1,720,964 research outputs found
Global wave-induced loads in abnormal waves: comparison between experimental results and classification society rules
No full textIt is important to assess the consequences of ship encounters with abnormal waves due to the perceived dangers of such encounters. A starting point for this is the assessment of global loads, with a focus on examining how the design rules fare with respect to loads induced by abnormal wave encounters. This paper presents the results of an experimental investigation into the global wave induced loads experienced in a range of abnormal sea states. Results are obtained for a segmented, flexible backbone model of a typical naval frigate. Abnormal wave encounters result in a significant increase in the global wave-induced loads compared to the equivalent random sea, with slamming becoming considerably more severe. Through comparisons with the experimental measurements it is concluded that the design rules which allow for an extreme wave encounter provide a reasonable safety margin for the global loads in abnormal waves, although discrepancies occur towards the aft of the vessel. Further investigation of the amount and conditions in which the design rules may be exceeded by an abnormal wave encounter is require
The influence of forward speed on ship motions in abnormal waves: experimental measurements and numerical predictions
No full textShip encounters with abnormal waves are increasingly well documented and it is therefore important to be able to model such encounters in order to assess the risks involved and whether there is a requirement for more stringent design rules.This paper presents the results of an experimental investigation into the influence of abnormal waves on a vessel travelling with forward speed in irregular seas. The vessel studied in this case is a naval frigate travelling at a range of speeds. To put the motions measured in abnormal waves into context comparisons are made to those in random seas with a variety of significant wave heights, both non-severe and severe. A further objective is to compare experimental measurements with motion predictions from both a two-dimensional linear strip theory and a three-dimensional partly nonlinear seakeeping model.Results demonstrate that abnormal waves may not necessarily be the worst conditions that a ship can encounter. However, accelerations derived from the rigid body motions appear to be in excess of rules values. This has implications for design due to the unexpected nature of abnormal wave occurrence and the consequent likelihood of encountering such a wave at a higher speed (hence in a more severe operating condition) than a random sea of an equivalent height.The three-dimensional partly nonlinear model demonstrates improved agreement with experimental measurements of rigid body motions, compared to the two-dimensional strip theory. It is therefore considered to have greater potential as a design tool for abnormal wave encounters. Further validation with a wide range of sea states and vessel types is required.<br/
A comparison of abnormal wave generation techniques for experimental modelling of abnormal wave-vessel interactions
No full textThe ability to model abnormal waves in an accurate and repeatable manner is important in order to achieve the objective of assessing vessel response in such conditions.Although techniques for the practical generation of abnormal waves are readily available in literature, no comparison of their suitability to modelling abnormal waves experimentally is available. The purpose of this paper is to provide such a comparison. Identified techniques are the NewWave, constrained NewWave and optimised sea, all based on sea spectra. A particular focus is the usefulness of each technique for modelling a travelling vessel encountering an abnormal wave. Experimental results are presented for each model compared to linear and second order wave theories, and the quality of results is assessed using an uncertainty analysis. Results demonstrate the constrained NewWave is highly repeatable, but suffers from discrepancies in the time domain when compared to predicted profiles. In order to generate a known wave profile, the NewWave or optimisation techniques appear the most suitable. Of these, NewWave should be used if only the local (abnormal) wave profile is required. To model a realistic scenario including the response history of a vessel, the optimised sea should be applied.<br/
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
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The deep sea energy park: harvesting hydrothermal energy for seabed exploration
No full textModern society is in growing need of natural resources. Energy security remains one of the greatest challenges that we face. We need increasing amounts of energy, but it is no longer acceptable to supply it at the expense of the environment. In the coming years we will continue our struggle to innovate and discover new sources of clean, cheap and reliable energy. The ocean has vast resources that could contribute to solving our energy needs.The evolution of the energy market in the coming 50 years requires innovation, strong international cooperation and moderation from consumers. This volume in The LRET collection on seabed exploitation will explore some opportunities of meeting these challenges. The seabed, defined here as the bottom of the ocean, has rich natural reserves including energy, solid minerals, and biogenic resources. Using a scenario planning approach, we determine that energy exploitation from the seabed has the greatest short- and long-term potential.This volume explores the technological challenges in exploiting the seabed as a source of energy. We show two scenarios exploring an evolution-based strategy for maturing technology needed in seabed energy exploitation. The first is a conservative scenario that imagines the business as usual outcome towards greenhouse gas emissions policy. In this outcome, we imagine the growth of energy technology in ocean research, exploration and prospection. The second scenario explores the outcome of an aggressive policy and integration outcome, reflecting the IEA 450 Scenario. In this outcome, the growth of seabed energy technology derives from offshore geothermal or hydrothermal energy.Finally, this volume shows the design of a novel application for power generation from the seabed. The system is an Autonomous Observation Node, designed for ocean research, exploration and prospection. Our novel approach for collecting power from the hydrothermal vent fields implements thermoelectric generators. We show preliminary design options, either tapping a temperature gradient directly from the plumes of a hydrothermal vent, or using high-pressure thermosyphons installed in a well on the hydrothermal mounds. These alternatives can provide clean and reliable power with less environmental impact on the surrounding ecosystem. The system design shown in this volume considers the most conservative scenario of growth for energy in the seabed exploitation industry.We leave the reader with some thoughts. Although the ocean covers approximately 71% of our planet, much of its reserves are yet undiscovered. Any prospect of resource exploitation remains limited by our lack of understanding of the fundamental processes that shape and transform the ocean. Therefore, we need affordable and reliable technology to facilitate long-term scientific observation and exploration of the ocean
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
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