bei Meisen (Paridae), bilden keinen Beweis für einen direkten Einfluß der Temperatur auf den Legebeginn. Solche Korrelationnen beruhen außerdem auf statistische fraglichen Auswertungen. Untersuchungen an einer Blaumeisenpopulation (Parus caeruleus) in zwei benachbarten, aber verschiedenen Bruthabitaten im mediterranen Südfrankreich zeigten, daß höchstens ein längerer Zeitabschnitt (1. Januar bis 10. April) mit physiologischer Bedeutung in Betracht zu ziehen ist. Je höher die Durchschnittstemperatur in dieser Periode, um so früher der Legebeginn, der jedoch hauptsächlich durch die zeitlich unterschiedlichen Nahrungsangebote in den beiden untersuchten Habitaten erklärt wird.
    Notes: Summary Correlations between warmth sum and egg laying in tits (Paridae) were often found but do not prove that there is a direct influence of temperature on egg laying date. Such correlations are also open to criticism because they involve a statistical bias (i. e. the selection of variables). Studies of a Blue Tit population in two close but different habitats in Mediterranean France showed that it is better, at least, to consider a time period with a physiological signification (1 January–10 April). We found that the higher the mean temperature in this time period, the earlier the egg laying commenced. Egg laying dates of the Blue Tit in the two habitats are primarily attributed to habitat-related feeding resources.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01640538
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  • 5
    Electronic Resource
    Electronic Resource
    A perturbation study of the obstacle problem by means of a generalized implicit function theorem (1981)
    Springer
    Annali di matematica pura ed applicata 127 (1981), S. 321-364 
    Details
    ISSN: 1618-1891
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary The Nash-Moser Implicit Function Theorem is applied to the study of the perturbation of the geometrical domain of an Obstacle Problem, considered as a Free Boundary Problem in an annular region of the plane. Applications to Optimal Control are derived and numerical results are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01811729
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  • 6
    Electronic Resource
    Electronic Resource
    Unstructured volume-agglomeration MG: Solution of the Poisson equation (1994)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 18 (1994), S. 27-42 
    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: We are interested in solving second-order PDEs with multigrid and unstructured meshes. The multigrid strategy we present here is adapted from the generalized finite volume agglomeration multigrid algorithm we have developed recently for the solution of the Euler equations. We now focus on Poisson's equation. A strategy is defined by introducing a correction factor for the diffusive terms, and some illustrating results are given.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650180103
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  • 7
    Electronic Resource
    Electronic Resource
    Some explicit triangular finite element schemes for the Euler equations (1984)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 4 (1984), S. 749-764 
    Details
    ISSN: 0271-2091
    Keywords: Hyperbolic Conservation Equation ; Finite Elements ; 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: Several explicit schemes are presented for triangular P0 and P1 finite elements. A first-order accurate upwind P0 scheme is compared to a FLIC type method. A second-order accurate Richtmyer scheme is constructed. Applications are given for the Euler system of conservation laws in the 2-dimensional case.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650040804
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  • 8
    Electronic Resource
    Electronic Resource
    A semi-coarsening strategy for unstructured multigrid based on agglomeration (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 927-957 
    Details
    ISSN: 0271-2091
    Keywords: multigrid methods ; finite elements ; finite volumes ; semi-coarsening ; numerical analysis ; turbulent flows ; compressible flows ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Extending multigrid concepts to the calculation of complex compressible flow is usually not straightforward. This is especially true when non-embedded grid hierarchies or volume agglomeration strategies are used to construct a gradation of unstructured grids. In this work, a multigrid method for solving second-order PDE's on stretched unstructured triangulations is studied. The finite volume agglomeration multigrid technique originally developed for solving the Euler equations is used (M.-H. Lallemand and A. Dervieux, in Multigrid Methods, Theory, Applications and Supercomputing, Marcel Dekker, 337-363 (1988)). First, a directional semi-coarsening strategy based on Poisson's equation is proposed. The second-order derivatives are approximated on each level by introducing a correction factor adapted to the semi-coarsening strategy. Then, this method is applied to solve the Poisson equation. It is extended to the 2D Reynolds-averaged Navier-Stokes equations with appropriate boundary treatment for low-Reynolds number turbulent flows. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 32 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 9
    Electronic Resource
    Electronic Resource
    Computation of unsteady flows with mixed finite volume/finite element upwind methods (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 193-206 
    Details
    ISSN: 0271-2091
    Keywords: finite element ; finite volume ; numerical dissipation ; compressible flow ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We refer to as mixed element/volume (MEV) methods the application of finite element for diffusion terms and finite volume for advection terms in a flow model. The compatibility of these methods can be checked for some low-order approximations; the resulting schemes may enjoy the relative mesh-regularity-independent accuracy of finite element methods as discussed in a first section. In recent years a number of developments (by INRIA Dassault and T. Barth, among others) have produced P1-continuous schemes that involve some MUSCL/TVD unidirectional limitation; the resulting schemes are very useful but sometimes may involve much more numerical viscosity than necessary, especially for unsteady computations. In the present study, a new version is built by using a larger molecule for the intercell flux evaluation. The 1D version can be promoted to fourth- or even fifth-order spatial accuracy. The 2D version is no better than second-order-accurate; however, it involves only a sixth-order dissipation and the global accuracy is markedly improved even on irregular meshes. The above development extends the ability of the MUSCL/MEV scheme towards the accurate calculation of unsteady flows involving vortex shedding. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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