1,720,960 research outputs found
High-accuracy methods for frequency-domain flow acoustics
No full textLimited by the current computer memory capacities, it is challenging to solve the convected wave equation in heterogeneous media and at high wave number. This thesis is concerned with the investigation of efficient discretisation methods and solvers for frequency-domain flow acoustics. The application of computational modelling to wave propagation problems is hindered by the dispersion error introduced by the discretisation. Two common strategies to address this issue are to use high-order polynomial shape functions, or to use physics-based methods where the shape functions are local solutions of the problem. Both strategies have been actively developed over the past decades and have demonstrated their benefits compared to conventional finite-element methods, but they have yet to be compared. In this work, a high-order polynomial method and the wave-based discontinuous Galerkin method are compared for two-dimensional Helmholtz problems. A number of different benchmark cases are used to perform a detailed and systematic assessment of the relative merits of these two methods. The results indicate that the differences in performance, accuracy and conditioning are more nuanced than generally assumed. The performance of a method relies heavily on efficient solving procedures for the resulting large, sparse, complex linear systems. An alternative to purely iterative or direct solving procedures is to resort to domain decomposition methods. The Finite Element Tearing and Interconnecting method (FETI-2LM) employs Lagrange multipliers to recover the connections between the non-overlapping sub-domains. An iterative solution procedure is formulated in terms of unknowns defined only on the interfaces between sub-domains. The FETI approaches have been used extensively for Helmholtz problems and their performance is well documented for conventional finite elements. In this work, the FETI-2LM formulation is extended to the linearised potential theory for sound waves propagating in a potential base flow. In each sub-domain, a high-order finite element method is used to solve the governing equations. The proposed approach is validated on a number of two-dimensional test cases. In addition to the dependency on the mesh size, frequency, or number of subdomains, the influence of the interpolation order and Mach number on the scalability of the method is also assessed. The memory requirements for solving a simple three-dimensional problem is also evaluated and compared to that of a direct solver. Finally, the proposed method is applied to the problem of propagation of fan noise from the inlet of an engine, considering a realistic three-dimensional geometry and flow field
A comparison of high-order polynomial and wave-based methods for Helmholtz problems
No full textThe application of computational modelling to wave propagation problems is hindered by the dispersion error introduced by the discretisation. Two common strategies to address this issue are to use high-order polynomial shape functions (e.g. hp-FEM), or to use physics-based, or Trefftz, methods where the shape functions are local solutions of the problem (typically plane waves). Both strategies have been actively developed over the past decades and both have demonstrated their benefits compared to conventional finite-element methods, but they have yet to be compared. In this paper a high-order polynomial method (p-FEM with Lobatto polynomials) and the wave-based discontinuous Galerkin method are compared for two-dimensional Helmholtz problems. A number of different benchmark problems are used to perform a detailed and systematic assessment of the relative merits of these two methods in terms of interpolation properties, performance and conditioning. It is generally assumed that a wave-based method naturally provides better accuracy compared to polynomial methods since the plane waves or Bessel functions used in these methods are exact solutions of the Helmholtz equation. Results indicate that this expectation does not necessarily translate into a clear benefit, and that the differences in performance, accuracy and conditioning are more nuanced than generally assumed. The high-order polynomial method can in fact deliver comparable, and in some cases superior, performance compared to the wave-based DGM. In addition to benchmarking the intrinsic computational performance of these methods, a number of practical issues associated with realistic applications are also discussed
A performance study of high-order finite elements and wave-based discontinuous Galerkin methods for a convected Helmholtz problem
No full text
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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