1,720,991 research outputs found
Performance Study of Helical Darrieus Rotor
No full textNowadays, electrical power is crucial for all human activities. Several methods are available to produce the electrical energy. Small-scale hydropower is designated as a clean and renewable energy resource that maintain the biodiversity of natural environment. Hydrokinetic rotors are broadly classified based on the rotation axis into two major categories, horizontal axis hydrokinetic rotors and vertical axis hydrokinetic rotors. Although horizontal axis hydrokinetic rotors remain to be commercially appropriate for large-scale hydropower generation, vertical axis hydrokinetic rotors work at low water velocity and are suitable for small-scale hydropower production. Among the vertical axis water turbines, the Darrieus rotors make use for a specific implementation because they are economic and independent to the water direction. Therefore, many investigations have been realized to boost its efficiency. In this work, experimental tests realized in an irrigation canal were performed with a 3D printed Darrieus rotor. With the intention of the performance betterment of the studied rotor, a novel blade shape namely V-shaped blade was tested numerically using the commercial software ANSYS FLUENT 17.0. The maximum value of the power coefficient of the Darrieus rotor reaches 0.17 using twisted blades. However, using V-shaped blades, the highest value of the power coefficient gets at 0.185
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
Numerical Model Parameters Impact on Savonius Wind Rotor Performance
Full text linkGlobal greenhouse gas emissions are mostly caused by the production of energy extracted from fossil fuels sources. Indeed, the use of renewable clean energy has become crucial to supply the world demand while protecting the planet. For many years, there has been a great deal of interest in wind energy because it is a clean, sustainable energy source. Because of its cheaper cost and independence from wind direction, the Savonius vertical axis wind rotor has the advantage of being suitable for certain implementations as an energy converter. Several studies have been carried out to increase its efficiency from this angle. This research work emphasizes on the Savonius wind rotor numerical model performances. The main goal is to explore the impact of setting the numerical model parameters on its aerodynamic and performance characteristics. Ansys Fluent software 17.0 was utilized to perform numerical simulations utilizing the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. The mesh sizing, the turbulence model as well as the time step parameters were investigated. The numerical model validation was realized through published experimental findings available in the literature for an inlet wind velocity of 6 ms-1. Good accordance was obtained. Thus the numerical model with the selected parameters was relevant for further investigations. For a tip speed ratio λ=0.64 it gave a torque and power coefficients equal to 0.328 and 0.2, respectively
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
Experimental and numerical investigation of Zephyr-type wind turbine
No full textThe search for more environmentally friendly energy sources has been prompted by growing environmental concerns. In this regard, wind energy can be an alternative viable source of energy for world electricity demand supply. Despite of their benefits in terms of simplicity of manufacture, independency on wind direction and good starting ability in turbulent flow, Savonius wind turbines as a vertical axis wind energy converter are not recommended for large-scale power generation because of their poor performances. This research emphasizes on the performance improvement of a Zephyr wind rotor (ZWR). Experimental tests were conducted in a wind tunnel for different Reynolds numbers. Maximum power coefficient of 0.074 was recorded for Re = 158,000 corresponding to V∞ = 10 m s−1 at a tip speed ratio of λ = 0.99. Numerical study was carried out with the use of Ansys Fluent 17.0 software through transient 3D simulations investigating the optimization of the ZWR rotor blades and stator vanes with the aim of performance betterment. Maximum power coefficient of 0.168 was found with 8-bladed ZWR with 12 stator vanes. Aerodynamic properties were also improved
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
Performance Improvement of a Drag Hydrokinetic Turbine
Full text linkHydropower is at present in many locations, among all the other possible renewable energy sources, the best one for net cost per unit power. In contrast to traditional installation, based on water storage in artificial basins, free flow river turbines also provide a very low environmental impact due to their negligible effect on solid transport. Among them, kinetic turbines with vertical axis are very inexpensive and have almost zero impact on fish and local fauna. In application to tidal waves and sea waves, where vertically averaged velocities have alternate direction, a Savonius rotor also has the advantage of being productive during the whole time cycle. In this work, the effect of an upstream deflector system mounted upstream of a twisted Savonius rotor inside a channel has been investigated through numerical simulations and experimental tests. Numerical simulations were carried on using the ANSYS FLUENT 17.0 software. Based on this numerical study, it is shown that the proposed deflector system has improved the power coefficient of the Savonius rotor by 14%. The utilization of this new design system is predicted to contribute towards a more efficient use of flows in rivers and channels for electricity production in rural areas
- …
