1,721,049 research outputs found
Small scale localization in turbulent flows. A priori tests applied to a possible Large eddy Simulation of compressible turbulent fllows
No full textA method for the localization of small scales in turbulent velocity fields is proposed. The method is based on the definition of a function f of the velocity and vorticity fields that reproduces a normalized form of the twisting-stretching term of the Helmholtz equation. By means of this method the equations of motion can be selectively filtered in regions that are rich in small scale motions. The method is applied through a criterion built on a statistical link between the function f and a local property of the turbulence that was derived from the analysis a homogeneous and isotropic high Reynolds number (Reλ = 280) turbulence field. The localization criterion is independent of the subgrid scale model used in a possible Large Eddy Simulation carried out after the small scale localization is obtained. This extends the typology of possible applications to the analysis of experimental laboratory data. In case of compressible regimes, a second sensor that depends on the local pressure variation and divergence can be associated to the previous one in order to determine the eventual emergence of shocks. The capture of shocks is made possible by suppressing the subgrid terms where this second sensor indicates the presence of a shock. A priori tests were carried out on the turbulent channel flow, Reλ = 180 and 590, to validate the localization procedure in a highly inhomogeneous flow configuration. A second set of a priori test was carried out on a turbulent time decay which reproduces a few hydrodynamical properties of high Reynolds number hypersonic jets which exist in the Univers
Ecological and economic indicators for the evaluation of almond (Prunus dulcis l.) orchard renewal in sicily
Full text linkGlobally, almond production is experiencing a growing trend thanks to a strong interest in the health, gastronomic, and industrial properties that are linked to the fruits and their derivatives. After a constant and marked decline in the second half of the last century, the Mediterranean Basin is thoroughly reassessing this crop, which provides significant results with a modern orchard management. The opportunity determined by the transition from traditional to modern systems have increased the interest in evaluating the different environmental impacts of the two cultivation models that still coexist today. In this work, through the application of the Life Cycle Assessment (LCA) and an economic assessment approach with an in-depth analysis related to the cultivation cycle and the use of resources, the role played by each factor involved in production was determined. Overall, the Greenhouses Gases (GHG) emissions in modern farms are higher (Global Warming Potential (GWP) 0.224 kg CO2 eq.) than those in traditional farms (GWP 0.182 kg CO2 eq.). Regarding the economic assessment, it appears relevant that the modern almond model in the full production phase guarantees significantly higher margins (+84%).The perception of the importance attributed to evaluating economic and environmental aspects by different stakeholders shows relevant differences in the approach coming from growers, dealers, and governmental institutions allows the investigators to positively underline the current innovation in almond orchard systems considering the balance between fruit production and the conservation of environmental resources
Large-eddy simulation of hypersonic flows. Selective procedure to activate the sub-grid model wherever small scale turbulence is present
Full text linkA new method for the localization of the regions where small scale turbulent fluctuations are present in hypersonic flows is applied to the large-eddy simulation (LES) of a compressible turbulent jet with an initial Mach number equal to 5. The localization method used is called selective LES and is based on the exploitation of a scalar probe function! which represents the magnitude of the stretching tilting term of the vorticity equation normalized with the enstrophy (Tordella et al., 2007) [3]. For a fully developed turbulent field of fluctuations, statistical analysis shows that the probability that f is larger than 2 is almost zero, and, for any given threshold, it is larger if the flow is under-resolved. By computing the spatial field off in each instantaneous realization of the simulation it is possible to locate the regions where the magnitude of the normalized vortical stretching tilting is anomalously high. The sub-grid model is then introduced into the governing equations in such regions only. The results of the selective LES simulation are compared with those of a standard LES, where the sub-grid terms are used in the whole domain, and with those of a standard Euler simulation with the same resolution. The comparison is carried out by assuming as reference field a higher resolution Euler simulation of the same jet. It is shown that the selective LES modifies the dynamic properties of the flow to a lesser extent with respect to the classical LES. In particular, the prediction of the enstrophy, mean velocity and density distributions and of the energy and density spectra are substantially improved
Localization of unresolved regions in the selective large-eddy simulation of hypersonic jets
Full text linkA method for the localization of the regions where the turbulent fluctuations are unresolved is applied to the selective large-eddy simulation (LES) of a compressible turbulent jet of Mach number equal to 5. This method is based on the introduction of a scalar probe function f which represents the magnitude of the twisting-stretching term normalized with the enstrophy [1]. The statistical analysis shows that, for a fully developed turbulent field of fluctuations, the probability that f is larger than 2 is zero, while, for an unresolved field, is finite. By computing f in each instantaneous realization of the simulation it is possible to locate the regions where the magnitude of the normalized stretching-twisting is anomalously high. This allows the identification of the regions where the subgrid model should be introduced into the governing equations (selective filtering). The results of the selective LES are compared with those of a standard LES, where the subgrid terms are used in the whole domain. The comparison is carried out by assuming as high order reference field a higher resolution Euler simulation of the compressible jet. It is shown that the selective LES modifies the dynamic properties of the flow to a lesser extent with respect to the classical LE
Experiments and numerical simulations on the mid-term evolution of hypersonic jets; Astrophys. Space Sci.
No full textConsumare latte in maniera sostenibile: Il ruolo congiunto di variabili socio-psicologiche e della valutazione degli attributi intrinseci ed estrinseci del prodotto
No full text
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
- …
