1,720,988 research outputs found
Estimated generalized dimensions of river networks
No full textThis work concerns a numerical estimation of the generalised fractal dimension of six river networks in Southern Italy, extracted from digitised maps on a 1:25,000 scale. The estimation is carried out through the method introduced by Pawelzik and Schuster, based on an extension of the correlation integral by Grassberger and Procaccia. We analysed the spectra of the generalised dimensions Dq and the multi-fractal spectra f(α). The results are in agreement with the ones previously obtained through the use of standard box-counting techniques: they indicate that the investigated river networks are multi-fractal structures, with support dimensions ranging between 1.7 and 1.9, and appear not to be plane-filling sets. In the case of the Corace river, the multi-fractal spectrum of the whole river network approaches the envelope of the spectra of substructures corresponding to different hortonian stream orders. © 2005 Elsevier B.V. All rights reserved
A study of vortical structures past the lower portion of the Ahmed car model
No full textVortical structures that develop past the lower portion of the Ahmed car model (in the φ{symbol} = 25o slant-angle configuration) have been studied numerically. Numerical simulations are executed (at ReL = 2.88 × 106) by means of a finite-volume computational code following the LES approach, and the results are compared with the experimental data obtained by other authors at the same value of the Reynolds number. For further investigation of the flow fields, the method of the imaginary part of the complex eigenvalue pair of the velocity-gradient tensor (λci or swirlingstrength criterion) is applied to the velocity field to extract the turbulence vortical structures. As a result we found that vortical structures of arch type generate from the lower portion of the body, in particular the plane-channel-type zone that is included between the floor of the computational domain and the external side of the body bottom characterized by alternatively high and low turbulent kinetic-energy contents
Indagine mediante tecniche a taglia fissa sulla struttura multifrattale delle reti fluviali
No full textFlow structures around a large-diameter circular cylinder
No full textIn ocean and coastal engineering, a widely used tool for the investigation of wave phenomena is the velocity potential, in which both hypotheses of inviscid fluid and irrotational flow are incorporated. In some cases, a close-form analytical expression of the potential can be devised. In other cases, and especially in complex problems of contemporary engineering, no expressions of the potential exist, so that the system of the Euler equations - cast in terms of the potential - is solved numerically, usually by means of numerical techniques of integral nature. It can though be recognized that the assumptions of both inviscid fluid and irrotational flow are rather restrictive. Within this class of problems, if one wants firstly (mainly due to limited computing power available) to give up one of the two previous hypothesis - namely, that of irrotational flow - an appropriate strategy for the investigation of wave-related phenomena is represented by the numerical integration of the Euler equations in the velocity-pressure formulation. Under this viewpoint it becomes of remarkable importance to investigate the differences that exist between a flow field derived from a velocity potential and one resulting from the numerical solution of the Euler equations in primitive variables, as related to the wave case at hand. In this work these issues - relatively unexplored in the literature - are addressed, with reference to the case of the diffraction of water waves caused by a large-diameter, surface-piercing, vertical circular cylinder. The close-form velocity potential for this problem is first analyzed, as related to a number of strictly linear wave cases. Then, some of these cases are simulated numerically by solving the Euler equations in primitive variables, and the results are compared. For further investigation of the flow fields, the swirling-strength criterion for flow-structure extraction is applied to the velocity fields related to one of the wave cases examined. It is found that, in terms of flow structures, remarkable differences exist between the differently derived flow fields
Reliability of 5-beam LDV fiberoptic probe for turbulence measurements in the wall region of open-channel flow
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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
Multifractal analysis of rainfall time series: uncertainty assessment and drawbacks through different fixed-size techniques.
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