1,720,967 research outputs found
Three-dimensional coarse large-eddy simulations of the flow above two-dimensional sinusoidal waves
No full textLarge-eddy simulations (LES) of the flow over two-dimensional sinusoidal waves with a very low grid resolution are presented. A dynamic two-parameter subgrid scale (SGS) model is employed. A configuration characterized by a wave length of 0.6096 mi a maximum slope of 0.497, and a bulk velocity of 10 m s(-1) is initially considered. Comparisons with experimental data, and with the results of a previous LES ms show that. in spite of the very low grid resolution, the mean flow and both the viscous and the pressure drag forces are well predicted. Some details of the flow, such as the presence of a secondary flow, are also captured. Thus, additional LES are carried out to investigate the effect of the Reynolds number (Re), and of the wave amplitude. In particular, the dependence of viscous and pressure drag on these parameters is studied and compared with the results of similar analyses in the literature
Drag prediction over steep sinusoidal wavy surfaces
No full textA parametrization of the form drag due to airflow over sinusoidal wavy surfaces in the presence of significant flow separation is investigated; it is based on a bluff-body analogy. To this aim, the results of large-eddy simulations carried out for various Reynolds numbers and wave slopes are used, together with the data from experiments and other simulations available in the literature. It is shown that, as a first approximation, the drag coefficient may be considered independent of the wave slope and Reynolds number. The value obtained here for rigid sinusoidal waves is close to that computed for wind-ruffled breaking paddle waves
Towards the simulation of cavitating flows in inducers through a homogeneous barotropic flow model
No full textNumerical Experiments with an Homogeneous-Flow Model for Thermal Cavitation
Full text linkAn homogeneous cavitation flow model capable of accounting for both the effects of thermal cavitation and the concentration of the active nuclei is considered; the model results in a barotropic state law. The local presence of both incompressible zones (pure liquid) and regions where the flow may become highly supersonic (cavitating mixture) renders the problem particularly stiff from a numerical viewpoint. The continuity and momentum equations for compressible inviscid flows are considered together with the barotropic state law. They are discretized by a finite-volume formulation applicable to unstructured grids. A shock-capturing upwind scheme is proposed for barotropic flows. The accuracy of the proposed method at low Mach numbers is ensured by ad-hoc preconditioning, which only modifies the upwind part of the numerical flux; thus, the time consistence is maintained and the proposed method can also be used for unsteady problems. Finally, an implicit time advancing is proposed to avoid severe time-step limitations encountered with explicit schemes. The proposed CFD tool is validated by quasi-1D simulations of nozzle flow
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
Numerical Simulation of the Flow in a Turbopump Inducer in Non-Cavitating and Cavitating Conditions
No full textA numerical methodology for the simulation of cavitating flows in real complex geometries is presented. A homogeneous-flow cavitation model, accounting for thermal effects and active nuclei concentration, which leads to a barotropic state law is adopted. The continuity and momentum equations are discretized through a mixed finite-element/finite-volume approach, applicable to unstructured grids. A robust preconditioned low-diffusive HLL scheme is used to deal with all speed barotropic flows. Second-order accuracy in space is obtained through MUSCL reconstruction. Time advancing is carried out by a second-order implicit linearized formulation together with the Defect Correction technique. The flow in a real 3D inducer for rockets turbopumps is simulated for a wide range of conditions: different flow rates and rotating speeds as well as non-cavitating and cavitating flows are considered. The results obtained with this numerical approach are compared with experimental data
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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