1,720,982 research outputs found
Topology optimization of masonry blocks with enhanced thermomechanical performances
Full text linkTopology optimization is employed to define the geometry of the cross-section of any masonry block that minimizes its thermal transmittance, with the aim of maximizing the thermal insulation of masonry buildings. Constraints on the mechanical properties of the block are also prescribed. The effect of the design constraints on the optimal layout of the blocks is investigated. The thermal efficiency of the optimized units is also compared with that of commercially available blocks
Mixed finite-elements for eigenvalue optimization of incompressible media
No full textAn alternative formulation for the eigenvalue optimization of structures made of rubber- like material is presented. The proposed methodology adopts the truly-mixed variational formulation that descends from the principle of Hellinger-Reissner. This formulation has regular stresses as main variables and discontinues displacements that play the role of lagrangian multipliers. The use of this discretization passes the inf-sup condition [1] even for incompressible materials and therefore allows to overcome the arising of the locking phenomenon, difficulty often found handling rubber material in displacement-based finite element contexts. The approach presented in the work consists in the adoption of a mixed-FEM bidimensional discretization that uses the composite element of Johnson and Mercier [2] as to the discretization of the stress field. Also this discrete formulation, as the continuous one, meets automatically the Babuska-Brezzi conditions of the problem even in presence of incompressible materials. Within this mixed framework, the work addresses classical eigenvalue optimization problems, with the aim of maximizing the first eigenfrequency or a weighted sum of the first eigenvalues, given the domain and a volume constraint [7] , [3]. For all the problems used to test the methodology, MMA [4] is chosen as minimization algorithm, within an optimization framework relying on SIMP method. Peculiar attention is devoted to the problem of the arising of localized modes and to the difficulties in getting pure 0-1 designs in plane strain conditions
Reinforced concrete seismically-excited frame design with a new mixed H2/H∞ optimization approach
No full textA new approach is proposed for the optimal design of seismically excited reinforced concrete frames. Unlike most existing methods that do not exploit the input/output relationship between the base acceleration and the structural response, the main feature of the presented approach is to directly shape the input/output transfer function so as to reduce the dynamic amplification factors that govern the structural response. The approach is general with respect to distinctive issues: on the one side the structural output may encompass different quantities of engineering interest such as the overall compliance, the lateral displacement of a representative point (typically the averaged top-storey displacement) and the interstorey drift vector, on the other two system norms may be considered (or a combination thereof) as to the transfer-function amplitude to be minimized, namely the (Formula presented.)-norm and the (Formula presented.)-norm. The former allows to reduce the peak-gain response whereas the latter the squared power energy of the response. By cleverly combining the two, typically by means of a convex combination, one may end up with significant peak gain as well as power response reduction. A numerical investigation on a 2D frame is conducted to validate the theoretical framework that is modeled following Eurocode 8 (CEN in Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings. European Standard EN 1998-1, Brussels (2004)) in medium ductility class (DCM) but the method applies to any regulations including modern displacement based codes such as the fib Model Code 2010 (Bulletins Nos. 65/66, Federation Internationale du Beton, Lausanne 2012
On maximum stiffness of orthotropic shells
No full textAssuming the specific elastic strain energy as a meaningful measure of the stiffness/flexibility of a structural element, in this paper orthotropic shell structures of general shape will be considered and extreme values of the stored strain energy density sought. The role of design variable will be played by the local orientation of the principal directions of orthotropy with respect to a given reference frame, defined on the mid-surface of the shell. Assuming the strain field as prescribed, the optimization problem will be formulated in variational form as a min max problem and the necessary condition for stationarity will be obtained as well. Special features of such optimality condition will be discussed and the analogies with similar problems in plane elasticity pointed out
Mixed finite-element approaches for topology optimization
No full textWe present a novel topology optimization formulation capable to handle the presence of stress constraints. The main idea is to adopt a mixed finite-element discretization scheme wherein not only displacements (as usual) but also stresses are the variables entering the formulation. By so doing, any stress constraint may be directly handled within the optimization procedure. Hellinger-Reissner variational principles are derived in continuous and discrete form that are included in a rather general topology optimization problem in the presence of stress constraints that is solved by the method of moving asymptotes (MMA) [21]. A novel relaxation approach is proposed to handle the non-qualification properties of the stress constraints
A mixed approach to cohesive crack propagation
No full textA mixed variational formulation with discontinuous displacements and continuous tractions is proposed for the analysis of cohesive-crack propagation in elastic media. Such a formulation gives rise to a peculiar finite-element discretization scheme that is based on the Johnson-Mercier composite elements as to the stresses. Numerical results concerning classical benchmark problems are proposed and need for future developments highlighted, including the analysis of elastic-plastic and incompressible media
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
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