1,720,993 research outputs found
Impact of hull propeller rudder interaction on ship powering assessment
No full textIt is the complex flow at the stern of a ship that controls the overall propulsive efficiency of the hull-propeller-rudder system. This work investigates the different analysis methodologies that can be applied for computing hull-propeller-rudder interaction. The sensitivity into which the interaction between the propeller and rudder downstream of a skeg is resolved as well as varying the length of the upstream skeg are also discussed including techniques to consider in such computations. Throughout the work, the importance of hull-propeller-rudder interaction for propulsive power enhancement is demonstrated. A final case study examines the performance of a twin skeg, twin screw arrangement
Experimental investigation of the influence of floodwater due to ship grounding on motions and global loads
Get PDFHigh profile collision and grounding incidents show that safety standards for ships need improvement to ensure ship survivability and reduce the potential for loss of life. An experimental investigation into the influence of floodwater, and transient flooding on the motions and structural response of a ship hull following a grounding incident is presented. Results show that floodwater can have a significant effect on the magnitude of ship responses; testing of the transient flooding case provides the opportunity to quantify the magnitude of these changes as well as the time to flood by provision of intact and flooded data during a single test. The movement of the floodwater free surface shows some substantial second order sloshing effects when close to the ship peak response, but little movement in higher frequency waves. Comparisons to classification design rules indicate that there is scope for further assessment of safety margins, including investigation of global responses in conjunction with any local loading due to the presence of floodwater. Future work will look at improving the modelling of the floodwater free surface and carrying out further transient flooding testing in order to better quantify the effect of a ship grounding incident on the survivability of a vessel
Evaluation of terrain collision risks for flight style autonomous underwater vehicles
No full textPhotographic surveys of the seafloor with flight style autonomous underwater vehicles are a very effective tool for discovery and exploration. Due to the high terrain collision risk for the survey vehicle, they are employed with caution. The extent of this risk remains unquantified. For mission planning, researchers and vehicle operators have to rely on their experience.This paper introduces measures for vehicle risk and success and analyses how previously mapped terrains and artificially generated terrain maps can be used to categorize terrains. The developed measures are applied to a simulation of the Autosub6000 flight style AUV terrain following system. Based on quantitative parameters, changes to the obstacle avoidance system and survey mission plans can be better informed
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
Design, modelling and simulation of a hybrid fuel cell propulsion system for a domestic ferry
No full textDispelling 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
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