1,720,956 research outputs found
An unstructured, three-dimensional, shock-fitting solver for hypersonic flows
No full textA novel unstructured shock-fitting algorithm for three-dimensional flows is presented in this paper. The fitted shock front is described using a double-sided, triangulated surface. Two sets of flow states, corresponding to the upstream and downstream sides of the discontinuity, are assigned to the gridpoints located on either side of the triangulated shock surface. This is allowed to move, while obeying to the Rankine-Hugoniot jump relations, throughout a background tetrahedral mesh which covers the entire computational domain. At each time step, a local, constrained Delaunay tetrahedralization is applied in the neighbourhood of the shock front to ensure that the triangles, which make up the shock surface, are part of the overall tetrahedral grid. The fitted shock surface acts as an interior boundary for a shock-capturing solver that is used to solve the discretized governing equations in the smooth regions of the flowfield. Despite the intrinsic complexity of the algorithm and the need to include the extra computational nodes that make up the triangulated shock-surface, the algorithm is shown to provide high quality results even with the coarse grain tetrahedralizations used in the example provided. Moreover, the re-meshing step is limited to the region close to the shock surface and the fitting algorithm is only weakly coupled with the flow solver used in the simulation. The newly described algorithm is herein tested against an available reference solution which involves the hypersonic (M∞ = 10) flow past a blunt-body featuring a spherical nose. © 2010 by the authors
Numerical simulation of hypersonic flows past three-dimensional blunt bodies through an unstructured shock-fitting solver
No full textOwing to the maturity nowadays reached by computational geometry, shock-fitting, i.e. treating shock waves as true surfaces of discontinuity may no longer be prohibitively complex, as commonly believed by CFD practitioners. In this paper we report on some newly implemented features and algorithmic improvements of an unstructured, shock-fitting algorithm for three-dimensional flows that has been recently proposed by the authors. The shock wave is described using a double-sided triangulated surface which is allowed to float over a background tetrahedral grid while obeying to the Rankine-Hugoniot jump relations. A constrained, Delaunay tetrahedralization is applied in the neighbourhood of the shock-front to make sure that the triangular faces that make up the shock surface are part of the tetrahedral mesh that covers the entire computational domain. A shock-capturing, vertex-centred solver is used to discretise the governing PDEs in the smooth regions of the flow-field; it also allow to ``capture'' those shock waves that may not have been fitted and/or the interaction between different fitted shock surfaces. The capabilities of the technique are demonstrated by reference to the high speed flow past a blunt-nosed cylinder with a conical flare for which experimental and other numerical results are available. When the technique is compared with shock-capturing on un-adapted meshes of comparable resolution, it is shown that fitting the strong shocks allows to considerably improve the solution quality in the entire shock layer and over the body surface
Numerical Simulations of flows past IXV re-entry vehicle at CRAS
No full textCRAS is taking part to the ESA FLPP program contributing significantly
to the computation of numerical simulations for to the aerothermodynamic
database of the IXV vehicle.
Numerical simulation of hypersonic flows represents surely a
strong point for CRAS. Indeed, in this field CRAS boasts researchers with
long experience and availability of state-of-art software tools. In
addition to this, a new computing technique which promises significantly
improvements in the simulation of flows with strong
shocks is presently under development at CRAS.
The paper is a brief overview of the numerical techniques presently, used
in the contract activities related to the IXV program or under development
at CRAS together with a selection of the most significant results
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
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
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