1,721,043 research outputs found
ADIGMA-A European Project on the Development of Adaptive Higher-Order Variational Methods for Aerospace Applications
No full textADIGMA - A European Project on the Development of Adaptive Higher-Order Variational Methods for Aerospace Application
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multidimensional upwind residual distribution schemes for the Euler and Navier-Stokes equations on unstructured grids
No full text<p align="justify">Une approche multidimensionelle pour la résolution numérique des équations d'Euler et de Navier-Stokes sur maillages non-structurés est proposée. Dans une première partie, un exposé complet des schémas de distribution, dits de "fluctuation-splitting" ,est décrit, comprenant une étude comparative des schémas décentrés, positifs et de 2ème ordre, pour résoudre l'équation de convection à coefficients constants, ainsi qu'une étude théorique et numérique de la précision des schémas sur maillages réguliers et distordus. L'extension à des lois de conservation non-linéaires est aussi abordée, et une attention particulière est portée au problème de la linéarisation conservative. Dans une deuxième partie, diverses discrétisations des termes visqueux pour l'équation de convection-diffusion sont développées, avec pour but de déterminer l'approche qui offre le meilleur compromis entre précision et coût. L'extension de la méthode aux systèmes des lois de conservation, et en particulier à celui des équations d'Euler de la dynamique des gaz, représente le noyau principal de la thèse, et est abordée dans la troisième partie. Contrairement aux schémas de distribution classiques, qui reposent sur une extension formelle du cas scalaire, l'approche développée ici repose sur une décomposition du résidu par élément en équations scalaires, modélisant le transport de variables caracteristiques. La difficulté vient du fait que les équations d'Euler instationnaires ne se diagonalisent pas, et admettent une infinité de solutions élémentaires (ondes simples) se propageant dans toutes les directions d'espace. En régime stationnaire, en revanche, les équations se diagonalisent complètement dans le cas des écoulements supersoniques, et partiellement dans le cas des écoulements subsoniques. Ainsi, les équations sous forme conservative peuvent être remplacées par un système équivalent comprenant deux équations totalement découplées, exprimant l'invariance de l'entropie et de l'enthalpie totale le long des lignes de courant, et deux autres équations, modélisant les effets purement acoustiques. En régime supersonique, celles-ci se découplent aussi, et expriment la convection le long des lignes de Mach d'invariants de Riemann généralisés. La discrétisation de ces équations par des schémas scalaires décentrés permet de simuler des écoulements continus et discontinus avec une grande précision et sans oscillations. Finalement, dans une dernière partie, l'extension aux équations de Navier-Stokes est abordée, et la discrétisation des termes visqueux par une approche éléments finis est proposée. Les résultats numériques confirment la précision et la robustesse de la méthode.</p>Doctorat en sciences appliquéesinfo:eu-repo/semantics/nonPublishe
Adaptive unstructured mesh algorithms and SUPG finite element method for compressible high reynolds number flows
No full textDoctorat en sciences appliquéesinfo:eu-repo/semantics/nonPublishe
Numerical Analysis of Higher Order Discontinuous Galerkin Finite Element Methods
No full textAfter the introduction in Section 1 this lecture starts off with
recalling well-known results from the numerical analysis of the
continuous finite element methods. In particular, we recall a
priori error estimates in the energy norm and the
L2-norm including their proofs for higher order standard
finite element methods of Poisson's equation in Section 2 and for the
standard and the streamline diffusion finite element method of the
linear advection equation in Section 3.
We then introduce the discontinuous Galerkin discretization of the
linear advection equation in Section 4. Following
[Brezzi-Marini-Süli-2004] we consider two numerical flux
functions, the mean-value flux and the upwind flux, and derive the
corresponding a priori error estimates. Whereas the standard
Galerkin discretization of the linear advection equation is unstable
and requires e.g. streamline diffusion for stabilization, we will see
in Section 4 that the discontinuous Galerkin discretization of the
linear advection based on upwind is stable without addition of
streamline diffusion.
Then in Section 5, we follow [Arnold-Brezzi-Cockburn-Marini-2002] and
derive and analyze a variety of discontinuous Galerkin discretizations
of Poisson's equations. In particular, we derive the symmetric and
non-symmetric interior penalty Galerkin method (SIPG and NIPG), the
method of Baumann-Oden (BO) and the first and second method of Bassi
and Rebay (BR1 and BR2). The analysis of the methods includes the
consistency and adjoint consistency of the schemes, continuity and
coercivity of the respective bilinear forms and a priori
error estimates for the interior penalty methods. In particular, we
will see that the adjoint consistent SIPG scheme is of optimal order
in the L2-norm whereas the adjoint inconsistent NIPG scheme
is not.
Motivated by the connection of adjoint consistency of DG
discretizations to the availability of optimal order error estimates
in the L2-norm we concentrate on the adjoint consistency
property in Section 6. In particular, here we follow [Hartmann-2007]
and give a general framework for analyzing the consistency and adjoint
consistency of DG discretizations for linear problems with
inhomogeneous boundary conditions. This includes the derivation of
continuous adjoint problems associated to specific target quantities,
the derivation of primal and adjoint residual forms of the
discretizations and the discussion whether the discretizations in
combination with specific target quantities J(.) are adjoint
consistent or not. This analysis is performed in Sections 6.3 and 6.4
for the interior penalty DG discretization of the Dirichlet-Neumann
boundary value problem of Poisson's equations and for the upwind DG
discretization of the linear advection equation, respectively.
Then in Section 7 the previously shown properties and estimates for
the interior penalty and the upwind DG discretization are used to
derive a priori estimates for the error measured in terms of
target quantities J(.). Here again, we will see that a discretization
must be consistent and adjoint consistent in order to provide optimal
error estimates in J(.).
This lecture is finalized with the Sections 8 and 9 which introduce
the DG discretizations of the compressible Euler and Navier-Stokes
equations. Additionally, the consistency and adjoint consistency
analysis which has been introduced in Section 6 for linear problems is
now generalized to nonlinear problems in Section 8.5. This analysis is
performed for the compressible Euler and Navier-Stokes equations in
Sections 8.6 and 9.3, respectively. This includes the derivation of an
adjoint consistent discretization of boundary conditions and of target
functionals. Here particular emphasis is placed on the aerodynamic
force coefficients like the drag, lift and moment coefficients.
Various examples in Sections 5.6, 7.3, 8.7 and 9.4 illustrate the
numerical methods described.
In particular, the contents of this lecture is given as follows
1) Introduction
1.1) Higher order discretization methods
1.2) Discontinuous Galerkin discretizations
1.3) Numerical analysis of finite element methods
1.4) Outline
2) Higher order continuous FE methods for Poisson's equation
2.1) Poisson's equation
2.1.1) The homogeneous Dirichlet problem
2.1.2) The inhomogeneous Dirichlet problem
2.1.3) The Neumann problem
2.2) The standard finite element method for Poisson's equation
2.2.1) Consistency
2.2.2) Existence and uniqueness of discrete solutions
2.2.3) Best approximation property
2.2.4) Interpolation estimates
2.2.5) A priori error estimates in the H1- and L2-norm
3) Higher order continuous FE methods for the linear advection equation
3.1) The linear advection equation
3.1.1) Variational formulation with strong boundary conditions
3.1.2) Variational formulation with weak boundary conditions
3.2) The standard Galerkin method with weak boundary conditions
3.3) The streamline diffusion method with weak boundary conditions
4) Higher order DG discretizations of the linear advection equation
4.1) Mesh related function spaces
4.2) A variational formulation of the linear advection equation
4.3) Consistency, conservation property, coercivity and stability
4.4) The discontinuous Galerkin discretization
4.5) The local L2-projection and approximation estimates
4.6) A priori error estimates
4.7) The discontinuous Galerkin discretization based on upwind
4.7.1) The importance of the inter-element jump terms
4.7.2) The global and local conservation property
4.7.3) Consistency
5) Higher order DG discretizations of Poisson's equation
5.1) The system and primal flux formulation
5.2) The DG discretization: Consistency and adjoint consistency
5.3) Derivation of various DG discretization methods
5.3.1) The SIPG and NIPG methods and the method of Baumann-Oden
5.3.2) The original DG discretization of Bassi and Rebay (BR1)
5.3.3) The modified DG discretization of Bassi and Rebay (BR2)
5.4) Consistency, adjoint consistency, continuity and coercivity
5.5) A priori error estimates
5.6) Numerical results
6) Consistency and adjoint consistency for linear problems
6.1) Definition of consistency and adjoint consistency
6.2) The consistency and adjoint consistency analysis
6.3) Adjoint consistency analysis of the IP discretization
6.3.1) The continuous adjoint problem to Poisson's equation
6.3.2) Primal residual form of the interior penalty DG discretization
6.3.3) Adjoint residual form of the interior penalty DG discretization
6.4) Adjoint consistency analysis of the upwind DG discretization
6.4.1) The continuous adjoint problem to the linear advection equation
6.4.2) Primal residual form of the DG discretization based on upwind
6.4.3) Adjoint residual form of the DG discretization based on upwind
7) A priori error estimates for target functionals J(.)
7.1) Upwind DG of the linear advection equation: Estimates in J(.)
7.2) IP DG discretization for Poisson's equation: Estimates in J(.)
7.3) Numerical results
8) Discontinuous Galerkin discretizations of the compressible Euler equations
8.1) Hyperbolic conservation equations
8.2) The compressible Euler equations
8.3) The DG discretization of the compressible Euler equations
8.4) Boundary conditions
8.5) Consistency and adjoint consistency for nonlinear problems
8.5.1) The consistency and adjoint consistency analysis
8.6) Adjoint consistency analysis of DG for the compressible Euler equations
8.6.1) The continuous adjoint problem to the compressible Euler equations
8.6.2) Primal residual form of DG for the compressible Euler equations
8.6.3) Adjoint residual form of DG for the compressible Euler equations
8.7) Numerical results
9) DG discretizations of the compressible Navier-Stokes equations
9.1) The compressible Navier-Stokes equations
9.2) DG discretizations of the compressible Navier-Stokes equations
9.3) Adjoint consistency analysis of DG for the compressible Navier-Stokes equations
9.3.1) The continuous adjoint problem to the compressible NS equations
9.3.2) Primal residual form of DG for the compressible NS equations
9.3.3) Adjoint residual form of DG for the compressible NS equations
9.4) Numerical results
Acknowledgements
Bibliograph
Error estimation and adaptive mesh refinement for aerodynamic flows
Get PDFThis lecture course covers the theory of so-called duality-based a
posteriori error estimation of DG finite element methods. In
particular, we formulate consistent and adjoint consistent DG methods
for the numerical approximation of both the compressible Euler and
Navier-Stokes equations; in the latter case, the viscous terms are
discretized based on employing an interior penalty method. By
exploiting a duality argument, adjoint-based a posteriori error
indicators will be established. Moreover, application of these
computable bounds within automatic adaptive finite element algorithms
will be developed. Here, a variety of isotropic and anisotropic
adaptive strategies, as well as hp-mesh refinement will be
investigated.
The outline of these notes is as follows. In Section~2 we give an
introduction to the adjoint-based a posteriori error estimation and
mesh refinement for linear problems, and their subsequent exploitation
within an automatic adaptive finite element algorithms. Then, in
Section~3 we introduce both the compressible Euler and Navier-Stokes
equations and formulate DG numerical methods for their
discretization. In particular, here we will be concerned with the
derivation of so-called adjoint consistent methods, which ensure the
optimal approximation of target functionals of the underlying
solution. Section~4 is devoted to the derivation of adjoint-based a
posteriori error bounds for the computed error in a given target
functional of interest. Moreover, extensions to the case when there
are multiple quantities of interest will be considered. The practical
performance of these a posteriori error estimates within adaptive
finite element algorithms will be studied through a series of
numerical experiments. In Section~5 we consider the generalization of
the above ideas to the case when anisotropic mesh refinement is
permitted. In this setting, we derive both a priori and a posteriori
error bounds for the DG approximation of linear functionals of the
underlying analytical solution. The a priori analysis is fully
explicit in terms of the anisotropy of the underlying computational
mesh. Further, we introduce an anisotropic refinement algorithm, based
on choosing the most competitive subdivision of a given element from a
series of trial (Cartesian) refinements. The extension of these ideas
to general anisotropic hp-version DG finite element methods is
undertaken in Section~6. Finally, Section~7 is devoted to the
application of goal-oriented adaptive finite element algorithms to
complex aerodynamic flows, including three dimensional laminar flows
as well as two and three dimensional turbulent flows
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
L'impact de l'activité humaine sur la composition chimique de la troposphère au-dessus de l'Océan Pacifique: développement d'un modèle téléscopique de chimie et de transport atmosphériques et interprétation des résultats de la campagne de mesure MLOPEX
No full text<p align='justify'>De manière à mieux comprendre l'impact des émissions anthropiques sur la troposphère reculée, les concentrations d'un nombre important de composés atmosphériques ont été mesurés dans la troposphère libre au-dessus d'Hawaii durant la campagne Mauna Loa Observatory Photochemistry Experiment (MLOPEX) accomplie au cours des années 1991 et 1992. Le constituant chimique fondamental pour évaluer cet impact est le radical hydroxyle OH qui fut mesuré au printemps et en été de l'année 1992. La variation diurne de la direction du vent génère pendant la journée un mélange des masses d'air de la couche limite planétaire avec la troposphère libre. Actuellement les modèles régional et global de chimie troposphérique ne peuvent tenir compte à la fois du transport à grande échelle et du mélange local. Nous avons développé un modèle tridimensionnel qui nous permet d'analyser la chimie et la dynamique troposphérique à ces deux échelles. Pour ce faire, nous avons utilisé une grille non-structurée qui offre un moyen efficace de caractériser la région d'Hawaii à l'aide d'une haute résolution et le restant de l'hémisphère Nord avec une résolution qui décroît au fur et à mesure que l'on s'éloigne d'Hawaii. La distribution de 46 composés gazeux avec 138 réactions, incluant une chimie détaillée des hydrocarbures non-méthaniques (isoprène, éthane, éthène, propène et alpha-pinène) est calculée avec un pas de temps de 20 minutes. A l'aide de notre modèle nous avons simulé une période de huit jours pour chacune des saisons. Les résultats des simulations ont été comparés aux observations et interprétés à l'aide d'études de rétro-trajectoires, de traceurs passifs et de bilans chimiques local et régional de l'ozone et de ses précurseurs.</p><p><p>Doctorat en sciences appliquéesinfo:eu-repo/semantics/nonPublishe
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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