1,720,953 research outputs found
Two-dimensional URANS modeling of an H-type darrieus wind turbine
No full textLAUREA MAGISTRALERecenti sviluppi dell’energia eolica hanno portato a una rivalutazione delle turbine eoliche ad asse verticale per la microgenerazione e nei parchi eolici off-shore. Nel tentativo di aumentare l’efficienza e la competitività dei prototipi esistenti, il presente lavoro di tesi si prefigge lo scopo di modellizzare la complessa aerodinamica di un rotore ad H tramite l’impiego della CFD, validando i risultati numerici mediante un confronto con dati sperimentali ricavati in precedenza.
Il benchmark dell’analisi consiste in una campagna sperimentale condotta all’interno della galleria del vento del Politecnico di Milano nella configurazione a getto libero e a bassa turbolenza (<1%). Il rotore ad H è equipaggiato con tre pale NACA 0021 verticali ed è caratterizzato da un’area spazzata di 1,5 m2. I valori della coppia e della potenza sono ricavati rispettivamente con un misuratore di coppia montato sull’albero e un encoder. La velocità e l’intensità di turbolenza della scia della turbina sono calcolati impiegando tecniche di anemometria a filo caldo su due piani a valle della turbina. La velocità del flusso è compresa tra 6 e 16 m/s e permette di esaminare le più rilevanti condizioni di funzionamento, mantenendo costante la velocità angolare a 400 rpm.
Lo studio CFD è realizzato tramite il codice commerciale ANSYS® Fluent adottando un approccio URANS bidimensionale. In particolare, la prestazione della turbina in termini di potenza, scia generata e stallo dinamico è valutata usando i modelli di turbolenza SST k−omega e Spalart-Allmaras. Il modello numerico è validato analizzando l’influenza dell’estensione del dominio e del passo temporale sui fenomeni aerodinamici. Successivamente si confrontano le curve di CL e CD con le curve sperimentali tratte dalla letteratura. Vengono esaminate le condizioni di funzionamento più rilevanti con tre rapporti di velocità di punta: 3,3 (basso carico), 2,4 (Cp ottimale) e 1,5 (alto carico). Entrambi i modelli vengono usati in configurazione standard e con la correzione di curvatura. Infine, risultati numerici vengono discussi e confrontati con i dati sperimentali.
I migliori risultati in termini di generazione di coppia e predizione della scia vorticosa vengono trovati per lambda = 2,4, grazie alla limitata nucleazione dello
stallo dinamico e al regime di flusso pienamente turbolente attorno alle pale. Per lambda = 1,5 i risultati sono solo moderatamente soddisfacenti, in quanto vengono trascurati forti vortici d’estremità. Per lambda = 3,3 i modelli URANS risultano inadeguati, a causa dello strato limite parzialmente laminare e un eccessivo rateo di dissipazione dell’energia cinetica turbolenta.Recent developments in wind energy have led to a reconsideration of vertical axis wind turbines for microgeneration and off-shore wind farms. Within the context of the need to increase the efficiency and competitiveness of the existing prototypes, this thesis aims at simulating the complex aerodynamics of a real-scale H-rotor by means of CFD modeling, and by assessing the numerical results by virtue of a detailed comparison with existing experimental data.
The benchmark for the analysis consists in an experimental campaign carried out at the Politecnico di Milano wind tunnel in open chamber configuration and low turbulence (<1%). The H-rotor is equipped with three straight NACA 0021 blades and has a swept area of 1,5 m2. Torque and power are measured with a torque-meter mounted on the pole and an encoder, respectively. Velocity and turbulence intensity of the turbine’s wake are evaluated using hot-wire anemometry on two planes located downstream of the turbine. Wind speeds ranging from 6 to 16 m/s have been tested to cover all relevant operating conditions, with a constant angular velocity of 400 rpm.
The CFD investigation is carried out with the commercial software tool ANSYS® Fluent adopting a two-dimensional URANS approach. In particular, the turbine’s performance in terms of power, generated wake and dynamic stall are evaluated using the SST k − omega and the Spalart Allmaras turbulence models. The numerical model is validated through an analysis of the influence of the domain extension and time-step on the aerodynamic phenomena. CL and CD curves are subsequently compared to experimental data found in literature. Tip speed ratios of 3,3, 2,4 and 1,5 representing high load, optimal Cp and low load, respectively, are tested. Both models are used in standard form and with curvature correction. Finally, the numerical results are discussed and compared to the experimental data.
The best results in terms of torque generation and wake prediction are found at lambda = 2,4, thanks to the limited onset of dynamic stall and a fully turbulent
flow condition around the blades. At lambda = 1, 5 only moderate agreement with the experimental data is found, because strong tip vortexes are neglected. At
lambda = 3,3 the URANS models perform the poorest, due to the partially laminar flow in the boundary layer and an excessive turbulence dissipation rate
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
