1,720,955 research outputs found
CFD modelling of breakwaters embedding wave energy converters
Full text linkIn recent years the raising supply and environmental problems related to traditional fossil fuel exploitation for energy production have pushed the research on renewable sources. Among these, sea waves have a high potential, but still poorly used. Different technologies have been developed in order to harness wave energy, and the Oscillating Water Column (OWC) devices are the most accredited for an actual diffusion. This work is focused on the performance analysis of particular OWC-type devices, namely the REWECs (REsonant sea
Wave Energy Converter). Two different versions have been considered, the REWEC1 and the REWEC3, constituting a submerged and an emerged breakwater, respectively. The most interesting aspect of REWECs is the possibility to operate them under resonant conditions with that sea state which is the one that gives the highest yearly energy contribution. Both REWEC1 and REWEC3 dynamic behavior can be approximated by
means of a mass-spring-damper system. According to this approximation, a criterion for evaluating the oscillating natural frequency of the REWECs has been derived. A CFD model has been developed in order to verify the resonance behaviour of a scaled REWEC1 device. The water-air interaction has been taken into account by means of the Volume Of Fluid (VOF) model implemented in the commercial code Ansys Fluent. Both air and water fow felds have been assumed to be unsteady. The CFD model has been validated against
both analytical and experimental results. Simulation results showed a good agreement with both measurements and predictions, particularly when the Standard k-ω turbulence model is implemented inside the REWEC.
The CFD model has been applied also to the simulation of both conventional and REWEC1 submerged breakwater placed into a two-dimensional wave fume, obtaining a novel method for the valuation of the REWEC1 absorption coefcient. In fact, when considering the interaction of waves with a conventional submerged breakwater, the incident wave energy is shared into: a refected fractiona a dissipated fraction, due to the wave breaking and the friction losses on ita and a transmitted fraction to the shore. If the
submerged breakwater embeds a REWEC1, a further reduction of the transmitted energy can be achieved due to device absorption, improving the coast protection performance of the structure. Actually, a scaled REWEC1 breakwater without PTO-system (Power Take-Off) has been considered. Then, the simulation results showed only a small difference between the transmission coefcients of the two breakwaters, allowing however to calculate
the absorption coefcient of the REWEC1 due to the water losses inside the device. Finally, a full-scale REWEC3 breakwater has been simulated by means of CFD, taking into account the characteristics of the air turbine adopted as power take-off device. The breakwater replicated the one installed in the Civitavecchia harbour (Italy). A typical sea state has been reproduced by means of regular waves generated by a piston-type wave-maker. As in the case of the scaled REWEC1, CFD unsteady simulation have been carried out in a two dimensional (2D) reference frame, reducing the huge need of computational resources. In order to simulate the oscillating fow across the air turbine, a new method has been also proposed here. The zone of the domain corresponding to the duct where the air turbine is embedded has been modelled as a porous zone. Analytical equations able to model the exchange of mass and energy across the air duct and the turbine have been
implemented. The simulation results are in good agreement with the ones registered during the operation of the Civitavecchia plant. A further outcome of the work has been a deep insight into the fuid-dynamic behaviour of the water fow inside the REWEC3, highlighting the design improvements needed to reduce friction losses
CFD analysis of the wave interaction with both a submerged impermeable breakwater and one embedding an OWC device
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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
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
Numerical prediction of the natural frequency of an Oscillating Water Column operating under resonant conditions
Full text linkAmong the different technologies developed in order to harness wave energy, the Oscillating Water Column devices are the most accredited for an actual diffusion. Recently, Boccotti has patented the REWEC1 (REsonant sea Wave Energy Converter solution 1), a submerged breakwater that performs an active coast protection, embedding an Oscillating Water Column device, which is capable of operating under resonant conditions with that sea state, which gives the highest yearly energy contribution. The REWEC1 dynamic behavior can be approximated by means of a mass-springdamper
system. According to this approximation, a criterion for evaluating the oscillating natural frequency of the REWEC1 has been derived. This criterion has been validated against both experimental results and computational fluid dynamics simulations, performed on a REWEC1 laboratory-scale model. The numerical simulations have shown a good agreement between measurements and predictions
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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