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Advanced Methods for Volumetric Pumps Simulation and Characterization
No full textLa tesi tratta lo sviluppo di tecniche di simulazione avanzate per la previsione del comportamento di pompe volumetriche, sia in termini di NVH, sia in termini fluidodinamici. Le metodologie di analisi presentate, costituiscono 3 strumenti essenziali da utilizzare sia nelle prime fasi della progettazione di nuove macchine, sia per l’implementazione di modifiche progettuali per il miglioramento di macchine esistenti. Questo tipo di strumenti di indagine si rendono particolarmente efficaci nel fornire ai progettisti indicazioni sulle strategie da intraprendere, evitando spreco di risorse nello sviluppo di soluzioni tecniche non vantaggiose.
Il primo metodo di analisi presentato riguarda lo studio di pompe a palette mediante un approccio cinetostatico. In particolare, nello studio sono state affrontate le problematiche legate al funzionamento di pompe dotate di palette con doppia testa a profilo circolare. Attraverso un’approfondita analisi cinematica è stato mostrato come risolvendo le equazioni del moto, parametrizzando l’intero sistema alle caratteristiche geometriche di tali palette, fosse possibile esplicitare dei criteri di ammissibilità riguardanti la geometria delle palette. Assicurando la continuità del moto della paletta, intesa come cedente di un sistema camma-punteria, e controllando le forze scambiate nella zona di contatto, sono stati elaborati i criteri di scelta che aiutano alla scelta delle geometrie meritevoli di approfondimenti tecnici. Monitorando tali aspetti, si escludono le geometrie che potrebbero introdurre moti discontinui ed eccessivi fenomeni di usura.
In parallelo ad uno studio cinematico, è stato mostrato come sia possibile mediante un modello a parametri concentrati estrapolare le prestazioni e analizzare dettagliatamente il comportamento di pompe volumetriche. Nella fattispecie, è stato presentato un modello applicato a pompe ad ingranaggi esterni. La validazione del modello è stata ottenuta mediante la riproduzione dei valori di pressione e portata media, nonché le fluttuazioni dell’onda di pressione in mandata, ottenuti attraverso opportuni test. Il modello è stato implementato risolvendo un articolato sistema di equazioni di continuità generate seguendo il modello di Bernoulli. Per ogni orificio attraverso cui il sistema scambia portata tra volumi adiacenti, è stata elaborata un’equazione di continuità tarata mediante la calibrazione di coefficienti di flusso. Per aumentare la precisione del modello è stato implementato un modulo che calcola l’effetto della flessione degli alberi delle pompe sulla dimensione degli orifici e sulle portate scambiate. Ai fini della validazione, il modello è stato applicato a diversi casi studio. L’elevato livello di dettaglio dei risultati ottenuti ha permesso la progettazione di diverse soluzioni migliorative e il successivo sviluppo e test dei prototipi ha confermato l’accuratezza del modello, garantendone l’affidabilità anche nello sviluppo di migliorie tecniche.
Il terzo metodo di analisi proposto è stato sviluppato con l’obiettivo di fornire un aiuto alla prevenzione di fenomeni di emissione acustica e vibrazionale indesiderati quando queste macchine sono integrate in sistemi meccanici complessi. Lo studio è stato svolto analizzando l’integrazione di un idrostato in una trasmissione CVT. La caratterizzazione vibro-acustica del sistema è stata fatta attraverso una analisi di risposta in frequenza del sistema, riprodotto mediante un modello ad elementi finiti. La validazione del modello è stata fatta calibrando i parametri modali del sistema, riproducendo i fenomeni vibratori caratterizzati da una analisi operativa iniziale. Con il modello validato è stato poi possibile valutare gli effetti in termini di NVH delle diverse soluzioni di vincolamento e smorzamento.The Thesis deals with the development of advanced techniques for volumetric pumps NVH and fluidynamic behaviour characterization. The methodologies here presented constitute 3 fundamental tools for the early stages of volumetric machines design or for the implementation of enhancement strategies for existing pumps. Similar approaches represent fast and reliable tools for the evaluation of design strategies, helping the final users to detail the design just for eligible solutions.
In first instance, within the manuscript has been reported a kinetostatic approach to the design of balanced vane pumps equipped with twin lip vanes. Thanks to a deep investigation of the mechanism kinematic, a set of vane geometry admissibility maps has been developed and presented. Such maps have been obtained expressing the kinematic as function of the vane geometrical parameters. The geometrical constraints have been obtained obliging the vane lift law to respect a smooth and continuous motion. Moreover, the imposition of additional constraints, related to the contact loads arising from the pump functioning, gives the opportunity to dispose of a further indicator for the choice of the best vane solutions for a given cam-ring. The residual admissible geometries represent the vanes that reasonably ensure limited contact detachments and consequently proper NVH behaviour and limited lubricant leakages.
In parallel to a kinematic approach, a lumped parameters modelling methodology for the study of the volumetric performances has been presented. Despite such approach might as well be applied to the whole volumetric machines field, within the manuscript the application to gear pumps have been reported. The model has been validated reproducing the operative delivery pressure ripple and flowrate of a tested sample pump. Here, the Bernoulli’s equation has been implemented for the continuity equations system resolution, introducing a capillary description of the exchange orifices. The orifices flow parameters tuning has been extensively described corroborating the model reliability and flexibility. With the purpose to reproduce the efficiency gain observed at increasing delivery pressure, the instantaneous shaft bending calculation has been integrated within the model. The validated model has then been deployed for the study of volumetric efficiency enhancement solutions for a helical gear pump. Several solutions have been numerically analyzed thanks to the accurate model postprocessing tool that has allowed to evaluate and resolve local issues and leakages. The most effective solutions have been implemented and the results of the consequent test campaign have confirmed the excellent efficiency improvements suggested by the model.
Aside from the analysis of the internal phenomena, the manuscript also deals with the integration of the machines within the final systems. In particular, the study has been oriented to the investigation of NVH containment solutions. For the scope a portion of a CVT has been studied with particular focus on the integration of the hydrostatic module. The NVH characterization has been performed modelling the system with a finite element approach and implementing a frequency response analysis within an adequate investigation frequency field. The model has been validated reproducing the operative natural frequencies of the system. The postprocessing of the data has been included within the manuscript. The validated model has then been adopted to evaluate the influence of different enhancement solutions. In this context the different design solutions have been implemented by means of concentrated elements. The results of the most effective enhancements have been reported and extensively discussed highlighting the reliability of the model for the design of improvement solutions and for the integration within the early stages of novel systems development
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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