1,720,958 research outputs found
Minimizzazione delle perdite AC in avvolgimenti di tipo Hairpin realizzati e progettati per la manifattura additiva.
No full textNegli ultimi anni, la crescente richiesta di densità di coppia e potenza più elevate ha portato all'adozione di avvolgimenti hairpin nelle macchine elettriche, in particolare in quelle destinate ad applicazioni automobilistiche. Tuttavia, questa topologia è piuttosto sensibile alle perdite AC, rendendo la loro riduzione una delle principali sfide.
Questo lavoro affronta diversi aspetti della progettazione volti a migliorare le prestazioni delle macchine elettriche per la trazione, con particolare attenzione all'incremento della densità di potenza e all'affidabilità. Inizialmente, si richiamano le formulazioni analitiche esistenti per la valutazione delle perdite AC nella parte attiva degli avvolgimenti hairpin. Successivamente, viene esplorata una formulazione analitica universale che considera anche design non convenzionali, come configurazioni asimmetriche e segmentate. Di conseguenza, l'attuale formulazione viene estesa, aggiornata e validata attraverso simulazioni agli elementi finiti e test sperimentali condotti su sezioni di motore.
Per entrambe le configurazioni vengono descritti i principali vantaggi e le eventuali problematiche progettuali, insieme a linee guida per la realizzazione pratica e il collegamento dei conduttori. Si offre inoltre un'analisi dettagliata del processo produttivo tramite fabbricazione additiva, con l'obiettivo di individuare strategie che possano superare le limitazioni dei metodi di produzione tradizionali, concentrandosi in particolare sull'ottimizzazione degli avvolgimenti hairpin mediante tale tecnologia. Una volta identificato un processo produttivo idoneo, si conduce un'analisi approfondita dei materiali per ridurre al minimo le perdite AC complessive nella macchina, limitando al contempo l'impatto ambientale.
Infine, viene analizzata la fattibilità e i benefici derivanti dall'impiego di avvolgimenti hairpin asimmetrici prodotti tramite fabbricazione additiva. Questa analisi si basa sui modelli analitici e agli elementi finiti sviluppati, con test di validazione su un prototipo di avvolgimento.
Oltre allo studio delle parti attive dei conduttori, viene condotta una stima accurata del comportamento AC nelle testate con sezioni trasversali costanti e variabili utilizzando un modello 3D agli elementi finiti. I risultati si concentrano non solo sulla distribuzione della densità di corrente per il layout specifico, ma anche sul fattore di perdita AC, fornendo una stima delle perdite in funzione dell'aumento della frequenza.In the last years the increasing demand of higher torque and power densities has led to the adoption of hairpin windings in electrical machines, mainly in those intended for automotive applications. However, this winding topology is quite sensitive to AC losses, hence one of their main challenges is represented by their reduction.
This work deals with different design aspects related to the enhancements of some performance figures of rotating electrical machines for traction applications, above all power density and reliability. First, the existing analytical formulations for the evaluation of active length AC losses for hairpin windings are recalled. Then, a general analytical formulation is investigated also for non-conventional hairpin windings design, such as asymmetrical and segmented configurations. Therefore, the existing analytical formulation is extended, updated and validated through finite element simulations and experimental tests performed on motor portions, so called motorette.
For both the configurations, the main advantages and possible design constraints are illustrated, along with guidelines for the practical realization and connections of the conductors. Additionally, a detailed examination of the additive manufacturing production process is provided to identify possible strategies for overcoming the design limitations of conventional manufacturing processes for hairpin windings with a detailed focus on additive manufacturing optimisation of solid conductors. Once a suitable production process is selected, a detailed material analysis is conducted to minimize total AC losses in the machine while limiting environmental impact.
Finally, the feasibility and benefits of adopting an additive manufacturing -produced asymmetrical hairpin winding are investigated. The analysis is carried out using the developed analytical and finite element models, with validation tests performed on a hairpin winding prototype.
In addition to the investigation of active parts of solid conductors, a detailed estimation of the AC behaviour in end windings with both constant and variable cross-sections is performed using a 3D finite element model. The results focus not only on the current density distribution for the specific layout but also on the AC-to-DC trend, providing a qualitative estimation of the increase in losses as frequency rises
On the AC Losses in the End Conductors of Hairpin Windings
Full text linkIn the last years, several resources have been employed to increase torque and power density values in electrical machines, especially in those intended for transport applications. In this context, the adoption of hairpin conductors is spreading thanks to their inherently high fill factor. Their main drawback is represented by their sensitivity to high-frequency phenomena, which can have a significant impact on the Joule losses and thus on the overall efficiency.
While several researches have recently focused on ways to model and reduce such high-frequency losses in the slots, i.e. within the conductors’ active sides, a few data are available on their impact in the end winding regions.
This work provides an investigation on the AC losses occurring in the end conductors of a hairpin winding traction motor. The losses are determined through 3D finite element simulations for a wide frequency range, and compared against those occurring in the active part of the machine.
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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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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