1,720,962 research outputs found
A Kinetic-Based Model for High-Speed, Monodisperse, Fluid–Particle Flows
Full text linkThree-dimensional (3-D) hyperbolic conservation equations for fully compressible, monodisperse, fluid–particle flows with added mass and fluid-phase pseudoturbulence are proposed. A particle-phase kinetic model is developed that accounts for collisional and frictional terms, as well as added mass and internal energy. Transport equations for 3-D velocity moments up to second order (or total kinetic energy) are closed using a Maxwellian distribution. The resulting two-fluid model is well posed for any fluid–particle material density ratio. The numerical methods associated with the hyperbolic system of equations are designed to fulfill the main features of a compressible two-phase flow solver: capturing sharp particle fronts, preserving contact discontinuities, and ensuring stability in all flow regimes. This is done by employing a combination of an AUSM+up scheme for the particle phase, and a HLLC scheme for the fluid phase. Stability is obtained by keeping the discrete consistency between spatial fluxes and buoyancy-like terms implying derivatives. Test cases involving a high-speed fluid interacting with heavy/light particles are used to demonstrate that the qualitative behavior of the flow dynamics is captured correctly by the model.This is a preprint from Boniou, Victor and Fox, Rodney O. and Laurent, Frédérique, A Kinetic-Based Model for High-Speed, Monodisperse, Fluid–Particle Flows.
doi: http://dx.doi.org/10.2139/ssrn.4388742
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Simulation numérique d'écoulements diphasiques évaporants par des méthodes de capture d'interface raides
No full textHigh fidelity simulation of evaporating two-phase flows is a growing subject with the emergence of multiple solvers and various associated numerical methods.This is a very challenging subject because of the strong discontinuities of flow quantities at the interface that requires attention in the design of numerical methods.For Eulerian sharp methods, several strategies have shown their capability to reproduce the physics without phase change using Volume-of-Fluid (VOF) or Level-Set (LS).With phase change, the interface jumps must account for the mass and heat transfers, which requires far more attention in the design of numerical methods. Few contributions can be found, and dedicated studies are required to reach the same level of understanding as for non-evaporating flows.The objective of this work is to compare possible solutions for simulating such flows with Eulerian sharp methods. To this end, all methods are implemented in the same cartesian-grid solver and share the same unified Low-Mach framework to allow fair comparisons.First, the numerical representation of an interface is investigated for four popular interface capturing methods with up-to-date numerics: the volume of fluid (VOF), the standard level set (SLS), the accurate conservative level set (ACLS), and the coupled level set and volume of fluid (CLSVOF). The comparison is made on canonical cases with imposed velocity field.In this configuration, even if all methods show consistent results with mesh refinement, CLSVOF appears to be the most efficient method, and its versatility could be a strong asset when designing numerical methods.Then, all methods are embedded into the unified low-Mach framework without phase change. This framework includes a sharp transport of the interface, a well-balanced surface tension discretization, and a consistent mass-momentum transport which allows capillary-driven simulations with high-density ratios.Specific attention is given to surface-tension-driven cases, and complex test cases such as droplet collision or shear-induced breakup are investigated.Overall, all methods give comparable results for simple test cases, if the numerical resolution is sufficiently high. For the complex cases, especially for the shear-induced breakup, all methods give very different results, which call for new investigation for the ability of methods to capture the onset of instabilities.Finally, the unified framework is extended to phase change using a two-scalar approach for energy and species equations, for VOF and SLS methods. The new numerical challenges are investigated through numerical experiments to justify the numerical choices made in the unified framework.Specific attention is devoted to the analysis of numerical errors in the reconstruction of interface quantities, showing the importance of extrapolation methods and of evaluating quantities at the interface location.A quantitative analysis is given on canonical evaporation problems for which analytical solutions are available. Both VOF and LS methods show mesh convergence, but with opposite trends for the static evaporation case: while LS overestimates the interface regression, VOF underestimates it.The final test case is a convected droplet in a quiescent flow, which implies convection, interface deformation, and non-homogeneous vaporization. In this case, the importance of the consistency between momentum and continuity is highlighted by considering different techniques of the literature for the continuity equation. It is shown that non-consistent formulations lead to an increased velocity of the droplet. The results for SLS suggest that the shared framework is too constraining, and a dedicated framework must be used. Finally, as VOF equations can be rigorously derived from the conservation equations, there is no ambiguity in the discrete continuity equation, and we consider the results to be representative of the physics.La simulation des écoulements diphasiques évaporant est un sujet en plein essor avec l'émergence de multiples solveurs et méthodes numériques associées.C’est un sujet difficile en raison des discontinuités de l’écoulement à l'interface qui nécessitent des méthodes numériques adaptées.Parmi les méthodes Eulériennes « sharp », plusieurs stratégies ont montré leur capacité à reproduire la physique sans changement de phase, que ce soit en Volume-of-Fluid (VOF) ou en Level-Set (LS).Avec le changement de phase, les sauts d'interface doivent tenir compte des transferts de masse et de chaleur. Peu de contributions existent, et des études spécifiques sont nécessaires pour atteindre le même niveau de compréhension que pour les écoulements sans évaporation.L'objectif de ce travail est de comparer les solutions possibles pour simuler de tels écoulements. Toutes les méthodes sont implémentées dans le même solveur et partagent le même cadre unifié Low-Mach pour permettre des comparaisons équitables.La simulation d'une interface est d’abord étudiée pour quatre méthodes : le VOF, la standard level set (SLS), l’accurate conservative level set (ACLS), et le coupled LS-VOF (CLSVOF). La comparaison est effectuée sur des cas avec champ de vitesse imposé.Dans ce cadre, même si toutes les méthodes présentent des résultats cohérents et convergents en maillage, le CLSVOF semble être la méthode la plus précise, et sa polyvalence pourrait être un atout important pour des cas plus complexes.Ensuite, les méthodes sont intégrées dans le même cadre unifié, sans changement de phase. Ce cadre comprend un transport précis de l'interface, une discrétisation équilibrée de la tension de surface et un transport masse-quantité de mouvement cohérent qui permet des simulations avec un rapport de densité élevé et des effets capillaires.Une attention particulière est accordée aux cas avec tension superficielle, et des cas tests complexes de collision de gouttes ou de rupture induite par cisaillement sont étudiés.Les méthodes donnent des résultats comparables pour les cas simples, si la résolution numérique est suffisamment élevée. Pour les cas complexes, en particulier pour la rupture induite par cisaillement, les méthodes donnent des résultats différents, ce qui nécessite des études sur la capacité des méthodes à saisir le début des instabilités.Enfin, le cadre unifié est étendu au changement de phase en utilisant une approche à deux scalaires pour les équations d'énergie et d'espèces, pour les méthodes VOF et SLS. Les défis numériques sont étudiés numériquement afin de justifier les choix effectués.Une attention particulière est consacrée aux erreurs numériques dans la reconstruction des quantités d'interface, montrant l'importance des méthodes d'extrapolation et de l'évaluation des quantités à l'emplacement de l'interface.Une analyse quantitative est donnée sur les problèmes d'évaporation canoniques avec solutions analytiques. Les méthodes VOF et LS montrent une convergence en maillage, mais avec des tendances opposées pour le cas d'évaporation statique : alors que la LS surestime la régression de l'interface, le VOF la sous-estime.Le dernier cas test est une goutte convectée dans un écoulement au repos, qui implique une convection, une déformation de l'interface et une vaporisation non-homogène. L'importance de la cohérence entre l’équation de quantité de mouvement et de continuité est mise en évidence en considérant différentes techniques de la littérature pour l'équation de continuité, montrant que les formulations incohérentes conduisent à une augmentation de la vitesse de la goutte. Les résultats pour SLS suggèrent que le cadre unifié est trop contraignant, et qu'un cadre dédié doit être utilisé. Enfin, comme les équations VOF peuvent être rigoureusement dérivées des équations de conservation, il n'y a aucune ambiguïté dans l'équation de continuité discrète, et nous considérons que les résultats sont représentatifs de la physique
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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