1,721,006 research outputs found
Identificazione del danno in una struttura intelaiata mediante l'uso di tecniche basate sulle vibrazioni
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Articulated and flexible multibody satellite dynamics modeling
No full textThis paper is concerned with the derivation of the equations of motion for a maneuvering flexible satellite orbiting around the Earth. The structure is assumed to undergo large rigid-body maneuvers and small elastic deformations. The mathematical model is worked out in two levels: in the first one attention is focused on the effects of the rigid dynamics on the flexible motion, while in the second one the reciprocal influence is evaluated. The satellite is provided with flexible solar arrays linked up with the main body with torsional and bending articulations: the mathematical model also considers hinges compliance, when the appendages are blocked in the desired position. Different rotational maneuvers are simulated and numerical results highlight the limitation of the first level modelization, which can be used with confidence for structural analysis, but results inadequate for flight dynamics and control applications. © 2002 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc
DETECTING NONLINEAR BEHAVIOUR USING THE VOLTERRA SERIES TO ASSESS DAMAGE IN BEAM-LIKE STRUCTURES
No full textUsing the example of a cracked cantilever beam, this paper illustrates
a means of identifying damage in structures using the so-called higher
order Frequency Response Function (FRFs) which are based on the Volterra
series. It is well known that, when a beam subject to a dynamic
excitation vibrates, a transverse “breathing”crack present in the beam
can change the state (from open to closed and vice-versa), causing nonlinear
dynamic behaviour. A simple model of a cracked cantilever beam
vibrating in its first mode is proposed. Across the frequency range
which encompasses the first mode of vibration, it is possible to model
the response characteristics of a cracked beam using a relatively simple
asymmetric bilinear oscillator. As described in this article, it is possible
to use these higher order FRFs to characterise the nonlinear behaviour
of the cantilever beam and investigate the qualitative relation with the
parameters of the fault such as entity and location. In this study, the
case of single harmonic excitation has been considered initially. Then,
a new characteristic function, again based on the higher order FRFs, is
proposed for detecting the crack by exploiting the fact that due to the
second-order nonlinear behaviour, two harmonic inputs combine to excite
the sum of their frequencies. Comparisons are made between results
derived using the simple model described and those obtained from a FE
model simulating some experimental tests on the beam
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
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