1,720,994 research outputs found
4D Printing: an emerging technology in Manufacturing?
No full textThe paper highlights the possible technological evolution in the Lean manufacturing that concerns 4D Printing. To date there are not case studies of 4D printing application able to demonstrate the effective use of 4D Printing, and its results on the production cycles. The purpose of this article is to review the state of the art of the developments in four dimensional (4D) Printing, through a literature review, in order to define the 4D Printing characteristics, to examine its perspectives for the future application in manufacturing and to identify the potential benefits and manufacturing advantages
Cloud Manufacturing: Innovation in Production
No full textIn production, combining several emerged technologies such as cloud computing, service-oriented technologies, and the Internet of Things, a new manufacturing system is introduced. Cloud Manufacturing is a form of decentralized and networked manufacturing paradigm, and it could be represent the evolution of other relevant manufacturing systems such as web-manufacturing and agent-based manufacturing. The research community debates on several aspects of CM such as definitions, key characteristics, requirements, operational processes. One question, in particular, has often been raised among the researchers: if cloud manufacturing can be considered as an innovation in manufacturing. Based on the state of the art of the academic research about the definition of CM, the requirements that an ideal CM system should satisfy, and the discussion of its characteristics, the concept of CM is discussed in this paper, including strategic aspects and the key technologies, with specific reference to Additive Manufacturing
La propensione all'acquisto dei prodotti "Made in Italy": analisi del comportamento dei consumatori tra qualità percepita e disponibilità a pagare. Un'investigazione empirica
Full text linkIl presente contributo ha l’obiettivo di analizzare l’atteggiamento del consumatore nei confronti dei prodotti “Made in Italy”, in particolare allo scopo di individuarne gli attributi associati e i sistemi valoriali che possono influenzare l’acquisto. Le domande di ricerca sono essenzialmente le seguenti: 1) Esiste una riconoscibilità del “Made in Italy” in termini di caratterizzazione qualitativa dei prodotti? Se si, 2) Esiste una disponibilità pagare, in termini quantitativi, un “premium price” per tali prodotti? Si offre una disamina attraverso due metodologie. Da un punto di vista teorico, viene presentata la principale letteratura sul tema cercando di individuare i filoni scientifici di riferimento come il Country of Origin, il Country Image e la Brand Image, che si inseriscono in un contesto più ampio riguardante la Willingness to Pay. Dal punto di vista empirico, si è investigato, mediante l’uso di un questionario, sull’esistenza e sulla tipologia di una relazione tra la percezione della qualità la disponibilità a pagare un prodotto “Made in Italy”. Presentando gli esiti della ricerca condotta, i principali risultati mostrano che il “Made in Italy” è ben fissato come categoria concettuale nella mente dei consumatori. C’è un significativo “premium price” riconosciuto dagli stessi verso i prodotti “Made in Italy” per i settori analizzati (alimentare, abbigliamento e arredamento). Il “premium price” non è omogeneamente individuato per i vari settori merceologici analizzati, anche se per tutti i settori il valore comunemente riscontrato è relativo al 10%-30%
Characterization of the behavior of cryogenic propellants in tanks
Full text linkWith the introduction of cryogenic propellant combinations for space engines, there has been an
increasing interest in the study of the behavior of the propellant in the tanks in which it is stored.
This study can be carried out in two ways. The first approach involves both the dynamic behavior
of the propellant, i.e. the sloshing analysis, and the thermo-fluid-dynamics behavior, which are
analyzed as coupled phenomena. Conversely, in the second approach, the two phenomena are
studied separately. In this thesis, the second approach has been used, and only the thermo-fluiddynamics
characterization of the behavior of cryogenic propellant in tanks has been carried out, since
a consolidated reduced order activity on the sloshing analysis is already present in the literature.
Cryogenic propellants, having a very low boiling point, are subject to phase transitions even
when exposed to very low heat leaks. As a result, the pressure raises inside a closed non-venting
tank. Moreover, the tanks, especially those belonging to the upper stages of space launchers, are
subjected to time-varying heat leaks and gravity levels during their operating life. The thermo-fluiddynamics
characterization mainly aims at estimating the evolutions of tank pressure, of the local
fluid temperatures, of the phase change rate, and of the propellant location (in the case of reduced
gravity). All these analyses, are necessary in order to guarantee the reliability and safety of a tank
operation (feed turbopumps with propellant at appropriate temperature and pressure conditions,
guarantee that only liquid drains from the tank outlet, ensure that only vapor comes out of the
venting valve, etc.).
Due to the cost and complexity associated with the experiments, numerical tools of various
levels of complexity have been implemented over the years to carry out the thermo-fluid-dynamics
characterization. The first approach is characterized by the use of reduced order models. The
latter allow quick estimates of the main observables, and, therefore, represent an engineering tool
necessary in the case when a large number of parametric analyses has to be carried out, as in an
industrial design process. The second approach involves Computational Fluid Dynamics (CFD)
simulations. These last allow to perform more accurate analyses than the previous approach, and
to study the complex physical phenomena at play. However, the drawback of CFD simulations is
the elevated computational cost with respect to the reduced order models.
The aim of this study is twofold. On the one hand, a suitable zero-dimensional model has been
developed, implemented in Matlab, and successfully verified through the comparison with the results
of a one-dimensional code developed by NASA (see Chap. 2). Later, it has been used to simulate
two tank characteristic operating conditions, for which experimental data were also available. A
ground-based self-pressurization experiment in a small-scale liquid N2 tank (see Chap. 4) and a
ground-based active-pressurization experiment in a different small-scale liquid N2 tank (see Chap.
5). On the other hand, the aim of the study has been the development of a state-of-the-art CFD
methodology (see Chap. 3), capable of estimating the main thermo-fluid-dynamics observables,
and to study the main physical phenomena at play inside tanks of various species of cryogenic
propellant, and characterized by different operating conditions. The proposed methodology has
been successfully validated through the comparison with the experimental data of three benchmark
test cases, characterized by different propellants, geometries, and operating conditions. This has
been done in order to develop a computational tool which guarantees reliability during most of the
operating life of the tank. Moreover, for the various validation test cases, different physical and
numerical models and parameters have been tested, in order to find the ones which allow the best
reproduction of a particular operating condition, as well as the optimal parameters in terms of the
trade-off between accuracy and computational time. The three validation test cases which have
been simulated are:
• A ground-based liquid N2 self-pressurization test case, inside a small-scale tank (see Chap.
4).
• A ground-based liquid N2 active-pressurization test case, inside a small-scale tank (see Chap.
5).
• A self-pressurization test case carried out in the liquid H2 tank of the second stage of the
Saturn IB AS-203 vehicle, while it was into circular low Earth orbit (see Chap. 6).
Then, the validated CFD methodology has been used to carry out a parametric study on the gravity
level. In particular, four gravity levels, from normal gravity (gE = 9.81 m/s2) until the reduced
gravity of 10−3gE, have been considered. This study has been performed using the same geometry,
fluid, and operating conditions of the first validation test case. The parametric study has allowed
to see the effect of the gravity level on the pressurization behavior, phase change, and liquid-ullage
interface shape.
Finally, the developed, and repeatedly validated zero-dimensional model and CFD methodology
have demonstrated to allow to perform, with a different level of detail, the thermo-fluid-dynamics
characterization of the behavior of cryogenic propellant, under most of the operating conditions of
interest for tank design. Nevertheless, the operating conditions considered in the present thesis do
not involve the case of fluid with sloshing. In order to carry out a more comprehensive study of the
actual behaviour of cryogenic propellant in tanks, the sloshing phenomenon should be included in
future work. Indeed, sloshing happens very often in cryogenic propellant tanks and, although being
a mainly dynamic in nature process, it has a strong influence on the propellant thermal physical
phenomena
Numerical tank self-pressurization analyses in reduced gravity conditions
No full textIn this study, a suitable numerical methodology to study the self-pressurization phenomenon inside a cryogenic tank, in a reduced gravity environment is proposed. This methodology is validated with the results of a benchmark self-pressurization experiment, carried out in the liquid hydrogen tank of the second stage of the Saturn IB AS-203 vehicle. The time-varying acceleration and heat flux due to solar radiation to which the tank was exposed during the experiment, have been modeled in our analysis. Finally, the numerical results show that the proposed methodology allows to reproduce the experimental data with a reasonably good accuracy
Setup of a numerical methodology for the study of active-pressurization of cryogenic tanks
No full textIn this paper, a numerical methodology to study the active-pressurization inside cryogenic tanks is proposed
and validated with the results of an active-pressurization experiment in normal gravity, inside a
liquid nitrogen (N2) tank. The tank is modeled as 2D axisymmetric, a fluid-wall conjugate heat transfer
model is used, and the two-phase fluid interface is tracked with the Volume-of-Fluid (VOF) method. The
results show that the experimental data are accurately reproduced with the SST k − ω with low-Re corrections
turbulence model, and that the modeling of the shutdown of pressurant gas injection requires some
attention from a numerical standpoint
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
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
Education & Technology for a Sustainable Future. The case study of Solar Decathlon
No full textSapienza University of Rome participates in Solar Decathlon Middle East 2018 International Competition, aiming to design and realize the best sustainable and energy-efficient housing prototype on a real scale. The purpose of the project is to create a Smart Solar House that can guarantee maximum efficiency and effectiveness in the use of natural resources and provide an attractive, accessible, comfortable and healthy environment. The aim of the paper is to analyze the contest from Educational standpoint, highlighting the aspects of Smart Systems and Smart People. Two phases methodologically joined between them are studied. In particular, 1) from a technology point of view the high-efficiency plant solutions, integrating renewable energy sources and advanced systems of building automation are deepened; And 2) from a socio-cultural standpoint the education and the direct involvement of users who will be able to consciously manage energy consumption and levels of comfort through the use of home automation systems are analyzed. The paper is divided into four sections. After the introduction, the second section offers a literature review of Smart House placed in a broader context on Education by users that concerns the use of enabling technologies, the third section explains the case study of Solar Decathlon Middle East, in the fourth section future remarks research directions are addressed
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