1,720,955 research outputs found
Large Eddy Simulation of Suspended Sediment In Turbulent Open-Channel Flow
No full textThis study aims to shed light on the dark sides of sediment transport and meandering channel flow patterns. For this purpose, the Large Eddy Simulation methodology was used to investigate sediment transport in open-channel flow and also to predict the meandering channel flow pattern in two sine-generated channels.
In the turbulent flows the transported suspended sediments is usually assumed in a passive form. In other word, the feedback effect of sediment suspension on near-wall momentum transport is neglectable. The first phase of this research was devoted to quantify the just mentioned effect in the open channel flow. A single phase approach was used to gain better description of sediment-turbulence interaction. The contribution of the small scales was parametrized by a dynamic Smagorinsky model. Results revealed that - in presence of large suspension- the buoyancy effect modifies the dynamics of flows.
The second phase of the research was dedicated to the turbulent flow in meandering channels. These channels had initial deflection angles of 45 and 95 degrees. In both cases the width-to-depth ratio was equal to 15. The super-elevation of water in channel, which is impressed by secondary motion in the meandering channels, was considered in the numerical model. Analysis of numerical results was carried out on the basis of both instantaneous and time-averaged velocity fields. In addition, to provide an accurate description of the mean flow, this work explored the characterization of the cross-circulatory motion and the internal turbulence structure of flows. In particular, the sediment transport was investigated in the meandering channel to clarify the effect of bed shear stress variation induced by the channel curvature
Large eddy simulation of two-way coupling sediment transport
No full textIn the present paper numerical simulations are used to investigate suspended sediment transport and its effect on the dynamics of the turbulent boundary layer. We use an Euler–Euler methodology based on single-phase approach. Large eddy simulation is employed to resolve the large scales of motion, whereas
the contribution of the small scales is parametrized by the use of a dynamic Smagorinsky model. In order to account for sediment-induced buoyancy on momentum, a buoyancy term is considered in the threedimensional Navier–Stokes equations through the use of the Boussinesq approximation. We consider
four sediment sizes and the simulations are performed for both one-way and two-way coupling approaches to gain a better description of sediment–turbulence interaction. The level of stratification for each particle size is qualified by the bulk Richardson number which increases by decreasing the grain
size. The analysis reveals that the reduction of sediment size produces a larger suspension and sediment concentration in the flow field, due to the concurrence of increased available concentration at the wall and reduced deposition velocity. Comparison of concentration profiles between one-way and two-way
coupling clearly shows the remarkable effect of stratification on the velocity and concentration mean profiles. This is particularly true for small sediments which are more likely suspended in the fluid column. In agreement with experimental literature results, our study shows that suspended sediment concentration
reduces the von Kàrmàn constant of the velocity profile. The analysis of second order statistics and energy power spectra show turbulent suppression due to stratification effects, in agreement with previous studies. The gradient Richardson number distribution along the channel height demonstrates the
increased level of stratification along the fluid column by decreasing the grain size. Momentum and concentration diffusivity are also discussed. The non-dimensional concentration diffusivity compares very well with the Coleman’s experimental data in the range of parameters shared by the two studies. Overall,
the results of our study confirm that a single-phase mathematical model is a good candidate to simulate suspended sediment transport. Our study also shows that differences between one-way and two-way coupling approaches are negligible for relatively large sediments, that, on the other hand, are more likely
transported according to the bed-load mode. For smaller particles, transported according to the suspension-load mode, the two-way coupling approach reproduces the reduction of turbulence activity already observed in physical experiments
Large Eddy Simulation of suspended sediment transport
No full textMathematical models of sediment transport usually assume the sediment particles as passive
tracer and neglect the feedback effect of sediment resuspension on near-wall momentum transport.
In the present research we attempt to quantify the above mentioned effect with the aim of gaining better
description of sediment-turbulence interaction. We carry out Large Eddy Simulations (LES) of noncohesive
sediment transport in open channel flow at Re= 600. The simulations are based on the singlephase
approach in which the sediment phase is treated using an advection-diffusion transport equation
for the sediment concentration. The flow over the sediment bed obeys the incompressible 3D Navier-
Stokes equations under the Boussinesq approximation for buoyancy effects. Two-way coupling model is
employed where the effect of suspended sediments on flow field is considered as density variation in gravity
term of Navier-Stokes equation. Analysis of simulation results is carried out based on time-averaged
profile of streamwise velocity and concentration field for both one-way and two-way coupling models.
In presence of high suspended sediments in water column, the averaged concentration profiles reveal
significant difference between one-way and two-way coupling approach due to buoyancy effects. It is
remarkable that feedback effects are negligible in case of large grain size when the reference concentration
is small at the wall and deposition flux is large. The time-averaged streamwise velocity profile shows that
stratification effects reduce the von-karman constant which is in agreement with previous studies. The
visualization of instantaneous low-speed streaks is also confirmed the stratification effects on the near
wall region
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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