1,721,101 research outputs found
Interactions between swell and colinear wind short crested waves, following and opposing
No full textWhen wind blows over a water surface during a swell, it generates short-crested, three-dimensional waves that interact with the underlying flow field through a mechanism that ultimately increases the average energy. In the present work, two test cases in which wind is flowing following and opposing a swell are analysed with experiments and are compared with wind-waves-only and swell-only cases. The analysis of the free surface fluctuation and of the flow field, with the three components of fluid velocity measured at the same time through a stereo particle image velocimetry system, leads to an accurate quantification of the energy distribution, of the structure of the oscillating, fluctuating (due to wind-waves) and turbulent kinetic energy, without assumptions on the structure of the flow. The findings demonstrate that the transverse dynamics is a pivotal factor in the transfer of energy in the near-free surface domain, and elucidate the energy transfer between wind-waves and swell. The results also confirm the reduction of oscillating kinetic energy of the swell in the presence of short wind-waves, a process interpreted with different possible mechanisms. There is evidence of the enhancement of wind action in the presence of swell compared to that in the case of wind-waves-only, confirming that energy transfer from the wind to the sea is enhanced when wind flows over a swell. Consequently, when the fetch is influenced by swells generated or propagated from different regions, and during multi-peak sea storms, wave generation models should account for this amplification
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
Theoretical approach to the scale effects of an OWC device
No full textThis research deals with the dynamic similarity problem for Oscillating Water Column (OWC) devices, for
which air is the fluid that is subject to thermodynamic transformations in the inhalation/exhalation phases.
Based on the differential problem, both linearized and full-nonlinear, the scale ratios satisfying similarity are
calculated, with specific reference to the case where constraints are present on some of these scale ratios.
The paper proceeds to identify the numerous processes of a turbulent interface that scales differently between
model and prototype. With the aim of bringing to front the influence of the scale effects on featured aspects
of the thermodynamic process involved, it is proposed that a non-equilibrium thermodynamics approach can
be more comprehensive and representative not only of transformations, but also of scaling. The study reveals
that in the case of OWC thermodynamics, non-equilibrium states which would be less evident in scaled model,
would become more relevant as the scale is increased towards the size of the prototype, with consequences
on performance
3D flow measurements in regular breaking waves past a fixed submerged bar on an impermeable plane slope
Full text linkThe velocity fields induced by regular breaking waves past a fixed bar on a 1:10 rigid plane slope were measured and analysed using a volumetric particle-tracking velocimetry system. Under specific conditions, the wave-mophological features interaction steepens the waves which eventually breaks. The geometry of the boundaries of the present experiments is common in natural environments, where reefs, sand and gravel bars, and submerged coastal structures, interact with the incoming wave field 'affecting' the transport budget of substances (sediment, nutrients and pollutants), with relevant consequences on the water quality. The aims of the present work are the analysis of the flow field in the breaker, the quantification of the terms in the equations usually adopted for modelling the flow and the turbulence. Two sets of attacking monochromatic wave trains with different periods and heights were used to generate a dataset of instantaneous velocity, which was further analysed to extract turbulence. The measurement volume extended
from the wave crest to a portion of the domain below the wave trough. The balance of linear momentum for the average field and the balance of turbulence, were scrutinised and included all the terms in a 3D approach. The analysed data and results are original and novel because they include all the contributions derived from the 3D structure of a real flow field, and constitute a huge data set for calibration of numerical codes
Phase-resolved analysis of velocity field structure and vorticity dynamics under colinear swell and wind-waves
No full textThe objective of this study is to analyze the turbulence field generated by the interaction between mechanical waves and colinear wind-waves in the liquid domain just below the free surface. Detailed three-dimensional velocity measurements close to the surface are decomposed into mean, swell, wind-waves, and turbulence contributions. In this work, we treat wind-waves as macroscale turbulence with a pseudo-random velocity field. Advanced data analysis yields phase-resolved and vertical examinations of wind-waves and turbulence stresses, kinetic energy, and vorticity. The results indicate that near the surface, the spanwise energy dominates both the wind-wave and the turbulence kinetic energy. The wind-waves and turbulence stress tensors exhibit a large anisotropy when swell waves are present, as a consequence of the interaction between swell and wind-waves. Furthermore, we present the spatio-temporal distribution of vorticity, and we elucidate the non-trivial interaction between vorticity and the flow field. This interaction results in body forces that contribute to the local variation in inertia, as described by the Navier–Stokes equation. It is observed that in all combinations, a body force acts, on average, downward, modifying the gradient pressure in the vertical direction
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
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