1,720,973 research outputs found
A pressure–velocity jump approach for the CFD modelling of permeable surfaces
Full text linkPermeable surfaces are extremely common in applications, ranging from wind shields installed on bridge decks to the outer layer of permeable double skin facades. However, due to the large scale separation between the overall dimensions of the structure and the size of the pores, their modelling in Computational Fluid Dynamics, CFD, simulations are still extremely problematic. In particular, explicitly modelling the pores geometry leads to prohibitive computational costs, while homogenized models based on the use of so-called pressure-jumps are often very crude simplifications of their aerodynamic behaviour. In this paper, a novel approach based on the use of pressure–velocity jumps, PVJ, is proposed. Firstly, the approach is deduced in a general form, based on mass and momentum conservation across the permeable surface. Then, some limit cases for which an analytical evaluation of the coefficients characterizing the model can be obtained are discussed. Finally, a ground mounted barrier is modelled, considering permeable surfaces of widely different aerodynamic behaviour. Results obtained modelling the barrier geometrical details and using the proposed PVJ approach are compared, confirming the soundness of the proposed approach. An OpenFOAM boundary condition implementing the proposed method is available at https://site.unibo.it/cwe-lamc/en
Low-fidelity simulations in Computational Wind Engineering: shortcomings of 2D RANS in fully separated flows
No full textComputational Wind Engineering has rapidly grown in the last decades and it is currently reaching a relatively mature state. The prediction of wind loading by means of numerical simulations has been proved effective in many research studies and applications to design practice are rapidly spreading. Despite such success, caution in the use of simulations for wind loading assessment is still advisable and, indeed, required. The computational burden and the know-how needed to run high-fidelity simulations is often unavailable and the possibility to use simplified models extremely attractive. In this paper, the applicability of some well-known 2D unsteady RANS models, particularly the k-ω SST, in the aerodynamic characterization of extruded bodies with bluff sections is investigated. The main focus of this paper is on the drag coefficient prediction. The topic is not new, but, in the authors' opinion, worth a careful revisitation. In fact, despite their great technical relevance, a systematic study focussing on sections which manifest a fully detached flow configuration has been overlooked. It is here shown that the considered 2D RANS exhibit a pathological behaviour, failing to reproduce the transition between reattached and fully detached flow regime
Simulation strategies for wind shields and porous barriers for bridge deck optimization
No full textWind shields and porous barriers are often positioned on bridge decks as ancillary structures. While being
irrelevant from the structural point of view, it is well-known that their presence can deeply affect the deck
aerodynamic performance. In particular, not only do they generally lead to an increase of the drag force, but also
they modify the overall flow arrangement, so affecting all aerodynamic coefficients. In this paper, the numerical
simulation of porous elements positioned on bridge sections is addressed following two approaches: in the first
one, the pores are explicitly modeled, while in the second one a more convenient pressure-jump approach is
adopted. In particular, the second approach has strong advantages compared to the first one, especially when
simulations are used for optimization. The results obtained using these approaches are compared with each other
and experimental measurements, highlighting strengths and limitations of both methodologies
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
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