1,720,984 research outputs found
Self-Ignition of Aviation Fuels in Direct Injection Diesel Engines
No full textThe avio Diesel engine is believed to be an innovative, high efficient and powerful engine system in thr air transport. In this paper, the self-ignition of standard jet-fuels in a Diesel engine-like environment is studied. The jet-fuel ignition plays an important role of the entire combustion process to minimize the weight/power ratio, without compromising the high conversion efficiency and the low production of pollutants opf modern Diesel engines. The Shell auto-ignition model is used to simulate the Jet-A and JP-8 fuels auto-ignition. Ad-hoc model kinetic parameters are proposed. The results are compared with those available in the literature to show the accuracy of the proposed model constants
RANSEs Simulation of the Flow past a Marine Propeller under Design and Off-design Conditions
No full textIn the present work the results of a preliminary computational fluid dynamics (CFD) simulation of the flow past a marine propeller are presented. The principal aim of the study is to verify the ability of a CFD method, solving the Reynolds-Averaged Navier-Stokes Equations (RANSEs), to predict the performances of a marine propeller. The complexity in the mesh generation is one of the main obstacles for CFD. Following an hybrid mesh generation approach, prisms have been generated in the boundary layer, where viscous phenomena are dominant, and tetrahedra in the remaining regions. A parallel RANS solver has been used, employing a cell-centered, finite-volume method that allows the use of computational cells of arbitrary polyhedral shape. Boundary conditions were given to simulate the flow past a rotating propeller in open water conditions. The equations have been written in a moving reference frame fixed on the propeller blades. The steady-rotating reference frame source terms, i.e., the centrifugal and Coriolis force terms, therefore, are added to the RANS equations derived in the inertial frame. The k-w model has been employed for turbulence closure. Different values of advance ratios are considered, at design and off-design conditions. Computational results have been obtained for all the four-quadrant operational conditions: forward, backing, crashback and crashahead, considering also non-positif values for the advance ratio J. The thrust and torque coefficients, k_T and k_Q, have been selected as global quantities and compared with available experimental data. Pressure and velocity distributions and turbulent quantities were also used to analyze the computed flow field. The results show a good qualitative agreement with the experimental data. Important issues need to be addressed like an extensively improvement in the mesh generation techniques and in turbulence modeling
Simulazione numerica bidimensionale di turbine marine ad asse verticale
No full textIn questo lavoro si è sviluppato un modello di previsione delle prestazioni di una turbina marina ad asse verticale seguendo un approccio di tipo teorico-numerico. E` stato utilizzato, come strumento di analisi, un codice di calcolo che risolve le equazioni di Navier-Stokes non stazionarie per campi di moto bidimensionali incomprimibili, adottando un metodo ai volumi finiti. Si è dapprima verificata l’esatta impostazione del metodo utilizzato per confronto con varie configurazioni di flusso per le quali sono reperibili in letteratura dati numerici e sperimentali. Successivamente si è utilizzato il codice, opportunamente modificato, per predire le caratteristiche di funzionamento di un modello semplice di turbina ad asse verticale, del tipo Darrieus, costituito da un’unica pala avente un profilo alare di tipo simmetrico con corda rettilinea, appartenente alla serie NACA. L’analisi delle prestazioni di questo modello semplificato di turbina è stata effettuata sia mediante visualizzazioni del campo di moto che si instaura intorno alla pala, sia calcolando l’evoluzione temporale della potenza disponibile all’asse. E’ stata condotta un’analisi parametrica al variare del numero di Reynolds e del rapporto l tra la velocità periferica del rotore e la velocità della corrente indisturbata. Per ciascuna coppia di valori di questi due parametri si è analizzato l’andamento dei coefficienti aerodinamici e del coefficiente di coppia al variare della posizione assunta dalla pala durante la rotazione, ottenendo così l’andamento del coefficiente di potenza in funzione del parametro lambda. Sono stati infine eseguiti confronti con risultati sperimentali disponibili in letteratura mettendo in evidenza l’attendibilità del modello numerico
“Pecunia adsidua permutatione quodammodo extinguitur”. Spunti per una definizione del denaro nel dibattito su usura e povertà francescana
No full textIl saggio vuole mostrare come il dibattito sulla povertà francescana abbia potuto svolgere un ruolo nel passaggio da una concezione "metallistica" della moneta ad un approccio più astratto, non senza possibili ricadute sulla teoria medievale dell'usura. Il volume è a cura di R. Lambertini e L. Sile
Coordinate del mondo moderno: i rapporti tra Inquisizione romana e Propaganda Fide
No full textThe Roman Inquisition and Propaganda Fide contributed with their close relation to determining the early modern world. The Holy Office was always focused not to allow other institutions to discipline Catholic orthodoxy, morality or to judge the reserved cases. Propaganda increasingly centralised control of the missions in the hands of the pontiff, stimulating the formation of the indigenous clergy. Despite this, the two institutions clashed fiercely. The paper aims to highlight some of the main theological, curial, and diplomatic contrasts through which the papal Holy Office imposed itself and its power on the Propaganda Fide, almost always succeeding in this goal. Only the reforms of the 20th century would give Propaganda a broader sphere of action in a now truly global Church
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
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