1,720,958 research outputs found
A proposal for a fast passenger ferry operating in Italian coastal island
No full textA research regarding the design of a passenger ferry for Italian coastal islands is in progress at the Dipartimento di Ingegneria Navale di Napoli. The research is based on the evaluation of the optimal speeds in relation whit customer’s expectations and running expenses. The typical service route for this kind of ship is between ten and thirty nautical miles.
The most suitable operating speed was selected after an initial cost-benefit analysis; such speed is an intermediate value between those of present day ferries, which benefit from a significant displacement reduction due to hydrodynamic lift, and that of fully displacing hulls.
The hull was designed as long and slender as possible, to obtain the maximum speed that is economically acceptable, with regard to harbour sizes, stability and routes’ characteristics.
Two model have been tested and towing tank data are presented to explain the process performed to select geometric characteristics of hull to employ.
Finally, a feasibility study is presented to confirm economic interest of proposed solution
STAGGERED CATAMARANS: EXPERIMENTAL DATA AND FEASIBILITY STUDY FOR ENVIRONMENT FRIENDLY SERVICE
No full textIn the last years, displacement hulls for intermediate Froude numbers (Fn<0.6) have been studied at the Dipartimento di Ingegneria Navale of the Università degli Studi di Napoli FEDERICO II (DIN).
Amongst the solutions tested, asymmetric multihulls seem to be quite interesting. Particularly, the scarce amount of experimental data available for staggered catamarans led to a research program in the towing tank, to evaluate the relation between total resistance of ship, stagger of demihulls and displacement.
In this paper we will present the experimental data obtained in the first step of the carried out research. Particularly, hull performances evaluated for three Length to Displacement Ratios (L/1/3 = 4.62, 5.08, 5.76) and four staggers (6, 10, 20, 30 % of LWL) are shown for Fn < 0.5.
The obtained results highlighted the suitability of the studied solutions for inland waterways and especially for urban services, where low environmental impact (wave wash and atmospheric pollution) is growing in social interest. The feasibility of the tested solutions was evaluated through a case study about passenger ferries in urban service. In the paper, general arrangements and cost considerations are presented
Full-Scale Propulsion Measurements on a Planing Pleasure Yacht in Head Sea
No full textFull scale seakeeping trials are rare, especially planing hull and are in
general focused in studying bottom pressures, accelerations and vibrations. In this
paper, a comprehensive description of the experimental setup and analysis of full
scale seakeeping trials propulsion data of a 65 ft planing pleasure yacht is presented.
Torque and rpm have been measured on both propeller shafts during seakeeping
trials in mild sea conditions, along with hull motions and accelerations.
Correlations between hull motions and propulsion data are discussed, both in the
time and frequency domain. Further tests on a shaft sample have been carried out in
order to validate its mechanical properties and hence quantitative results regarding
shaft torque. The main novelty of the present work lays in a detailed analysis of the
propulsion system response of a planing pleasure yacht in mild weather conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Experimental and numerical study of planing hulls in waves
Get PDFIl lavoro presentato nella presente tesi è stato svolto nell’ambito del progetto SOPHYA (Seakee- ping Of Planing Hull YAchts). Il progetto di ricerca e sviluppo è finalizzato all’indagine delle prestazioni imbarcazioni plananti da diporto in termini di tenuta al mare, sicurezza e propul- sione in condizioni di mare medie. Questa indagine è stata condotta attraverso tre approcci complementari: esperimenti in scala modello, prove in mare e simulazioni numeriche.
La tesi si concentra principalmente sulla tenuta al mare degli scafi plananti, in particolare, buona parte del lavoro è stata dedicata allo studio sperimentale e all’analisi dei dati delle prove su modello e scala reale. I risultati sono stati utilizzati come dati di riferimento per le simulazioni CFD al fine di sviluppare un procedura affidabile per le simulazioni di scafi plananti su onda.
È stato condotta un’indagine sperimentale estensiva sullo studio del comportamento non linea- re di scafi plananti in onde regolari e l’effetti dei parametri geometrici dello scafo, della velocità e della pendenza dell’onda sulla risposta ultra armonica dei moti e delle accelerazioni. Ilcontributo principale dello studio è rappresentato dall’ampia analisi della seconda e terza risposta armonica del moto e delle accelerazioni. I risultati rappresentano inoltre un notevole contributo ai dati della serie sistematica di Napoli e forniscono un riferimento dettagliato per futuri studi computazionali.
Le prove di tenuta al mare al vero sono state pianificate ed eseguite, lo yacht è stato com- pletamente strumentato e una boa ondametrica è stata utilizzata per la misurazione direzionale dello stato del mare. È stato sviluppato un metodo innovativo di analisi integrata delle misure di moti a bordo e d’onda al fine di migliorare la stima delle funzioni di trasferimento in scala reale ed è stato investigato l’effetto dei modelli di distribuzione direzionale dell’onda sul risultato. Le funzioni di trasferimento al vero ottenute con l’analisi integrata proposta sono confrontabili con quelle in scala modello.
Sono state eseguite simulazioni in acqua calma e di seakeeping di uno scafo planante utilizzando un codice open source basato su foam-extend. In seguito è stata sviluppata una procedura di pre- processing automatizzata che riduce drasticamente i tempi di pre-simulazione. Questa procedura genera una griglia raffinata ad-hoc per simulazioni di idrodinamica navale e prepara una cartella del caso da simulare pronta per l’uso. La procedura utilizza strumenti di generazione griglie compresi in openFOAM ed altri svilupati appositamente. Le simulazioni di acqua calma hanno mostrato una una sottostima dell’assetto in corsa e della resistenza alle alte velocità, tuttavia le simulazioni di seakeeping mostrano risultati molto più fedeli ai dati sperimentali in termini di funzioni di trasferimento. Sono inoltre stati implementati nuovi strumenti per le simulazioni che debbano riprodurre fedelmente le condizioni della vasca navale, come accelerometri virtuali e nuove condizioni cinematiche più fedeli al reale fissaggio del braccio di rimorchio.
I solutori e gli strumenti sviluppati sono stati in seguito utilizzati per studiare l’effetto delle variazioni della forma dello scafo sulle prestazioni di tenuta del mare di otto diverse varianti. I risultati sperimentali dello scafo con le migliori prestazioni sono comparabili con quelli ottenuti dalle simulazioni.The work presented in this thesis has been carried out as part of the SOPHYA (Seakeeping Of Planing Hull YAchts) project. The research and development project is aimed at the investigation of the performances of planing pleasure-boats in terms of sea-kindliness, safety and powering in mild weather conditions. This investigation is pursued via three complementary approaches: model scale experiments,sea trials and Numerical simulations.
This thesis is mainly focused on the study of planing hulls seakeeping, in particular, a large part of this work has been dedicated to experimental investigations and data analysis both in model and full scale. The results of towing tank tests have been then used as reference data for CFD simulations with the aim of to develop a reliable computational framework for seakeeping simulations of planing hulls.
A novel experimental work has been carried out in order to investigate nonlinear behavior of planing hulls in regular waves and the effects of geometrical parameters, speed and wave steepness on higher harmonic response of hull motions and accelerations. An extensive analysis of the second and third harmonic response of motion and accelerations is presented, adding valuable results to the Naples Systematic Series data set and providing detailed benchmark data for future computational studies.
Full scale calm water and seakeeping trials have been carefully planned and executed, the yacht has been fully instrumented and a wave buoy has been used for directional sea state mea- surement. An innovative integrated analysis method of on-board and wave measurements has been developed in order to improve full scale transfer functions estimation. The effect of wave directional distribution models on the estimated transfer functions has been investigated. The results show a remarkable agreement with model scale experimental results.
Planing hull calm water and seakeeping simulations have been performed using open source CFD code. An open source fully automated pre-processing procedure has been developed to drastically reduce time-to simulations. The procedure generate a mesh refined ad-hoc for planing hullsimulations and a ready-to-run case folder using OpenFOAM built-in and custom tools.
Calm water simulations showed an underestimation of the running trim angle and resistance at high speeds. Seakeeping simulations however showed much better agreement with experimental results in terms of motion transfer functions. New simulation tools have been implemented for the specific case of reproducing towing tank conditions, such as virtual accelerometers and new restraint capabilities that are more faithful of the real towing arm restraint conditions. The tested simulation framework has been used to investigate the effect of hull form variations on seakeeping performances of eight alternative hulls. Experimental results on the best performing hull alternative show comparable results with simulations
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