1,721,116 research outputs found
Anton Powell & Stephen Hodkinson (Ed.), The Shadow of Sparta.
No full textChristien Jacqueline. Anton Powell & Stephen Hodkinson (Ed.), The Shadow of Sparta.. In: L'antiquité classique, Tome 65, 1996. p. 449
Design space dimensionality reduction through physics-based geometry re-parameterization
No full textThe effective control of the extent of the design space is the sine qua non of successful geometry-based optimization. Generous bounds run the risk of including physically and/or geometrically nonsensical regions, where much search time may be wasted, while excessively strict bounds will often exclude potentially promising regions. A related ogre is the pernicious increase in the number of design variables, driven by a desire for geometry flexibility – this can, once again, make design search a prohibitively time-consuming exercise. Here we discuss an instance-based alternative, where the design space is defined in terms of a set of representative bases (design instances), which are then transformed, via a concise, parametric mapping into a new, generic geometry. We demonstrate this approach via the specific example of the design of supercritical wing sections. We construct the mapping on the generic template of the Kulfan class-shape function transformation and we show how patterns in the coefficients of this transformation can be exploited to capture, within the parametric mapping, some of the physics of the design proble
Applications and enhancements of aircraft design optimization techniques
No full textThe aircraft industry has been at the forefront in developing design optimization strategies ever since the advent of high performance computing. Thanks to the large computational resources now available, many new as well as more mature optimization methods have become well established. However, the same cannot be said for other stages along the optimization process - chiefly, and this is where the present thesis seeks to make its first main contribution, at the geometry parameterization stage.The first major part of the thesis is dedicated to the goal of reducing the size of the search space by reducing the dimensionality of existing parameterization schemes, thus improving the effectiveness of search strategies based upon them. Specifically, a refinement to the Kulfan parameterization method is presented, based on using Genetic Programming and a local search within a Baldwinian learning strategy to evolve a set of analytical expressions to replace the standard 'class function' at the basis of the Kulfan method. The method is shown to significantly reduce the number of parameters and improves optimization performance - this is demonstrated using a simple aerodynamic design case study.The second part describes an industrial level case study, combining sophisticated, high fidelity, as well as fast, low fidelity numerical analysis with a complex physical experiment. The objective is the analysis of a topical design question relating to reducing the environmental impact of aviation: what is the optimum layout of an over-the-wing turbofan engine installation designed to enable the airframe to shield near-airport communities on the ground from fan noise. An experiment in an anechoic chamber reveals that a simple half-barrier noise model can be used as a first order approximation to the change of inlet broadband noise shielding by the airframe with engine position, which can be used within design activities. Moreover, the experimental results are condensed into an acoustic shielding performance metric to be used in a Multidisciplinary Design Optimization study, together with drag and engine performance values acquired through CFD. By using surrogate models of these three performance metrics we are able to find a set of non-dominated engine positions comprising a Pareto Front of these objectives. This may give designers of future aircraft an insight into an appropriate engine position above a wing, as well as a template for blending multiple levels of computational analysis with physical experiments into a multidisciplinary design optimization framework
Fan broadband noise shielding for over-wing engines
No full textIncreasingly demanding community noise targets are promoting noise performance ever higher on the list of airliner design drivers. In response, significant noise reductions are being made, though at a declining rate—it appears that a whole airframe approach is now needed to achieve significant further gains. As a possible step in this direction, over-wing engine installations are considered here, which use the airframe itself as a noise shield. The paper is the account of an experimental investigation of the comparative shielding performances of a range of relative engine positions on such a layout. Using the statistical modelling technique Kriging, we build an approximation of the noise shielding metric as a function of the position of the engines above the wing—this can serve as the input to multi-disciplinary design trade-off studies. We then compare the results found with the results of applying simple half-barrier diffraction theory to the same problem. We conclude that the latter could be considered as a first order, conceptual design tool, though it misses certain features of the design merit landscape identified by the experiment presented here
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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