1,720,974 research outputs found
Coupling an inviscid IGA – BEM solver with X-Foil's boundary-layer model for 2D flows
Full text linkIn this work we couple an IGA-BEM solver for 2D lifting flows with the viscous model in X-Foil [1], a vintage but still widely used software tool for the design and analysis of subsonic airfoils, towards deeper integration of the isogeometric concept in 2D flow models that incorporate boundary-layer corrections. The formulation of the exterior potential-flow problem reduces to a Boundary Integral Equation (BIE) for the associated velocity potential. Adopting the approach presented in [3], the resulting BIE is handled by an IGA-BEM method, combining: (i) A generic B-splines parametric modeler for generating hydrofoil shapes, using a set of 8 design-oriented parameters; (ii) The very same basis of the geometric representation for representing the velocity potential, and (iii) Collocation at the Greville abscissas of the knot vector of the hydrofoil’s B-splines representation, appropriately enhanced to accommodate the null-pressure jump Kutta condition at the trailing edge. For the viscous part of the solution, the two-equation model of X-Foil [2] is employed. X-Foil’s inviscid solver is “circumvented” and inviscid isogeometric parameters are sent to its viscous component, namely the integral momentum and kinetic energy shape parameter equations presented in [2]. The derived coupled system is tested for NACA4412 and NACA0012 airfoils and the output lift and drag coefficients for different angle of attacks are compared to experimental data, uncoupled X-Foil results and one-way coupling results obtained [4] via the software tool PABLO [5]. The so-resulting coupled system can be used in airfoil/hydrofoil shape optimisation algorithms with a variety of optimisation criteria such as maximum lift coefficient, maximum lift-over-drag-ratio, minimum deviation of the airfoil/hydrofoil area from a reference area, etc. REFERENCES [1] Drela, M. (1989) “XFOIL: An analysis and design system for low Reynolds number airfoils”, MIT, Massachusetts, USA. [2] Drela, M., Giles, M. (1987) “Viscous – inviscid analysis of transonic and low Reynolds number airfoils”, AIAA Journal, vol. 25(10), pp. 1347 – 1355. [3] Kostas, K.V., Ginnis, A.I., Politis, C.G., Kaklis, P.D. (2017) “Shape-optimization of 2D hydrofoils using an Isogeometric BEM solver”, Computer Aided Design, vol. 82, pp. 79-87. [4] Kostas, K.V., Ginnis, A.-A.I, Politis, C.G., Kaklis P.D. (2017) “Shape-optimization of 2D hydrofoils using one-way coupling of an IGA-BEM solver with a boundary-layer model”, Coupled Problems 2017, VII International Conference on Coupled Problems in Science and Engineering, June 12-14, 2017, Rhodes (GR)
Marine-Design Education
No full textThis report addresses Marine-Design Education in view of present and forecasted demands of the maritime industry, determined by a drastically transforming economic and technological maritime environment. In this framework, this report discusses in depth IT-based Marine Design education (par. 4) and reveals innovative educational concepts and initiatives, such as the EiT (Experts in a Team) concept (par. 3), the SFS (Student Friendly Software) initiative (par. 5), Education Driven Research (EDR, par. 6) and Research Based Education (RBE, par. 6). Nevertheless, the paper stresses the need for continuity between traditional and modern ways of teaching (par. 4) and points out that Marine Design education is not only about Design, but should also address project/business administration and decision making issues (par. 7)
Editorial : special issue on: parametric CAD modeling for Naval Architecture, Ocean & Marine Engineering (NAOME)
Full text linkThe motivating aim of the present Special Issue (SI) is to attract the interest of researchers who are active in the area of Parametric Modeling (PM) for Naval Architecture, Ocean & Marine Engineering (NAOME) and project it onto the broader reader audience of Ocean Engineering (OE), Elsevier, through a number of carefully reviewed papers. We strongly believe that, as the need of the NAOME industrial and academic communities for optimising complex shapes increases persistently, the availability of efficient and robust parametric modelers of the involved geometric environments will be an increasingly important factor for successful designs and constructions
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
IGA-BEM for lifting flows
Full text linkCombining Iso-Geometric analysis (IGA) with Boundary Element Methods (BEM) for inviscid lifting flows imposes a number of difficulties. Firstly, an IGABEM collocation scheme has to take into account the tangent-plane discontinuity occurring along the trailing edge (TE). More important, the scheme has to handle the non-linear Kutta condition, securing continuity of the normal velocity and pressure through the a-priori unknown wake, a force-free boundary surface emanating from TE. In this presentation we shall review the status of our work towards developing a pair of IGABEM collocation schemes for computing steady lifting flows around 2D and 3D bodies , e.g., hydrofoils, marine propellers; [1,2]. In the latter case, the ansatz functions are inherited from T-spline representations which are free from singularities occurring, e.g., at the tip of a propeller blade, when NURBS are used. REFERENCES [1] Kostas, K.V., Ginnis, A.-A. I., Politis, C.G., Kaklis, P.D, “Shape-optimization of 2D hydrofoils using an Isogeometric BEM solver”, Computer-Aided Design, vol. 82, pp. 79-87, (2017). [2] Chouliaras, S.P., Kaklis, P.D., Ginnis, A.-A.I., Kostas, K.V., Politis, C.G., “An IGA-BEM method for the open-water marine propeller flow problem”, International Conference on Isogeometric Analysis, Pavia (IT), 11-13 September 2017
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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