1,721,297 research outputs found
High Speed Synchronous Machines: Modeling, Design and Limits
No full textQuesto lavoro di tesi riporta i risultati di tre anni di attività svolte durante il XXXV ciclo del corso di dottorato in Ingegneria Elettrica e dell'Informazione del Politecnico di Bari.
L'obiettivo principale del lavoro è la definizione di una completa procedura di progettazione di macchine elettriche sincrone ad alta velocità, tra cui le macchine sincrone a riluttanza pura, le macchine sincrone a riluttanza assistita da magneti permanenti e le macchine sincrone a magneti permanenti isotrope.
Un'originale metodologia di progettazione sarà prima proposta per le macchine sincrone a riluttanza; tale metodologia è basata su modelli analitici ed opportune simulazioni agli elementi finiti utili a correggere le imprecisioni dell'approccio puramente analitico. Il metodo proposto è in grado di considerare sia le problematiche elettromagnetiche che quelle termiche e strutturali, nonché i loro diversi requisiti nell'ambito di una progettazione di una macchina ad alta velocità. Infatti, la metodologia di progettazione è in grado di portare in conto sia le non-linearità magnetiche che le limitazioni strutturali e l'incremento delle perdite nel ferro di statore e rotore. L'approccio adottato permette di ottenere macchine ottimali sia da un punto statorico che rotorico, bilanciando tutti i sopracitati aspetti multifisici e mantenendo costante o la densità di corrente o il sistema di raffreddamento. Saranno esaminati differenti tipi di materiali ferromagnetici, in particolare i materiali basati sulla tecnologia a ferro-silicio (SiFe) e quelli basati sul Cobalto (CoFe), con lo scopo di individuare i limiti di potenza di una macchina a riluttanza pura.
La stessa filosofia di progettazione sarà applicata al caso di macchine a riluttanza assistita da magneti permanenti, dove l'inserimento di questi ultimi all'interno delle barriere di flusso costituisce un ulteriore grado di libertà all'interno della progettazione; l'inserimento del giusto volume di magnete rappresenta la strategia più comune per aumentare in maniera significativa le prestazioni di un motore a riluttanza pura, sia in termini di densità di potenza che di fattore di potenza. Sarà mostrato come è possibile ottimizzare una macchina a riluttanza assistita in modo da soddisfare tutti i vincoli elettromagnetici e strutturali che insorgono quando la velocità di progetto aumenta. Tale metodologia sarà applicata considerando magneti sia a bassa (es. Ferrite) che alta (magneti in terre rare, es. NdFeB) densità di energia.
Infine, sarà analizzato il caso delle macchine a magneti permanenti superficiali utilizzando la stessa strategia di progettazione ibrida-analitica, ponendo particolare attenzione alla progettazione della camicia di contenimento dei magneti permanenti necessaria ad alte velocità; infatti, sia il fenomeno di espansione termica che le problematiche legate alle forze centrifughe in gioco devono essere correttamente portati in conto.
La metodologia proposta, applicata alle tre tipologie di macchine, costituisce un approccio flessibile, sistematico e generale, utile per dedurre alcune linee guida di progettazione in accordo con date assunzioni e scelte di progetto.
Le considerazioni fatte saranno validate sperimentalmente su quattro diversi prototipi.This thesis reports the results of the three-years activities carried out during the XXXV cycle of the Ph.D. course in Electrical and Information Engineering of Politecnico di Bari.
The main goal of this work is the definition of a comprehensive design procedure for high-speed synchronous machines, including synchronous reluctance (SyR), permanent magnet assisted synchronous reluctance (PMaSyR) and surface mounted permanent magnet (SPM) machines.
An original design approach is first proposed to the SyR scenario based on analytical methods and few finite element simulations capable of correcting the inaccuracies of the analytical approach. The proposed methodology takes into account both the electromagnetic, thermal and structural issues and their conflicting requirements when a high-speed design scenario is considered. In fact, magnetic non-linearities, rotor structural limitations and the rise of both stator and rotor iron losses are all considered. The adopted design approach allows achieving optimal stator and rotor geometries balancing all these competitive multi-physics aspects and keeping constant either the cooling system capability or the current density.
Both silicon-iron (SiFe) and cobalt-iron (CoFe) alloys with optimized magnetic and mechanical performance are examined to assess the maximum capabilities achievable with a SyR machine technology.
The same design philosophy is then applied to the PMaSyR case, when the degrees of freedom are increased by the insertion of the proper amount of PM volume within the rotor flux barriers, which is the most common design strategy used to significantly increase their performance in terms of both power density and power factor. It will be shown how a permanent magnet assisted synchronous reluctance machine can be optimized to satisfy all the electromagnetic and structural constraints arising as the maximum operating speed increases. This will be done considering a variety PMs material, including low energy density PMs (e.g., Ferrite) and high energy density ones (e.g., rare earth materials such as NdFeB).
Finally, the SPM design case is analyzed with the same hybrid-analytical workflow, with special attention on the sleeve design as the speed increases; indeed, both thermal expansion and centrifugal forces must be accurately taken into account.
The proposed design procedure, either applied to SyR, PMaSyR or SPM cases respectively, constitutes a flexible, systematic and general approach which is useful to infer design guidelines according to given assumptions and design choices.
Experimental results on four different prototypes validate the design approach
"Coreografia multimediale per il progetto Welt Labyrinth"
No full textProgetto di una scenografia dinamica, ad alto profilo tecnologico e multimediale. L'utilizzo del digitale rivoluziona nella scena il rapporto fra architettura, suolo e paesaggio
The Educational Civic Path in Southern Italy: What Determines Behaviors Toward Food Waste Among Students in Campania Region?
No full textFood waste prevention has become an issue of international
concern, with Sustainable Development Goal 12.3 aiming to
halve per capita global food waste by 2030. Students are
most inclined to waste food, and thus they need to be investigated.
The study focused on students’ behavior toward food
waste in Campania region (Southern Italy) to address the educational
civic path expected by the Ministry of Education. A
web survey involving 409 students was used to investigate
the food waste behavior within the framework of the Theory
of Planned Behavior. The findings suggest that concern about
food waste, moral attitude and perceived behavioral control
influence individuals’ intentions to act and this in turn, translates
into correct behavior toward food waste. The recognition
of the factors that affect students’ behavior toward food waste
represents an important starting point to develop and implement
different anti-waste strategies at national and
regional levels
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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