1,721,036 research outputs found
Closure to "new Approach to Predicting Local Scour Downstream of Grade-Control Structure" by M. Ben Meftah and M. Mossa
No full textNew Approach to Predicting Local Scour Downstream of Grade-Control Structure
No full textDespite the numerous studies on scouring processes, the prediction of scour-hole dimensions downstream of hydraulic structures remains challenging because of the complexity of the phenomenon and its dynamic sensitivity to structure and sediment properties. This study experimentally focuses on scour-hole development downstream of a sloped grade-control structure (GCS) in alluvial channels. A large series of laboratory experiments were carried out in a rectangular channel with a noncohesive sediment bed. Based on the data from this study and data collected from previous studies, the effect of the downstream face slope of a GCS on scour morphology was analyzed. In this regard, it was found that the face slope has an effect only if it is smaller than the slope of the upstream equilibrium scour side obtained with a GCS of a vertical downstream face. Before reaching an equilibrium state, the scour process evolves into three distinct phases, a very rapid initial phase, an intermediate gradual phase, and an equilibrium phase. A general empirical expression for predicting temporal scour evolution is proposed and extended to different types of GCS. Moreover, a new scaling approach is proposed that leads to the derivation of new equations predicting equilibrium scour profiles with different entering jet-flow typologies. To make these equations operational, a series of estimating expressions for the characteristic lengths of equilibrium scour holes is also proposed
Flow Hydrodynamic in Open Channels: A Constantly Evolving Topic
No full textStreams and riverbeds are subject to considerable hydromorphological alterations due to the interaction of their flow with natural or man-made structures found throughout them, i [...
Experimental investigation on dispersion mechanisms in rigid and flexible vegetated beds
No full textVegetation in channels strongly affects flow structure and turbulence, with consequences on the hydrological storage of nutrients and chemical tracers, the shelter of stream biota as well as the trapping or transport of sediments. At the same time, all these phenomena are inevitably subjected to alteration of hydrological conditions in fluvial systems due to climate change. The present study intends to provide a thorough investigation into the processes of transport and dispersion induced by flow turbulence within the vegetation structure. Specifically, velocity measurements in vegetated channels were intensively conducted and analyzed in the case of both flexible submerged and rigid emergent canopies. The experiments aimed to: (i) highlight the differences in the hydrodynamic structures induced by different plant types and configurations; (ii) study the spatially varying dispersive properties and turbulent behavior of the current, attributable to different plant density, submergence and stiffness. Further, the spatial variability of velocity and turbulence distributions was taken into due consideration. The experimental results showed how longitudinal and transversal hydrodynamics and transport differ, depending on vegetation configuration and stem properties
Wave and turbulent Reynolds stresses in irregular shoaling waves
No full textThe dynamics of regular breaking waves has been both widely and successfully
investigated. In any case, many natural coastal processes are commonly due to
irregular breaking waves, the behaviour of which requires thorough study. The
present research aims to investigate the distributions of the wave and turbulent
Reynolds shear stresses in a laboratory irregular wave, characterized by a narrow
banded spectrum, which develops on a sloping sand bottom, in intermediate waters.
Experiments focused on the wave shoaling region, in order to analyze the effects of
breaking induced turbulence outside the surf zone, taking into account that
turbulence is not limited to the breaking region but it spreads also outside the surf
zone. The phase-averaging technique was used to separate the turbulent components
from the steady ones. All the analysed values derive directly from real
measurements and are not interpolated. Moreover, a 3D Acoustic Doppler
Velocimeter was adopted to measure the wave velocity, consequently the longshore
component of the velocity is also available to estimate the shear stresses. These
experimental data were also used to test some literary numerical models and
relevant results have been obtained, which confirm the outputs of the
abovementioned models in the cases of non dissipative waves propagating above a
flat bottom and dissipative waves propagating over a sloping bottom
Vegetation effects on vertical jet structures
No full textThis paper deals with measurements of the three-velocity components of a vertical, round, turbulent jet discharged into a vegetated cross flow. Over the last years, a large number of experimental studies and numerical models on turbulent jets discharged into a cross flow have been carried out, as well as several studies on vegetated channels. However, these studies show a lack of data regarding the combination between the vegetated channels and jets. The present study aimed at obtaining a more thorough understanding of the vegetation effects on the jet behaviors. To simulate the vegetation, arrays of emergent, rigid, circular steel cyl-inders were used. The jet source was placed at the centre of the experimental vegetated area. The time-averaged velocity field was investigated in the longitudinal, cross and horizontal planes of the channel. The results show that vegetation has significant effects on the jet structure as compared with the case of non-vegetated channel. Above all, the rigid stems reduce streamwise velocities, giving rise to an increase of the jet penetration height within the ambient flow. Moreover, the familiar pair of counter-rotating vortices and kid-ney shape observed in the cross section of the jet discharged into the non-vegetated channel disappears and transforms under the effects of stems into a complex flow motion structure for the jet discharged into the vegetated flume
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
- …
