1,720,958 research outputs found
Wave Drift Forces Estimation for the Preliminary Design of Dynamic Positioning Systems
No full textIn present work, a simplified methodology able to provide a sufficiently accurate assessment of wave drift forces is presented, with the aim of providing a procedure which may be applied in the preliminary stages of the design, when the technical data of the ship (such as the hull forms) are not yet available, and only main hull parameters are present. In particular, the 3D panel seakeeping program PRECAL, developed at Cooperative Research Ships (CRS) is utilised. At first, its capabilities are verified comparing numerical results with literature data, showing the code reliability. Then, a series of simplified ellipsoidal hull forms have been analysed and compared with more complex hull forms in order to identify a criterion of equivalence, which may be used when a detailed description of the hullform is not available. Results show that the proposed simplified methodology is reliable and enough accurate to allow a proper sizing of the propulsion and manoeuvring systems of a ship with dynamic positioning requirements in the preliminary stage of the design
A Momentum Theory Approach to the Seakeeping of Planing Crafts
No full textLeisure boats market has constantly grown during the latest years entailing an increasing need of design tools, dealing with technical problems like seakeeping of planing boats, whose complexity still present a high challenge for designers.
The present paper describes a methodology for the calculation in time domain of the vertical motions of a planing boat in head waves, capable of predicting the non-linear vertical motions of the boat in both regular / irregular head waves. The formulation makes recourse to a ‘strip-theory’ approach to get the 3D hydrodynamic forces as a linear superposition of the sectional forces. The determination of the 2D planing forces is based on ‘momentum theory’ using Wagner’s wedge-theory to model the sectional characteristics, while non-linear Froude-Krylov forces are directly evaluated accounting the relative motions at each cross-section. Moreover, from the time-series of the vertical motions an overall passenger comfort index and slamming pressures are evaluated.
A validation of the code is presented against the model-test results available in literature
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
Automatic Parametric Hull Form Optimization of Fast Naval Vessels
No full textThe present work shows the outcomes of a research project among the Department of Naval Architecture and Marine Engineering of the University of Genoa and Cetena S.p.A. for the Italian MOD in the frame of National Defence Research Plan. An automatic optimization study of the fore hull forms of a fast frigate is presented; it has been performed with a proper integration of a commercial optimization system, a parametric geometric modelling software and two different ship hydrodynamic analysis tools to predict the steady (wave resistance) and unsteady (seakeeping) performance of each design candidate. The fully automatic optimization algorithm, used to evaluate several thousands of design alternatives, takes into account a constrain set composed both by geometrical tolerances and minimum stability characteristics of the hull defined in a preliminary design study mentioned and briefly recalled in the paper.
The parametric definition of the ship hull geometry accurately devised to represent the original hull form solution and to include as many variable shapes and possible, still granting a good fairing of each solution, is described in the paper as well as the technical details of the optimization set up, in terms of high level software architecture; analytical definition of the objective functions; imposition of the design constraints and selection of the optimization strategy.
Interesting conclusions are drawn in the end of the paper from the results of the optimization study which showed a good convergence on the optimum solution The numerical results obtained presented in the paper are going to be validated by a series of model tests in towing tak on the original and optimized hull geometry variants
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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