1,720,958 research outputs found
A New Semi-Active Tensairity Structure Equipped With Shape Memory Cables: Experiments And Computations.
No full textThe concept of tensairity structure is interesting for numerous applications in several application fields according to the low ratio between self-weight and its loading capacity. The basic components of a tensairity are represented by a cylindrical pneumatic/inflatable element, a couple of cables wrapped around and attached to a slender beam positioned along the generatrix of the cylinder. When the tensairity is loaded, the beam is compressed while the cables are subject to tension thus realizing a very efficient structure. However, one of the main limitations for dynamic applications is due to the low damping ratio which makes the structure susceptible of continuous vibrations. This study explores a new concept of semi-active tensairity that provides a solution to this loss of performance. A reduced-scale prototype has been manufactured according to the tensairity concept in U.S. Patent No. 10,407,939. The main innovations are represented by the employment of NiTiNOL wires wrapped around the pneumatic element, the introduction of manual and automatic tensioning systems at the ends of the slender beams and the adoption of a design that provides the capability of sustaining loads in any direction. The load-displacement curves have been acquired with a MTS testing machine for the tensairity equipped with NiTiNOL and steel wires, respectively, and for different pretension levels. Dynamic experiments have been performed to measure the resonance frequencies of the lowest few modes as a function of the pretension levels. The results demonstrate the higher dissipation capacity of the tensairity equipped with shape memory wires whose tensions are semi-actively controlled. Finally, a nonlinear FEM model has been implemented in ABAQUS and parametrized in Python to simulate the static and dynamic tests
Nonlinear Normal Modes For Damage Detection: Theoretical Concepts And Preliminary Experimental Validation
No full textThe exploitation of nonlinearities in the eld of damage detection is a promising direction towards robust and reliable monitoring systems for engineering applications. In this perspective, the concept of nonlinear normal mode (NNM) is a natural candidate for extending the knowledge already established in the linear framework and for developing new approaches. A clamped-clamped beam with localized cross-sectional reductions across the beam span is considered. The problem is first analytically tackled via the method of multiple scales for computing the
NNMs and the backbone curves. The latter describes the dependence of the resonance frequencies on the oscillation amplitude and are governed by the so-called effective nonlinearity coefficient for each mode. Subsequently, an experimental campaign is carried out considering an undamaged and a damaged beam to validate the analytical results. The effective nonlinearity coeffcient is shown to exhibit a sensitivity to damage higher than that exhibited by the linear natural frequencies, whereas the backbones associated to each mode reveal an interesting dependence
on the sti ness reduction and damage location
Nonlinear Normal Modes For Damage Detection: Analytical Results and Experiments
No full textThe use of nonlinearities in damage detection is a potential avenue for developing accurate monitoring systems in a variety of engineering applications. In several situations the linear theory reveals its drawbacks, for example, when environmental disturbances affect the structural response. For instance, the thermal effects can induce frequency shifts of the same order of magnitude of the damage itself [1] and, for properly accounting them, accurate nonlinear models become necessary [2]. In this prospective, it is interesting to ascertain if the nonlinear response is more sensitive to damage than the linear one. The nonlinear normal modes concept (NNMs) lends itself naturally to extend the consolidated knowledge of the linear theory [3]. The sensitivity of the nonlinear dynamic response to damage is investigated considering a straight beam clamped at both ends with localized reductions of the cross-sectional area in different positions along the beam span. In the first stage, the problem is analytically tackled with the method of multiple scales for computing the NNMs and the backbones curves. The trends of the effective nonlinearity coefficient for the lowest bending mode as function of the damage position and severity are obtained and compared with those of the linear frequencies. In the second stage, an experimental campaign is carried out on a set of steel beams with different levels of area reduction within a few segments along the beam span. The analytical results are qualitatively corroborated by tailored experiments confirming the important role that the nonlinear structural response can play towards damage detection
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
A Multi-Bandgap Metamaterial With Multi-Frequency Resonators
No full textA 2D metamaterial cellular system inspired by lightweight honeycombs and spider webs is investigated. The hexagonal cells of the honeycomb act as hosting substructures for spider-web-like or cantilever resonators with added lumped masses which can vibrate, in principle, in any of the infinitely many modes. Contrary to traditional approaches utilizing discrete mass-spring resonators, here the infinite-dimensional (full spectrum) resonators are intentionally tailored to generate multiple, complete or incomplete, stop bands across which wave propagation is either totally or partially suppressed along preferential directions. The Plane Wave Expansion method is employed to obtain the dispersion curves and the bandgap sensitivity with respect to the design parameters. Experimental results based on laser scanning vibrometry corroborate the theoretical predictions and confirm the robustness of the stop band behavior with a wealth of results which pave the way towards suitable optimization strategies and a closer understanding of these formidable stop band cellular material systems
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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