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Prediction models for the dynamical behaviour of multi-phase annular seals
Full text linkSempre maggior interesse è stato dedicato nelle ultime due decadi nello studio e sviluppo di pompe multifase. Le pompe multifase elaborano miscele di fluidi immiscibili (compressibili e non) ad alte velocità e potenze specifiche per stadio in modo da ridurre dimensioni e costi. Tali peculiarità rendono questo tipo di turbomacchine molto attraenti in settori industriali come l’Oil&Gas, sia per applicazioni sottomarine che in superficie, industria chimica e farmaceutica. Di primaria importanza, in fase di progettazione della macchina, è la valutazione della stabilità rotordinamica della turbomacchina, in modo da assicurare alta affidabilità e continuità di servizio specialmente quando i lavori di manutenzione sono difficili e costosi. A tal riguardo, la valutazione dei coefficienti rotordinamici della tenuta è di solito realizzata attraverso l’uso di modelli semplificati di flusso medio, basate sulle equazioni di Navier-Stokes mediate sul meato fluido (i.e. la distanza rotore-statore); la chiusura del problema si ottiene attraverso l’utilizzo di correlazioni sia numeriche che sperimentali. I modelli di flusso medio sono caratterizzati da alcune importanti peculiarità come facilità di utilizzo e velocità. Mostrano tuttavia qualche punto debole. Nel caso specifico delle pompe multifase, ad esempio, l’applicazione delle correlazioni monofase al campo multifase, può portare a inaccuratezza e risultati fuorvianti. A tal riguardo, lo scopo di questa ricerca di dottorato è quello di proporre un nuovo modello di flusso medio per la caratterizzazione della risposta strutturale di una tenuta anulare in pressione operante in regime di flusso multifase. Il modello proposto è basato sull’ipotesi principale di una stratificazione regolare dei due fluidi. È stato ipotizzato che il liquido venga centrifugato verso lo statore, lasciando il rotore in contatto con il solo gas. Tale premessa rende possibile derivare un modello di flusso medio a due strati per ognuna delle due fasi.
Chapter 1 introduce la notazione abituale per l’analisi di stabilità strutturale. Viene delineato il modello di risposta strutturale della tenuta.
Chapter 2 riesamina la letteratura nel campo della caratterizzazione e modellazione delle tenute anulari in pressione in regime monofase. Vengono scrutinati sia i metodi CFD che i modelli a flusso medio. Infine, entrambi i metodi vengono comparati con i risultati sperimentali.
Chapter 3 tratta della modellazione delle tenute anulari multifase. Il capitolo in particolare analizza il modello bifase più adottato in letteratura: il modello bifase omogeneo. Viene introdotto una revisione globale della letteratura. Una nuova formulazione generale delle condizioni al contorno è proposta. La valutazione del modello è fatta attraverso il confronto con i risultati sperimentali.
Chapter 4 presenta il nuovo modello stratificato. Vengono introdotte le equazioni di flusso medio. Le correlazioni sia degli integrali del flusso di quantità di moto che dei fattori di attrito sono modellate per ognuna delle due fasi in funzione dello specifico regime di flusso (turbolento piuttosto che laminare). Le portate predette mostrano buon accordo con i risultati sperimentali.An increasing interest has been devoted in the last two decades in the study and development
of multiphase pumps. Multiphase pumps elaborate mixtures of immiscible fluids (both
compressible and not) at high speed and power density per stage in order to reduce size and cost.
These peculiarities make this kind of turbomachinery very attractive in different industrial sectors
such as Oil&Gas, both for sub-sea and topside applications, chemical and pharmaceutical
industry. Of primary importance, in the machine design phase, is the evaluation of the turbomachinery
rotordynamic stability, to ensure high reliability and service continuity specially
when maintenance works are difficult and expensive. In this respect, the evaluation of the seal
rotordynamic coefficients is usually achieved through simplified bulk flow models, based on the
Navier-Stokes equations averaged over the fluid meatus (i.e. the rotor-stator clearance); the
problem closure is achieved with the aid of both numerical and experimental correlations. Bulk
flow models are characterized by some important peculiarities such as ease of use and fastness.
They show however some weakness. In the specific case of multiphase pumps, for example,
the application of the single phase correlations to the multiphase field can lead to inaccuracy
and misleading results. In this regard, the aim of this doctoral research is to propose a new
bulk flow model for the characterization of the structural response of an annular pressure seal
operating in the multiphase flow regime. The proposed model is based on the major hypothesis
of a smooth stratification of the two fluids. It is hypothesized that the liquid is centrifuged
toward the stator, leaving the rotor in contact only with the gas. This assumption allows to
derive a two-layer bulk model for each of the two phases.
Chapter 1 introduces the usual notation of the structural stability analysis. The model of
the seal structural response is outlined.
Chapter 2 reviews the literature in the field of the single phase annular pressure seal
modeling and characterization. Both CFD and bulk flow models are scrutinized. Finally, both
the methods are compared with experimental measurements.
Chapter 3 deals about the multi-phase annular seal modeling. The chapter especially
analyzes the widest adopted two-phase bulk model in literature: the homogeneous two-phase
model. A global review about the specific literature is introduced. A new general formulation
of the boundary conditions is proposed. Model assessment in done through the comparison
with experimental results.
Chapter 4 presents the new stratified bulk flow model. Bulk flow equations are introduced.
Correlations of both momentum flux integrals and friction factors are modeled for each of the
two phases depending on the specific flow regime (turbulent rather than laminar). Predicted
mass flow rates show good agreement with experimental results
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
L'indirizzo seguito dalla Commissione
No full textProposta di uno schema di regolamento di organizzazione dei musei statali, ai fini della loro valorizzazion
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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