3,648 research outputs found
Aerothermodynamic modelling of meteor entry flows in the rarefied regime
Get PDFDue to their small size and tremendous speeds, meteoroids often burn up at high altitudes, above 80 km, where the atmosphere is rarefied. Ground radio stations are able to detect the free electrons concentration in the meteoroid wake, which is produced by hyperthermal collisions of the ablated species with the free-stream. The interpretation of radio data, however, currently relies on phenomenological methods, derived under the assumption of free molecular flow, hence, poorly accounts for the dynamics of the vapour, chemistry, and diffusion in the meteor trail. In this work, we aim to provide a detailed description of the flowfield around a meteoroid by means of Direct Simulation Monte Carlo and to obtain the evolution of the free electrons in the meteor wake via an extended trail simulation. An evaporation boundary condition is developed in the framework of an open source DSMC software. The material is assumed to be composed by a mixture of metal oxides which are typically present in ordinary chondritic meteorites. The transport properties of the ablated vapour are computed following the Chapman-Enskog theory and the DSMC phenomenological parameters are retrieved by fitting the collision integrals over a wide range of temperatures. As a last step, chemical and diffusion processes in the trail are computed. Starting from the baseline DSMC solution, our approach marches in time along the precomputed streamlines, calculating chemistry and radial diffusion for metals and free electrons. As study case, the flow around a 1 mm evaporating meteoroid is analysed at different altitudes. A high level of thermal nonequilibrium is appreciated in the head of the meteor, whereas in the trail, after a few diameters, the flow equi-librates. At lower densities, the vapour can travel upstream without interacting much with the incoming jet. On the other hand, at lower altitudes, re-condensation plays a significant role in the stagnation region. Finally, a trail, several meters long and formed by metallic species, generates behind the body. Ionization of sodium turns out to be the dominant process in the production of free electrons, whereas radial diffusion seems to prevail over recombination as depletion mechanism
Aerothermodynamic modelling of meteor entry flows
Get PDFDue to their small size and tremendous speeds, meteoroids often burn up at high altitudes above 80 km, where the atmosphere is rarefied. Ground radio stations allow us to detect the concentration of electrons in the meteoroid trail, which are produced by hyperthermal collisions of ablated species with the freestream. The interpretation of these data currently relies on phenomenological methods, derived under the assumption of free molecular flow, that poorly accounts for the detailed chemistry, diffusion in the vapour phase, and rarefied gas effects. In this work, we employ the direct simulation Monte Carlo (DSMC) method to analyse the detailed flowfield structure in the surroundings of a 1 mm meteoroid at different conditions, spanning a broad spectrum of Knudsen and Mach numbers, and we extract resulting ionization efficiencies. For this purpose, we couple the DSMC method with a kinetic boundary condition which models evaporation and condensation processes in a silicate material. Transport properties of the ablated vapour are computed following the Chapman-Enskog theory starting from Lennard-Jones potentials. Semi-empirical inelastic cross-sections for heavy- and electron-impact ionization of metals are computed analytically to obtain steric factors. The ionization of sodium is dominant in the production of free electrons, and hyperthermal air-vapour collisions play the most important role in this process. The ionization of air, classically disregarded, contributes to the electron production as significantly as ionization of magnesium and iron. Finally, we propose that DSMC could be employed as a numerical experiment providing ionization coefficients to be used in synthetic models
Milano consolato nell' elettione a questo arciuescouado, e promotione alla sagra porpora dell' eminentissimo Federico Visconti : colla sua solennissima entrata seguita a' 11. genaro 1682 e fontioni antecedenti /
No full textFrontispiece coat of arms of Milan, engraved by Federico Agnelli.Signatures: pi⁴ A-G⁴ H⁴(-H4).Mode of access: Internet.Binding: limp vellum. Author & title written on spine
Development of a melting model for meteors
Get PDFMeteor phenomenon is a frequent event happening on planet Earth. Due to the high entry velocities of these objects the surface of the material undergoes extreme heat loads. Since the material is mainly composed by several oxides, eventually, the surface temperature will overcome the melting point. In this study we propose a melting model, in order to understand the material behavior, coupled with a flow solver. A detailed study of the flow around the stagnation streamline is also presented
Studio di un modello di vaglio rotante per la selezione dei rifiuti
No full textLAUREA MAGISTRALEQuesta Tesi riguarda la modellazione di vagli a tamburo rotante utilizzati per il trattamento di Rifiuti Solidi Urbani (RSU). La vagliatura è uno dei processi fondamentali che compongono gli impianti di Trattamento Meccanico-Biologico (TMB) dei rifiuti. Il lavoro svolto ha analizzato nel dettaglio due modelli di vaglio a tamburo presenti in letteratura, quello sviluppato da Stessel e Kranc e quello sviluppato da Mellmann. Mentre il primo si riferisce effettivamente a vagli per il trattamento dei rifiuti, il secondo riguarda in generale la dinamica delle particelle all’interno di cilindri rotanti (con particolare riferimento ai forni a tamburo) ed è quindi stato adattato. Entrambi i modelli sono stati analizzati mediante strumenti Excel e Matlab, evidenziando diverse criticità. Per questa ragione si è indagato un ulteriore approccio modellistico basato sulla dinamica elementare delle singole particelle e chiamato, in letteratura, DEM – Discrete Element Method. Sulla base del lavoro di Luding, è stata delineata la struttura base di un codice DEM per la simulazione della vagliatura dei rifiuti con vagli a tamburo rotante.This Thesis focuses on the modelling of rotating screens (trommels) for the processing of Municipal Solid Waste (MSW). Waste screening is one of the fundamental processes in Mechanical-Biological Treatment (MBT) plants. The work carried out analysed in detail two trommel models found in the literature: the one developed by Stessel and Kranc, and the one developed by Mellmann. Whereas the former actually refers to trommels for waste processing, the latter generally concerns particle dynamics inside rotating cylinders (with a special focus on rotary kilns) and, thus, it has been adapted. Both models have been evaluated by means of Excel and Matlab tools and highlighting several critical aspects. For this reason, a further modelling approach has been investigated. The elemental dynamics of single particles has been considered, adopting the Discrete Element Method (DEM) approach. On the basis of the work carried out by Luding, the basic framework of a DEM code has been lied down, for the simulation of waste screen through trommels
»It contained harbours that pleased me like sonnets«. Kleine Poetik der diegetischen Karte
No full textIn this article, Federico Italiano explores the relationship between literature and cartography. Beginning with Stevenson’s Treasure Island, the author frames the topic through a general theoretical lens on the spatial dimension of literary texts. He then focuses on a specific phenomenon of literary "carticity"—the diegetic presence of the map, that is, the map as an integral element of the narrative structure. Among others, Italiano examines the works of Houellebecq and Cormac McCarthy
Laser-Based Active Debris Removal: A Satellite Constellation Approach for Mitigating Small-Sized Space Debris in Low Earth Orbit
Get PDFThe growing issue of space debris poses a critical challenge as Earth’s orbits become increasingly con-
gested due to expanding space activities. Low Earth Orbit (LEO) is particularly affected, with an estimated
900 000 debris fragments ranging from 1 to 10 cm in size. These objects are large enough to penetrate space-
craft shielding yet too small to be effectively tracked, creating a severe and unpredictable collision risk.
Existing mitigation strategies, such as end-of-life de-orbiting and graveyard orbit transfers, have proven
insufficient in preventing debris accumulation. Consequently, Active Debris Removal (ADR) has emerged
as a key research focus. Among proposed ADR techniques, laser ablation presents a promising solution,
enabling remote, contactless trajectory alteration. This research investigates the feasibility of a laser-based
ADR mission utilizing a constellation of satellites dedicated to debris detection and removal. Each satellite
is designed with an advanced payload capable of autonomously identifying debris, assessing its trajectory,
and engaging targets using a high-power pulsed laser system. The laser operates in the nanosecond pulse
regime, with beam propagation characteristics analyzed for an effective operational range of approximately
100 km. A detailed study of laser-material interactions is conducted using a surface energy balance ap-
proach, complemented by a 3D heat conduction model that simulates the thermal response of debris under
realistic conditions. This allows for the evaluation of the ablation area, the forces exerted on the debris
surface, and the efficiency of the laser-induced momentum transfer. Based on the outcomes of this study,
a dedicated satellite constellation is proposed, operating within an altitude range of 250 to 1 000 km and
an inclination range of 60 to 105 degrees. The final architecture consists of approximately 20 satellites
strategically positioned to maximize debris removal efficiency. Simulation results indicate that this system
could successfully remove around 25% of small-sized debris within a 25-year timeframe, aligning with the
guidelines set by the Inter-Agency Space Debris Coordination Committee (IADC)
Portrait of the Author in (Him/Her)self
No full textA fragment of a philosophical essay by Jean-Luc Nancy and Federico Ferrari titled Iconographie dell’auteur (Paris, 2005), published for the first time in Polish, that addresses the problem of a relationship between the image of the author and his/her work
Aneddoti e ricette a corte di Federico II nel XXI secolo : il buon cibo e il buon bere nel più antico Ateneo pubblico al mondo
Get PDF[Italiano]: Questo volume rappresenta la finalizzazione di una iniziativa nata, condivisa ed interamente realizzata all'interno del gruppo social dei "Prof in cucina e in Cantina", che ha inteso raccogliere ricette e descrizioni aneddotiche di singoli Autori, appartenenti ai ruoli del personale docente e tecnico-amministrativo-bibliotecario dell'Ateneo federiciano, il più antico Ateneo pubblico al mondo. Aneddoti e ricette forniscono spaccati di vita quotidiana e ricostruzioni di eventi che hanno accompagnato gli Autori nei diversi percorsi formativi, sociali e lavorativi, e che non escludono riferimenti al recente periodo emergenziale della pandemia COVID-19. Ad introdurre il Volume è un menù federiciano, con una proposta di 3 pietanze che attualizzano ricette ed abitubini alimentari dell'epoca, e che hanno come riferimento il Liber de coquina, edito a corte di Federico II. Gli 8 Capitoli del volume raggruppano ricette e aneddoti per categorie, e ciascuno di essi è poi preceduto da un breve inserto con ulteriori riferimenti storici all'alimentazione a Corte di Federico II. Così, atmosfere vecchie e nuove, accompagnate dal sentore di aromi e da suggestioni ispirate al vissuto di ciascun Autore, si fondono per offrire a Lettrici e Lettori frammenti di quotidianità vissuti oggi a corte di Federico II, nel XXI secolo./[English]: The Volume represents the endpoint of a recent initiative, which was conceived, shared and fully realized within the social group of the "Prof in Cucina e in Cantina". Here, the several Authors, represented by the teaching and the technical/administrative/librarian staff of the Federico II University in Naples, the oldest public University in the world, propose recipes and anecdotal descriptions of their educational, social and work-related paths, including some episodes from the recent COVID-19 pandemic. A menu inspired to Frederick II introduces the book, with 3 recipes inspired to the Liber de coquina, a cooking manual compiled at the Emperor's court. Each of the following 8 thematic chapters of the book is also anticipated by a brief insert reporting historical reconstructions of the alimentary habits at the court of Frederick II. Thus, old and new atmospheres, accompanied by the scent of aromas and suggestions inspired by the experience of each Author, come together to offer Readers fragments of everyday life at the court of Frederick II, in the 21st century
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