1,720,962 research outputs found
Experimental measurement of the nearfield longitudinal wake profiles of a high-speed prismatic planing hull
No full textThis study details an extensive investigation into the nearfield longitudinal wake profiles of a high-speed planing hull. Developing understanding this flow is benaficial to the designers of stepped hulls in determining how the forebody’s wake intersects with the afterbody. As no experimental data was available, a novel small-scale model-testing programme was undertaken, measuring Centreline (CL) and Quarter Beam (QB) nearfield longitudinal wake profiles, as well as the forces. The nearfield wake profile was found to exhibit trends in agreement with the findings of studies investigating the mid and far-field wake. The results of this experimental work are provided in full as validation data. Savitsky’s Wake Equations and the Linear Wake Assumption are then assessed to determine the level of confidence with which they may be used to model this flow. Savitsky’s Wake Equations displayed a surprising level of accuracy whereas the Linear Wake Assumption was invalid for the conditions investigated
Strategies to minimise numerical ventilation in CFD simulations of high-speed planing hulls
No full textNumerical Ventilation is a well-known problem that occurs when the Volume of Fluid method is used to model vessels with a bow that creates a small, acute entrance angle with the freesurface, typical for planing hulls and yachts. There is a general lack of discussion focusing upon Numerical Ventilation available within the public domain, which is attributable to the fact that it only affects such a niche area. The information available s difficult to find, often fleetingly mentioned in papers with a different focus. Numerical Ventilation may be considered one of the main sources of error in numerical simulations of planing hulls and as such warrants an in-depth analysis. This paper sets out to bring together the available work, as well as performing its own investigation into the problem to develop a better understanding of Numerical Ventilation and present alternate solutions. Additionally, the success and impact of different approaches is presented in an attempt to help other researchers avoid and correct for Numerical Ventilation. Interface smearing caused by the simulations inability to track the freesurface is identified as the main source of Numerical Ventilation. This originates from the interface between the volume mesh and the prism layer mesh. This study looks into the interface to identify strategies that minimise Numerical Ventilation, presenting a novel solution to prism layer meshing that was found to have a positive impact. Through the implementation of a modified High Resolution Interface Capture (HRIC) scheme and the correct mesh refinements, it is possible to minimise the impact of Numerical Ventilation to a level that will not affect the results of a simulation and is acceptable for engineering applications<br/
Numerical modelling of the nearfield longitudinal wake profiles of a high-speed prismatic planing hull
No full textThis study investigates the level of accuracy with which Computational Fluid Dynamics (CFD) is capable of modelling the nearfield longitudinal wake profiles of a high-speed planing hull. It also looks to establish how various set-ups influence the accuracy, with a specific emphasis on turbulence modelling. It analyses a hull over a broad range of conditions to provide detailed insight into the strengths and limitations of CFD, comparing the numerical results to the experimental results previously generated by the authors. A quantitative comparison is made for the centreline (CL) and quarterbeam (QB) longitudinal wake profile plots. Following this, a qualitative comparison is made between photos of the flow pattern from the experimental testing and free surface elevation plots from CFD. The study concluded that CFD is an accurate and robust method of modelling the nearfield longitudinal wake profiles of a high-speed planning hull.</p
Minimizing numerical ventilation in computational fluid dynamics simulations of high-speed planing hulls
No full textNumerical ventilation (NV) is a well-known problem that occurs when the volume of fluid method is used to model vessels with a bow that creates an acute entrance angle with the free surface, as is typical for both planing hulls and yachts. Numerical ventilation may be considered one of the main sources of error in numerical simulations of planning hulls and as such warrants an in-depth analysis. This paper sets out to bring together the available work, as well as performing its own investigation into the problem to develop a better understanding of numerical ventilation and present alternate solutions. Additionally, the success and impact of different approaches are presented in an attempt to help other researchers avoid and correct for numerical ventilation. Interface smearing caused by the simulation being unable to track the free surface is identified as the main source of numerical ventilation. This originates from the interface between the volume mesh and the prism layer mesh. This study investigates this interface, presenting a novel solution to prism layer meshing that was found to minimize numerical ventilation. Through the implementation of a modified high-resolution interface capture (HRIC) scheme and the correct mesh refinements, it is possible to minimize the impact of numerical ventilation to a level that will not affect the results of a simulation and is acceptable for engineering applications.</p
Improving the hydrodynamic performance of stepped hulls through enhanced analysis techniques
No full textThe inclusion of steps presents an attractive solution to improving the efficiency of high-speed planing vessels, yet analysis tools and the available knowledge for improving stepped hulls are considerably under-developed. The research presented in this thesis addresses these issues, seeking answers to the question: “How can we enhance and accelerate analysis techniques for stepped hulls through knowledge developed from numerical simulations and can hydrodynamic performance be improved through the application of these tools.”The studies in this thesis apply state-of-the-art Fluid Dynamics (CFD) to examine the impact that the addition of steps has to a planning hull, investigating the mechanisms through which efficiency is improved. The fluid flow is analysed as it separates at each step and interacts with the remainder of the hull, with existing methods of modelling this behaviour being evaluated and novel modelling strategies being proposed.The knowledge established through these investigations is applied to develop mathematical models for the performance prediction of single and double-stepped planing hulls, aiming to address the limitations and enhance the accuracy of those currently available. The proposed models displayed high degrees of accuracy, calculated the resistance with an average error of 2.50% and 1.29% respectively for single and double stepped hulls.The enhanced analysis techniques are applied to investigate how the hydrodynamic performance of single and double stepped hulls may be improved. This was successfully achieved, identifying design trends and establishing relationships between design parameters that may be universally applied by designers to lower the resistance of stepped hulls.The inclusion of steps presents an attractive solution to improving the efficiency of high-speed planing vessels, yet analysis tools and the available knowledge for improving stepped hulls are considerably under-developed. The research presented in this thesis addresses these issues, seeking answers to the question: “How can we enhance and accelerate analysis techniques for stepped hulls through knowledge developed from numerical simulations and can hydrodynamic performance be improved through the application of these tools.”The studies in this thesis apply state-of-the-art Fluid Dynamics (CFD) to examine the impact that the addition of steps has to a planning hull, investigating the mechanisms through which efficiency is improved. The fluid flow is analysed as it separates at each step and interacts with the remainder of the hull, with existing methods of modelling this behaviour being evaluated and novel modelling strategies being proposed.The knowledge established through these investigations is applied to develop mathematical models for the performance prediction of single and double-stepped planing hulls, aiming to address the limitations and enhance the accuracy of those currently available. The proposed models displayed high degrees of accuracy, calculated the resistance with an average error of 2.50% and 1.29% respectively for single and double stepped hulls.The enhanced analysis techniques are applied to investigate how the hydrodynamic performance of single and double stepped hulls may be improved. This was successfully achieved, identifying design trends and establishing relationships between design parameters that may be universally applied by designers to lower the resistance of stepped hulls
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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