1,720,956 research outputs found
METODOLOGIE E STRUMENTI PER IL PROGETTO DI SISTEMI ELETTRICI NAVALI E MARINI
No full textLo scopo della tesi è quello di presentare metodologie e strumenti innovativi, applicabili ai sistemi elettrici navali, in grado di affrontare le problematiche date sia dal processo di progettazione convenzionale che dalla volontà di installare a bordo nuovi sottosistemi, dati i requisiti crescenti degli armatori e viste le stringenti normative sull'inquinamento. Le metodologie e strumenti analizzati possono migliorare la conoscenza del sistema già nelle prime fasi di progettazione. L'obiettivo è definire tutte le scelte progettuali possibili prima della fase contrattuale. Gli imprevisti legati all’utilizzo di soluzioni innovative possono portare a conseguenze dannose per il sistema nave. Tali metodologie e strumenti forniscono dati coerenti su cui basare le decisioni di progettazione, valutando diverse configurazioni e riducendo inoltre i tempi e i costi di progettazione. Riducendo l’impegno richiesto per ottenere le stesse informazioni, ovvero a parità di tempo e risorse investite prima di siglare il contratto, si possono proporre soluzioni realizzabili e di cui si può stimare con più accuratezza il prezzo. Inoltre, nuovi sottosistemi possono essere integrati evitando un aumento incontrollato dei costi.
In questa tesi viene effettuata un'ampia rassegna dello stato dell'arte, per consentire la comprensione del contesto, del perché tecniche innovative possono essere utilizzate come un aiuto nella progettazione. Ogni punto è discusso concentrandosi sullo scopo di questa tesi, presentando così argomenti, bibliografia, e considerazioni volte ad indirizzare il lettore a comprendere l'impatto dei nuovi strumenti per la progettazione di impianti elettrici navali.
In particolare, dopo un primo capitolo dedicato all’introduzione delle navi a propulsione elettrica, in cui viene descritto come tali navi si siano evolute. Nel secondo capitolo, vengono presentati sistemi di distribuzione innovativi e nuovi requisiti soprattutto per navi da crociera e militari. Dato il significativo impatto di tali innovazioni, un excursus su questi due temi è fatto con riferimento alla bibliografia più recente.
Nel terzo capitolo, invece, si effettua una discussione ragionata sul processo di progettazione convenzionale delle navi. In aggiunta a questo viene effettuata un'analisi approfondita del processo di progettazione dei sistemi elettrici, per spiegare il contesto in cui un approccio innovativo alla deve essere integrato.
Il quarto capitolo è dedicato alle nuove tecniche di progettazione e di come questi strumenti, assieme all’utilizzo di software specifici, possano essere utili per migliorare la progettazione dell’intera nave. In questo contesto, viene introdotto il concetto di uno spazio riservato dedicato al sistema elettrico, il cui impatto sul sistema nave può essere valutato sin dalle fasi iniziali del progetto.
Nel quinto capitolo viene presentato il caso di studio di questa tesi. Successivamente, la nave di riferimento viene riprogettata con due diversi sistemi di distribuzione in corrente continua. Entrambe le soluzioni sono confrontate in termini di volumi e pesi verificando così la loro fattibilità nonché la validità del metodo di redesign proposto.
Le soluzioni innovative proposte possono però impattare negativamente sulle prestazioni del sistema elettrico. Per questo motivo, nel capitolo sei, si è analizzato il loro impatto sull’impianto elettrico al fine di prevenire problemi di integrazione. Nello specifico si sono analizzati gli effetti che la propagazione dei disturbi ad alta frequenza, causati dai convertitori elettronici, può avere su cavi di distribuzione e trasformatori, validando sperimentalmente il modello di quest’ultimo.
Nel settimo capitolo, infine, servendosi dei dati precedentemente ricavati, si è usato un software modulare per la simulazione del sistema elettrico della nave di riferimento al fine di valutare l’accuratezza e il carico computazionale di diversi modelli propostiThe aim of this thesis is to present an innovative methods and tools, applicable to the shipboard integrated power system, able to address the issues given by both the conventional design process and the desire to install on board new subsystems, giving both the ever-increasing ship-owners’ requirements and pollution regulations. Methods and tools analyzed throughout this thesis work can enhance the knowledge of the system already in the early stage design phases. The final goal is to define the feasible design choices before the contract phase. Indeed, such commitments can lead to harmful consequences since the project may not be feasible at the end due to unforeseen issues related to the exploitation of innovative power system solutions. Such methods and tools are a mean to provide consistent data on which base innovative design decisions exploring different design choices and thus lowering the design times and costs. By reducing the effort required to obtain the same information, or with the same amount of time and resources invested before signing the contract, feasible solutions can be proposed and the price of which can be estimated more accurately. Furthermore, innovative subsystems can be integrated avoiding an uncontrolled cost increase.
In this thesis, a wide review of the state of the art is done, to allow understanding the context, why such innovative techniques can be used as an aid in design. Each point is discussed focusing on the aim of this thesis, thus presenting arguments, bibliography, and considerations tailored to direct the reader to comprehend the impact of new tools in the ship power systems design.
In particular, after a first chapter dedicated to the introduction of electric propelled ships, in which are described how such ships have evolved. In the second chapter, innovative distribution systems and new requirements are presented, especially for cruise and military ships. Given the significant impact of these innovations, an excursus of both these two topics is given, referring to recent literature and research activities.
In the third chapter, however, a reasoned discussion on the conventional ship design process is depicted. In addition, an in-depth analysis of the onboard ship systems design process is carried out to explain the context in which the innovative design approach has to be integrated.
The fourth chapter is dedicated to new design methods and tools, together with the use of specific software, and how they can be useful for improving the entire ship design. In this scenario, the new concept of space reserved on board is proposed to accommodate the power system. The space reservation impact on the overall ship design can be evaluated from the early stage design phase.
In the fifth chapter the case study of this thesis is presented. Subsequently, the reference ship is redesigned with two different dc distribution systems. Both the solutions are compared in terms of volumes and weights, thus verifying their feasibility and the validity of the proposed redesign method.
However, the innovative solutions proposed can have a negative impact on the performance of the power system. For this reason, in chapter six, their impact on the onboard power system has been analyzed in order to prevent integration issues. Specifically, the high frequency disturbances propagation has been assessed both in power cables and transformers, experimentally validating the latter model.
Finally, in the seventh chapter, using the data previously obtained, a modular software was used to simulate the reference ship power system in order to evaluate the accuracy and computational load of the various models proposed
Voltage and frequency regulation in high power AC islanded microgrid with static converter interfaced generators
No full textIn this paper a conservative approach to build a Power Electronic Power Distribution System (PEPDS) has been used, introducing into an existing islanded AC system a Static Converter Interfaced Generator (SCIG). The paper tries to assess the power quality issues (in terms of v/f regulation) that can possibly arise when integrating conventional mechanical-based generators with new ones in an islanded power system, using a mathematical modelling approach. Two different phase regulators for the SCIG output voltage vector have been evaluated and compared, depending on the operative requirements of the SCIG prime mover (frequency regulation or fixed power injection). Finally, a set of simulations has been performed to assess the effect of the SCIG grid-side regulators parametric variations on the system's v/f regulation performance
Open Challenges in Future Electric Ship Design: High-Frequency Disturbance Propagation in Integrated Power and Energy Systems on Ships
No full textShipboard power systems have made great progress since Jacobi's experiment in the late 1830s (i.e., the first electric propelled boat). Today, the shipboard power system design process is facing significant changes, mostly due to the improvements both in power electronics and battery technology. (For instance, the MF Ampere entered into service in 2015 as the world's first electric battery-powered passenger and car ferry.) Moreover, the power systems sector is also undergoing significant changes due to both the ever-increasing requirements of ship owners and the enforcement of recent efficiency and pollution regulations. Currently, power electronics converters increase in both power and number in a modern Integrated Power and Energy System (IPES), exploiting different power system architectures
Filtered Feedback Control on DC Microgrid to Power a High-Performance Battery-Based Cutter Dredger
No full textIn the marine industry, resilience and flexibility in use are among the most important targets to be attained. These two goals are even more crucial when considering specific vessels like cutter dredgers. The latter are in charge of providing the very specific function of soil removal, which constitutes a high-power load to be transiently powered from the onboard power plant. In this paper, a ring DC grid is proposed to exploit the presence of a Battery Energy Storage System (BESS) in supplying the onboard loads of a dredger. An advanced control system on DC power electronics interfaces is designed to guarantee the power quality requirements while preserving the diesel units. A realistic load profile is considered in the synthesis of control functions, where a filtered feedback is adopted to optimally share the generating effort. Significant transients are discussed in order to demonstrate the control performance in managing power sources and BESS
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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