1,721,117 research outputs found
Function space topologies between the uniform topology and the Whitney topology
No full textThis paper, dedicated to new function space topologies between the uniform topology and the Whitney topology also in the setting of the ωμ-metric spaces, splits in two parts. In the former, where X is a Tychonoff space and (Y,d) is a non-discrete metric space, we explore suggestive uniformizable function space topologies on C(X,Y), the set of all continuous functions from X to Y, located between the uniform topology and the Whitney topology. In the Whitney uniformity, whose natural associated topology is the Whitney topology, any continuous function from X to the positive reals gives a measure of closeness between functions in C(X,Y). But, a less stringent and, by the way, efficient uniform control can be performed equally well by limiting, as for example at a first glance, to the measures deriving from all continuous positive functions continuously extendable to a T2-compactification of X. And next, when X is a local proximity space, i.e. densely embedded in a natural T2 local compactification l(X), by limiting to the positive ones in C(l(X),R). We investigate two classes of Tychonoff spaces. That of locally compact ones splittable in two essentially different cases: X hemicompact or not. And, that of spaces densely embedded in a locally compact one. We prove that, whenever X is hemicompact, then any weak Whitney topology relative to a T2-compactification of X agrees with the classical one. Whenever X is locally compact but not hemicompact, then the weak Whitney topology associated with its one-point compactification reduces just to the uniform topology. In the case X is locally compact, paracompact but not hemicompact, thus the free union of an uncountable family of open σ-compact subsets, then, between the uniform topology and the Whitney topology there is a great variety of weak Whitney topologies relative to T2-compactifications of X. Also, whenever X is not locally compact, weak Whitney topologies associated with different T2 local compactifications of X are generally different as is the case if X is the rational Euclidean line. So, weakening the Whitney topology but without renouncing to the uniform convergence, we produce different uniformizable topologies on C(X,Y) related to various significant structures on X. In the latter, since ωμ-metric spaces, where ωμ is an ordinal number, fill a large and attractive class of peculiar uniform spaces containing the usual metric ones, we focus our attention on the ωμ-metric framework. Indeed, we extend the Whitney topology to C(X,Y), where X is again a Tychonoff space but Y is replaced with an ωμ-metric space. Precisely, the range space Y carries a distance ρ:Y×Y→G, sharing the usual formal properties with real metrics but valued in an ordered Abelian additive group G, which admits a strictly decreasing ωμ-sequence converging to zero in the order topology. By a proof strategy essentially based on zero-dimensionality of any ωμ-metric space with μ>0, we achieve, among others, the following result: Whenever X is an ωμ-additive and paracompact space and (Y,ρ,G) is an ωμ-metric space, then the Whitney topology on C(X,Y) is independent of the ωμ-metric ρ. More precisely, the Whitney topology is a topological character as in the classical metric case, μ=0, and X paracompact
SARISTU: Adaptive Trailing Edge Device (ATED) design process review
No full textSARISTU was a big cooperation project granted by the European Commission, 7th Framework Programme, carried out between 2011 and 2015. It dealt with smart aeronautic structures, both morphing and sensored; its main target was to demonstrate the feasibility of designing, manufacturing and operating in representative environment, instrumented structures. Till now, it represents the major effort carried out within the European Union on the development of adaptive architectures for air systems. Inside that big activity, the realization of an Adaptive Trailing Edge Device (ATED) for wing camber adaptations aimed at compensating the weight reduction following the fuel consumption during cruise was addressed. It made the core of investigations target variable geometry aircraft components together with two other analyses concerning the development of shape-changing winglet and droop nose. ATED activities were conducted by the Italian Aerospace Research Centre (CIRA) in tight cooperation with the University of Napoli, “Federico II”, who coordinated a group of 12 different partners from 8 different nations (France, Germany, Greece, the Netherlands, Israel, Spain, Turkey, and Italy). In this paper, an integral synthesis of that work is reported, with a focus on the definition and realization of the components of the presented device. The publication is in fact meant as the first part of a series that is aimed at overviewing the whole adaptive trailing edge development, till wind tunnel tests execution. Such a concise report is a critical and harmonized review of what have been performed by many colleagues spread all over Europe, all of which are duly recalled in the reported bibliography where the reader may access more detailed information and descriptions. In detail, the paper starts with a general introduction of the concept and its aims, to move to the specs definition immediately after. Then, it deals with a short but comprehensive description of the main ATED components: structural skeleton, skin, actuation and sensing systems. It is worth remarking that the paragraph dedicated to the body frame includes some discussion about aeroelastic assessment and manufacture, seen as complementation for a complete assessment of the design constraints
Airfoil Shape Morphing through a Novel Parameterization and Fitting Optimization Method Based on Uniform Non-Rational B-Spline Functions
No full textThe aim of this work is to implement an innovative parameterization and fitting procedure for the definition of a mathematical model useful to describe a wide range of airfoils. They are partitioned into three sections: central box, leading edge, and trailing edge. Each section is mathematically represented by two opposed, uniform, non-rational B-spline curves, describing the upper and lower airfoil segments’ perimeter. A novel approach is used to ensure both the desired continuity between two adjacent segments (up to 2nd derivatives) and sufficient model versatility and flexibility while managing a limited number of parameters, defining tangent and curvature vectors as scale factor variables. These parameters allow for a variable separation approach during the geometric fitting procedure that can be carried out considering two nested optimization processes, one based on a genetic algorithm and the other on a numerical gradient evaluation of the objective function. The representation method has been verified against different airfoils, comparing the geometric and aerodynamic properties of the input and model-based generated profile. To show the mathematical model’s capabilities and possible applications, a comparison between existing and proposed airfoil approximation methods has been provided together with examples of “global” and “local” morphing and CFD analyses of the resulting airfoils
A SMA-based morphing flap: conceptual and advanced design
No full textIn the work at hand, the development of a morphing flap, actuated through shape memory alloy load bearing elements, is described. Moving from aerodynamic specifications, prescribing the morphed shape enhancing the aerodynamic efficiency of the flap, a suitable actuation architecture was identified, able to affect the curvature. Each rib of the flap was split into three elastic elements, namely "cells", connected each others in serial way and providing the bending stiffness to the structure. The edges of each cell are linked to SMA elements, whose contraction induces rotation onto the cell itself with an increase of the local curvature of the flap airfoil. The cells are made of two metallic plates crossing each others to form a characteristic "X" configuration; a good flexibility and an acceptable stress concentration level was obtained non connecting the plates onto the crossing zone. After identifying the main design parameters of the structure (i.e. plates relative angle, thickness and depth, SMA length, cross section and connections to the cell) an optimization was performed, with the scope of enhancing the achievable rotation of the cell, its ability in absorbing the external aerodynamic loads and, at the same time, containing the stress level and the weight. The conceptual scheme of the architecture was then reinterpreted in view of a practical realization of the prototype. Implementation issues (SMA - cells connection and cells relative rotation to compensate the impressed inflection assuring the SMA pre-load) were considered. Through a detailed FE model the prototype morphing performance were investigated in presence of the most severe load condition
Aerospace Science and Technology Vol. 12 , No. 1 . Special Issue on Aircraft Noise Reduction
No full textSelection of 11 Journal articles on the subject of Aircraft Noise Reduction. See website for more informatio
Shape memory alloys for earthquake building protection
No full textUse of Shape Memory Alloys (SMA) is more and more frequent in engineering because of their unique properties of completely recovering the imposed deformations after heating, or automatically returning to the unloaded configuration via a super-elastic process after very large strains (till around 10%). The process is regulated by a phase change in the material, shifting between martensite and austenite. Along this transformation, some SMA change their elastic properties by a factor three and damping coefficient by a magnitude. Super-elastic materials exhibit stable hysteresis loops under cyclic loading and dissipate energy without residual deformation thus providing in perspective self-centering capability for use in buildings earthquake protection. The present study investigates the performance of SMA-based devices for seismic protection of reinforced concrete structures. In countries with high seismic hazard, vulnerability assessment of existing constructions and seismic retrofit implementation is a major challenge for both scientific community and public administration. This paper illustrates seismic retrofit of an existing school building in Italy, using dissipating steel braces. Both SMA-wire dampers and mixed devices combining SMA elements and classical buckling-restrained axial dampers are considered for seismic upgrading. Adopted technique effectiveness and reliability are investigated by comprehensive nonlinear static and dynamic analyses. Numerical results show that super-elastic SMA dampers are effective for mitigating building response to strong earthquakes and providing systems self-centering capability with negligible residual strains
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
A linear guide-based actuation concept for a novel morphing aileron
No full textThis paper deals with the actuation system design of a full-scale morphing aileron for regional aircraft. The aileron is allowed to smoothly change its geometrical configuration and perform the in-flight transition from a baseline shape to a set of optimal morphed ones pre-defined on the basis of aerodynamic requirements. The design of such innovative aileron is aimed not only at substituting the conventional aileron installed on a real aircraft but also to provide additional functionality. The aileron is free to rotate around its main hinge axis and it is also allowed to smoothly modify camber with two independent actuation systems. In such manner it can be used also during cruise with a symmetric deflection between the two half wings in order to reduce drag in off design condition. To accomplish variable aileron shape, a rigid-body mechanism was designed. The proposed aileron architecture is characterised by segmented adaptive ribs rigidly linked each other with spanwise reinforcements such as spars and stringers in a multi-box arrangement. Each rib is split into two movable plates connected by means of rotational hinges in a finger-like mechanism. The mechanism is driven by a load-bearing actuator by means of a kinematic chain opportunely tied based on the structural requirements in terms of shape to be matched and load to be withstood. The proposed device is an innovative arrangement of the quick-return mechanism composed of a beam leverage, commercial linear guides and a crank. The actuator shaft is directly inserted in the crank, which transmits the rotation to the linear guide that slide along a rail moving upward or downward the beam thus resulting in a camber variation. The entire aileron is moved by three leverages internally contained and distributed along the first two bays while the most external ribs are considered passive and their movement slaved. Two actuation layouts are analytically and numerically studied, the analytical theory is presented and validated by means of a multi-body simulation. Moreover, a linear static analysis was carried out under the hypothesis of glued contact between linear guides components simulating a jamming condition. This assumption has been formulated because it represents the most severe condition that envelop all the operative loads to which the actuation system is subjected. The analyses conducted are preliminarily aimed to verify that no failure occur under the imposed loads. In this first design loop, the vertical static force acting on the linear carriage exceeded allowable value and then a new configuration with double-sided linear guides was then investigated
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