1,721,001 research outputs found
Autoignition characteristics of diesel sprays under different injection conditions
No full textAn experimental study analyzing the complex relationship between external thermo fluid dynamic parameters and the ignition of diesel sprays, as well as flame propagation, is presented. The experiments were performed in a high-pressure, high-temperature system simulating the top dead center conditions in the combustion chamber of a diesel engine. The only simplification with respect to real diesel engines is relative to the aerodynamic pattern. In fact, in this case, the air flux is almost quiescent and does not influence significantly the spray evolution or the combustion behavior. The influences of two very different injection regimes on the autoignition characteristics of diesel sprays were investigated using imaging techniques. In order to perform this analysis, a careful choice of injection conditions, obtained with two different types of injection apparatus, was necessary. The spray evolution at both low and high temperatures (at the same air density), the temporal and spatial distributions of the ignition points, and the flame growth velocity were measured for the two cases. Analysis of the results revealed the specular behavior of the ignition spatial distributions ill the two cases. A first attempt to correlate these different behaviors with the spray-flame interaction is presented, and its implications are discussed
Bending and break-up of a liquid jet in a high pressure airflow
No full textThe aim of this paper is to investigate the characteristics of the atomization process of a liquid jet injected into a high-pressure air cross-flow, i.e. in condition similar to that occurring in the inlet duct of a LPP gas-turbine burner. The influences of controlling parameters such as air velocity, liquid velocity and diameter of the nozzle are considered. The main features of the spray morphology were determined by means of a tomographic visualization technique and the general evolution of the spray in some typical cases is presented in the paper. It is shown as the jet evolution is significantly influenced by the onset of a stripping atomization mechanism marked by the peculiar morphology of the spray cross-section. This is also evident from the observation of the jet trajectories determined by using a shadowgraphic technique. The different behavior of the atomization process induced by the stripping mechanism led to a bi-stable evolution of jet trajectory in dependence of the prevalence of the liquid or air velocities effects. This feature can be hardly modeled by the interpolating function proposed in the literature. As a consequence, a stronger effort to gain a deeper understanding of the fluid dynamic, involved in the jet break-up in presence of an air cross-flow, is still required in order to build-up a more realistic model of the jet trajectory evolution. (C) 2003 Published by Elsevier Science Inc
Le iscrizioni pavimentali della Basilica tra il 1600 e il 1823
No full textNel 1823, anno del fatidico incendio, il pavimento della basilica di San Paolo era formato da migliaia di lastre marmoree, intere e frammentarie, disposte con una trama irregolare. La moltitudine sparsa di iscrizioni cristiane e pagane, latine e greche, e di pezzi scultorei, appartenenti alle prime fasi della basilica e al sottostante sepolcreto pagano, mostravano il lato più caratteristico della storia dell'edificio. Dallo smantellamento del lastricato, realizzato in parte già nel corso dei secoli, a partire da Sisto V, e poi completamente, in seguito all’incendio, traggono origine le due collezioni museali del chiostro e del monastero (Lapidario Paoliano).
All'epoca di Innocenzo X (1644-1655), Cornelio Margarini esegue la prima ricognizione sistematica delle iscrizioni impiegate nel pavimento, rilevandone il testo e la posizione; il suo testo, insieme alla silloge del Nicolai (1815) costituisce una fonte essenziale per la conoscenza del patrimonio epigrafico paolino, dal momento che molte delle lastre allora rilevate sono oggi perdute. L’articolo riferisce poi delle esplorazioni archeologiche condotte di recente sotto la navata laterale destra, che hanno portato al rinvenimento di alcuni frammenti epigrafici, pertinenti al pavimento, collocati nella posizione in cui furono indicati dal Margarini.
La sottoscritta si sofferma in particolare sui primi risultati di una ricerca relativa al rinvenimento, su alcune lastre pavimentali, di incisioni che farebbero pensare alla presenza, nel pavimento dell’antica basilica, del disegno della cupola di San Pietro in Vaticano; notizia riportata da diverse fonti ma mai confermata né approfondita da altri. Finora, infatti, le notizie d'archivio, note soprattutto agli studiosi della cupola vaticana, potevano, in mancanza di riscontri diretti, considerarsi alla stregua di un'interessante notazione sulle tecniche di cantiere o, al più, di un aneddoto.
Le indagini dirette sulle lastre, condotte con l’uso di apparecchiature laser scanner, hanno lo scopo di ricostruire, tramite un rilievo tridimensionale di altissima precisione, la curvatura dei diversi tratti di incisione, per tentare poi una ricollocazione virtuale delle lastre, basata anche sulle indicazioni fornite dalla documentazione archivistica
Influence of inverter control logics on energetic performances of PV modules – inverter systems
No full textSloshing phenomenon analysis in liquid fuels storage tanks subject to seismic event
No full textIntent of the work is to evaluate the behaviour of liquid fuels contained in storage tanks, when subject to an earthquake.
Particular attention has been addressed to fluid motion, defined sloshing, and to the forces which it exercises on tank
structure. The analysis was performed with the help of a CFD commercial software, properly integrated with appropriate
subroutines. The tank analysed is cylindrical (diameter = 10 m, height = 11m).
The simulations were made for different filling levels, 25, 50 and 75%, subjecting the tank to 7 different acceleration inputs.
Results are presented in form of temporal variation of pressure, movement of fluid gravity centre, forces and moments on the
structure
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