1,721,089 research outputs found
SCHEMATIC DESIGN. TECNICHE ED ESEMPI DI COMUNICAZIONE DEL PROGETTO
No full textLo schematic design, prassi progettuale molto ben rodata nei paesi anglosassoni, e che in Italia chiamiamo progettazione schematica, è la procedura di descrizione attraverso uno schizzo, o uno schema accuratamente rielaborato, e il relativo commento, di fasi di progetto o di dettaglio che richiedono un'approvazione, una discussione o una verifica. Si tratta di un momento attivo del processo decisionale, che precede quello esecutivo vero e proprio. Il presente volume si compone di una prima parte che tratta il tema dello schematic design dai punti di vista teorico e applicativo, con un taglio che mira a trasferire, quanto più concretamente possibile, utili indirizzi pratico-operativi. Uno degli scopi del libro è infatti di illustrare un buon numero di "trucchi del mestiere", con l'auspicio che questi vengano "copiati", non nel merito specifico ma nello stile rappresentativo, ovvero come prassi comunicativa. La seconda parte del volume è invece incentrata nella presentazione di 100 casi concreti di schematic design organizzati secondo 6 classi di rappresentazione, e attinti da vari progetti di autori noti a livello internazionale. Ogni caso viene affiancato da un commento tecnico relativo tanto all'oggetto mostrato quanto alla tecnica di rappresentazione adottata. L'intento è dunque quello di catturare il "transitorio" di un progetto, analizzarne le fasi non viste, abbandonare la superficie per scendere in profondità, scandagliando lo stesso mestiere di progettista con il gusto (didattico, ma anche professionale) di capire come un'adeguata comunicazione agevoli molto i processi decisionali e creativi, e spesso si traduca direttamente in ottimizzazione economica. In definitiva, il metodo che questo volume presenta permette di accedere in modo consapevole al nostro technical inscape di progettisti, al paesaggio interiore del nostro bagaglio formativo e organizzativo, e di proporre una visione del progetto chiara e ricca di valori costruttivi e comunicativi
Numerical and experimental methods for viscoelastic circular contacts in dry and lubricated conditions
Full text linkThe present thesis is focused on the development of a Boundary Element formulation
to assess two-dimensional steady-state circular contact problems. In particular, the
methodology paves over an ad-hoc defined steady-state viscoelastic Green’s function,
which takes into account the circular hallmark of the contact domain, typical, for example,
of a mechanical pin joint. Crucially, it is able to manage any real viscoelastic
material, characterized by a continuum spectrum of relaxation times. The contact
problem can be easily formulated in the form of a spatial convolution product between
surface stresses and displacement, which blazes the trail to solving contact problems of
a countless number of engineering-relevant systems, where multiple contacts occur, such
as viscoelastic rolling element bearing. Incidentally, to correctly formulate the contact
problem, the definition of the spatial Green’s tensor is crucial. Specifically, the entries
of such tensor, namely the radial and tangential displacements associated to concentrated
radial and tangential unit forces, are determined via a complex variable method.
Conversely to the usual method employing the Airy’s stress function, the complex variable
method allows, through the definition of appropriate complex potentials, a modus
operandi which does not entail the solution to fresh differential equations whenever the
coordinates are changed.
Once the viscoelastic Green’s function is derived, the conformal contact problem of
a rigid pin in contact with a deformable space with a cylindrical hole is investigated. At
first, the methodology is validated against the analytical solution provided by A. Persson
for a purely elastic case; then, the case of a linearly viscoelastic space is analyzed: as
expected in a viscoelastic contact system, at the leading edge, the pressure distribution
peaks, whilst the displacements are larger at the trailing edge, due to the different
relaxation in the two regions. Indeed, at the trailing edge, the material has been just
deformed and is still relaxing. Moreover, this process is speed-dependent as, at very low
and very high speeds the material enters the rubbery and glassy regions respectively,
where it behaves as a solid elastic body, and the energy dissipation is negligible. The
latter is significant at intermediate speed, where proper viscoelasticity effects arise.
Notably, thanks to the well-known computational efficiency of Boundary Element
methods, the present methodology is employed as a valid and numerical more efficient
alternative to Finite Element approaches to assess the multiple contact problem in a
rolling element bearing, where the raceways are linearly viscoelastic, and the rolling
elements are assumed to be rigid. From an applicative point of view, the assessment
of the contact problem is crucial. In fact, it is shown that the distribution of the load
among the rolling elements deviates significantly with respect to the purely elastic case,
with some rollers eventually losing the contact with the raceways for some speed values.
This has consequences not only on the rolling element durability but may impact the
rotor dynamics of the system supported by the bearing. Finally, to corroborate the model, numerical predictions for a rolling element bearing with the outer ring made of
Polytetrafluoroethylene (PTFE) are compared, with good agreement, to experimental
outcomes. This is further supported by a successive comparison between numerics and
experiments, for the outer ring of the bearing is made of Polyamide 6 (PA6).
Crucially, it should be observed that possible implications of the Boundary Element
methodology are not limited to dry contact mechanics, but the integral formulation
could be very useful in lubrication problems involving conformal surfaces. Specifically,
the case of a polymer journal bearing is studied and the importance of the definition of
an appropriate Green’s function to take into account of the conformity of the problem is
highlighted. In fact, making use of the classical half-plane Green’s function significant
deviations are observed in the case of such conforming contact conditions: this aspect is
then critical in design processes.
Furthermore, it is overt that the complex rheology of the viscoelastic material is
strongly coupled with the lubricant viscous losses, thus affecting the bearing capacity
of the system. Hence, the pressure and film thickness distributions for different contact
configurations are determined, highlighting that viscoelastic lubrication is governed
by three parameters, i.e., the Hersey number and the dimensionless velocities of the
interacting pair
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Full text linkWe 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
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