1,720,986 research outputs found
Vibration of thin-walled laminated composite beams having open and closed sections
No full textAn efficient technique based on one dimensional beam finite element analysis for vibration of thin-walled laminated composite beams having open and closed sections is proposed in this paper. The developed technique is quite generic which can accommodate any stacking sequence of individual walls and considers all possible couplings between different modes of deformation. The formulation has accommodated the effect of transverse shear deformation of walls as well as out of plane warping of the beam section where the warping can be restrained or released. The inclusion of shear deformation has imposed a problem in the finite element formulation of the beam which is solved successfully utilising a concept developed by one of the authors. A number of numerical examples of open section (I and C sections) beams and closed section box beams are solved by the proposed technique and the results predicted by the proposed model are compared with those obtained from literature as well as detailed finite element analysis using a commercial code. The results show a very good performance of the proposed modelling technique
An efficient beam element for the analysis of laminated composite beams of thin-walled open and closed cross sections
Full text linkA condensed fully coupled beam element for thin-walled laminated composite beams having open or closed cross sections is presented. An analytical technique is used to derive the cross-sectional stiffness of the beam in a systematic manner considering all the deformation effects and their mutual couplings. An efficient finite element approximation is adopted for the transverse shear deformation, which has helped to conveniently implement the C1 continuous formulation required by the torsional deformation due to incorporation of warping deformation. The performance of the element is tested through the solution of numerical examples involving open section I and channel (C) beams and closed section box beams under different loading conditions, and the obtained results are compared with model as well as experimental results available in literature.<br/
Development Of The Helmholtz Solver Based On A Shifted Laplace Preconditioner And A Multigrid Deflation Technique
No full textThe Helmholtz equation is the simplest possible model for the wave propagation. Perhaps this is the reason, despite denying traditional iterative methods like Krylov sub-space methods, Multigrids, etcetera, numerical solution of the Helmholtz equation has been an interesting and abundant problem to researchers since years. The work in this dissertation is also classified as an attempt to develop fast and robust iterative methods for the solution of the Helmholtz equation. This works is specified for applications in seismic imaging-Geophysics, where usually high frequency are used. Thus we will be targeting large wavenumber Helmholtz problems. The finite difference discretization of the Helmholtz equation with typically given Absorbing (Sommerfeld) boundary conditions gives rise to symmetric, non-Hermitian, indefinite linear systems. Resolution of large wavenumber requires larger number of grid points, thus large linear systems. Many (sparse) direct solvers and hybrid (direct and iterative) solvers have been proposed, but it is quite obvious for very large problems that (sparse) direct solvers have been too much depending upon memory, which makes them less acceptable. Quite a lot of work has been invested in researching iterative solution methods for the Helmholtz equation since many decades. The indefiniteness, which increases with respect to an increase in the wavenumber, poses extra problems for iterative solvers and robust solution of indefinite (large) linear system forms an important research activity. Many iterative techniques like domain decomposition methods, multigrid methods and preconditioners for Krylov subspace methods have been proposed but non of them has been quite robust. For multigrid methods, indefiniteness arises difficulties in having both good smoothing property and constructing appropriate coarse-grid approximations of the problem, which are responsible for further reduction of low frequency errors. Many attempts have been spent in algebraic variants of multigrid methods. Some of them works well with limitation of homogeneity. Most of them fails to show satisfactory convergence. The same holds for Krylov subspace methods. One of the difficulties for Krylov methods is to find a cheap and performing preconditioner for the indefinite Helmholtz equation. An overview of preconditioners, ranging from classical to matrix based, for indefinite Helmholtz linear system has been give in this thesis. A matrix-based complex shifted Laplace preconditioner (CSLP) has been seen as best in the available ones. However, with increasing wavenumbers CSLP shows a slow convergence behavior. We address this issue continuing using CSLP while taking care of its requirement of specific complex shifts. The projection-type preconditioners have been widely investigated by researchers in numerical analysis community. We propose the projection-type deflation preconditioner to tackle the near-singular nodes, which are the cause of the decay the convergence of, this otherwise well performing, CSLP. Like multigrid, this deflation pre-conditioner, named as ADEF1, requires to solve coarse problems at different coarser levels. An optimized algorithm has been tested and proposed suggesting iterative solution of coarse problems at different levels. This finalizes as a multilevel preconditioner. The re-discretization coarsening strategy that we propose and investigate in this thesis is aimed at reducing the memory size and maintaining stencil size. The multilevel Krylov method (MLKM) has also been investigated and compared with its counterpart ADEF1. The rigorous Fourier analysis (RFA) to investigate the convergence of iterative methods forms a separate research theme, which is included in the thesis. We analyse the proposed multilevel preconditioners ADEF1 and MLKM for two-levels. Analysis shows spectral behavior of the preconditioner, which can be taken as favorable for Krylov methods. RFA points out near-singular modes and highlights their contribution in prevailing stagnation. Further the convergence can be enhanced by adapting coarse grid operator at different levels. The proposed preconditioners have been tested on academic as well as the bench mark Marmousi problem. A huge reduction in number of iterations can be noticed. A comparison in the amount of iterations and solve time, specially for three-dimensional problem, shows that the invested work has paid-off. Proposed preconditioners has been uniformly performing for one- to three-dimensions as well as for heterogeneous medium problems.Applied mathematicsElectrical Engineering, Mathematics and Computer Scienc
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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