1,720,957 research outputs found
UN’INDAGINE SULLA VARIABILITA’ CICLICA NEI MOTORI A COMBUSTIONE INTERNA UTILIZZANDO PROPER ORTHOGONAL DECOMPOSITION E LARGE-EDDY SIMULATIONS
No full textIl principale obbiettivo della ricerca sui motori a combustione interna (internal combustion engines, ICEs) consiste nell’incremento della potenza erogata a fronte di una contemporanea riduzione di consumi ed emissioni inquinanti. La variabilità ciclica (Cycle-to-cycle variability, CCV) è fortemente legata alla natura intrinsecamente turbolenta della fluidodinamica dei motori a combustione interna, ed i suoi effetti sono nocivi sull’efficienza di combustione, sul consumo di carburante e sulle emissioni inquinanti. A causa delle fluttuazioni nella propagazione del fronte di fiamma, nel rilascio di calore e nella formazione dei prodotti di combustione, la CCV è individuata tra i fattori più limitanti per il raggiungimento di sempre più alte potenze specifiche a fronte di minori consumi. È dunque fondamentale capire e controllare la CCV per migliorare l’efficienza e le prestazioni dei motori. Tecniche sperimentali come la Particle Image Velocimetry (PIV) forniscono un consistente supporto tecnico per l’analisi dell’evoluzione spaziale e temporale dei flussi nei motori. La Proper Orthogonal Decomposition (POD) è stata largamente usata insieme alla PIV per analizzare le caratteristiche del campo di moto dei motori. Negli ultimi anni, diversi metodi basati sulla POD sono stati proposti per analizzare la CCV sui motori. In questo lavoro vengono illustrati la phase invariant POD, la media condizionale, e la decomposizione tripla e quadrupla della POD. Questi metodi sono applicati ad un vasto database di dati PIV sul motore di ricerca ad accesso ottico TCC-III. I risultati sono discussi dando particolare risalto alle capacità di ciascun metodo di dare una stima sia qualitativa che quantitativa della CCV. Un nuovo metodo di decomposizione quadrupla della POD viene proposto e comparato ai metodi presenti in letteratura. Oltre alle tecniche sperimentali, la fluidodinamica computazionale (Computational Fluid Dynamics, CFD) è ormai diventata uno strumento imprescindibile per la comprensione dei complessi fenomeni aero-termochimici che hanno luogo nel cilindro e per guidare lo sviluppo di nuove soluzioni tecniche. Le simulazioni LES (large-eddy simulations) sono lo strumento più indicato per simulare la CCV. In questo lavoro è stato valutato il potenziale della CFD nella simulazione della CCV. Diverse tecniche di analisi della CCV sono state valutate su un dataset di 50 cicli LES sul motore TCC-III in trascinato. L’accuratezza e l’affidabilità delle simulazioni CFD sono insite nei modelli usati per discretizzare il dominio fluidodinamico e per risolvere le equazioni che governano i fenomeni fisici. La strategia di discretizzazione (meshing) assume un ruolo centrale nell’efficienza computazionale, nella gestione dei componenti in movimento nel motore e nell’accuratezza dei risultati. L’approccio overset mesh, chiamato anche Chimera o Composite grid, è stato raramente applicato ai motori, soprattutto a causa delle difficoltà nell’adattamento di questa tecnica alle complessità specifiche della fluidodinamica dei motori. In questo lavoro viene dimostrata l’applicabilità della tecnica overset mesh ai motori a combustione interna, attraverso un approccio di discretizzazione sviluppato appositamente, e ne viene mostrata l’efficacia. 50 cicli LES sono stati calcolati sul motore TCC-III in trascinato. La tecnica di decomposizione quadrupla della POD sviluppata è stata ampiamente applicata per valutare sia l’accuratezza dei risultati simulati, sia l’efficacia del metodo stesso nella comprensione della CCV.The main goal of research on reciprocating internal combustion engines (ICEs) consists in increasing the power output while reducing pollutant emission and fuel consumption. Cycle-to-cycle variability (CCV) is closely coupled with the intrinsic turbulent nature of in-cylinder flow and is detrimental in terms of combustion efficiency, fuel consumption, and tailpipe emissions. Due to fluctuations in flame propagation, heat release, and burnt product formation, CCV is now seen as one of the major limiting factors for higher power output and lower fuel consumption in ICEs. Therefore, it is essential to understand and control CCV to improve the overall engine efficiency and performance. Experimental techniques like particle image velocimetry (PIV) provide a powerful technical support for the analysis of the spatial and temporal evolution of the flow field in ICEs. Proper orthogonal decomposition (POD) has been largely used in conjunction with PIV to analyze flow field characteristics. Several methods involving POD have been proposed in the recent years to analyze engine CCV. In this work, phase invariant POD analysis, conditional averaging, and triple and quadruple POD decomposition methods are introduced and applied to a large database of PIV data from the optically accessible TCC-III research engine. Results are discussed with particular emphasis on the capability of the methods to perform both quantitative and qualitative evaluations on CCV. A new quadruple POD decomposition methodology is proposed and compared to those available in the literature. Besides experimental techniques, Computational Fluid Dynamics (CFD) has become a fundamental tool for understanding the complex aero-thermochemical processes that take place in the cylinder and for driving the development of new technological solutions. Large-eddy simulation (LES) is the most practical simulation tool to understand the nature of CCV. This work investigates the CFD capabilities to simulate CCV. Several methods of analysis were assessed on a 50 LES cycles dataset on the TCC-III engine under motored conditions. The accuracy and the reliability of CFD simulations stands in the models used for the discretization of the fluid domain and for the numerical computation of the governing equations. The meshing strategy plays a central role in the computational efficiency, in the management of the moving components of the engine and in the accuracy of results. The overset mesh approach, usually referred to as Chimera grid or Composite grid, was rarely applied to the simulation of ICEs, mainly because of the difficulty in adapting the technique to the specific complexities of ICE flows. This work demonstrates the feasibility and the effectiveness of the overset mesh technique application to ICEs thanks to a purposely designed meshing approach. 50 LES cycles were performed on the TCC-III engine under motored conditions. The proposed POD quadruple decomposition methodology was extensively applied to assess both the accuracy of the simulated results and the potential of the method itself for understanding CCV
A critical review of flow field analysis methods involving proper orthogonal decomposition and quadruple proper orthogonal decomposition for internal combustion engines
No full textExperimental techniques like particle image velocimetry provide a powerful technical support for the analysis of the spatial and temporal evolution of the flow field in internal combustion engines. Such techniques can be used to investigate both ensemble-averaged flow structures and their cyclic variations. These last are among the major causes of cycle-to-cycle variability of the engine processes (mixture formation, combustion, heat transfer, emission formation), the reduction of which has become a paradigm recently in engine development. Proper orthogonal decomposition has been largely used in conjunction with particle image velocimetry to analyze flow field characteristics. Several methods involving proper orthogonal decomposition have been proposed in the recent years to analyze engine cycle-to-cycle variability. In this work, phase-invariant proper orthogonal decomposition analysis, conditional averaging and triple and quadruple proper orthogonal decomposition methods are first introduced and applied to a large database of particle image velocimetry data from a well-known research engine. Results are discussed with particular emphasis on the capability of the methods to perform both quantitative and qualitative evaluations on cycle-to-cycle variability. Second, a new quadruple proper orthogonal decomposition methodology is proposed and compared to those available in the literature. All the methods are found to be helpful to identify the turbulent structures responsible for cycle-to-cycle variability. They can be equally applied to both experimental and numerical datasets to analyze turbulent fields in detail and to make comparisons
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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