1,720,972 research outputs found
Dynamic Identification of a Solid Rocket Motor From Firing Test Using Operational Modal Analysis
No full textThe main objective of this paper is the identification of the dynamic properties of a solid rocket motor using data recorded during a firing test, characterized by a mass variation due to the burning propeller. The dynamic identification of the motor is provided by applying Operational Modal Analysis (OMA) methodologies able to estimate the modal parameters of the structure undergoing its operative conditions. The sensitivity of the OMA approaches to deal with structures characterized by time-dependent parameters is evaluated through a numerical simulation. Moreover, a comparison between the estimates from different state-of-the-art approaches in OMA (operating in both time and frequency domain) are provided. The capabilities of the OMA methods to track the changes in the natural frequencies, damping ratios and mode shapes of the first stage of the Vega lunch vehicle will be investigated in order to asses the overall efficiency of such approaches. Copyright © 2011 by G. Coppotelli, C. Grappasonni, C. Di Trapani
Output-Only Analyses in Environmental Testing
No full textEnvironmental tests are widely used to qualify structures for space missions, because the benchmark test facilities allow the replication of the loading conditions acting on a system during the different phases of the mission. In this paper, an Output-Only-based tech-nique is proposed to estimate the full modal parameters, in the frame of the environmental test-ing, to increase the accuracy of the dynamic identification and to reduce the overall time and cost associated to the qualification process. The Output-Only Modal Analysis approach, de-noted as Hilbert Transform Method by the authors, will be applied for the estimate of the "bi-ased" Frequency Response Functions, FRFs, whereas the evaluation of the modal masses asso-ciated to each mode will be carried out by the application of various mass perturbation methods available in literature. The robustness of these approaches will be assessed through environ-mental tests carried out on spacecraft structures, such as a robotic arm intended for space appli-cations and a tank prototype of the Vega launcher. The accuracy of the proposed method will be finally evaluated by comparing the FRF estimates, obtained with the Output-Only approach, with the ones gained using the standard input/output technique. Copyright © (2011) by International Operational Modal Analysis Conference (IOMAC) All rights reserved
Operational Modal Analysis of a Helicopter UAV from Flight Tests
No full textThe Operational Modal Analysis (OMA) could be used for the identification of the dynamics of aerospace vehicles, in terms of natural frequencies, damping ratios and mode shapes, during flight tests, using only the output responses due to the aerodynamic envinronment. The loading acting on the flying helicopter is composed by the contributions of both the white noise excitation and the aerodynamic harmonics acting at discrete operational fre-quencies equal to the multiple of the fundamental angular velocity of the rotor. As a result, the system could not be considered excited by a pure white noise input and then the OMA methodologies could not be theoretically applied to the output responses to estimate the dynamical behavior of the helicopter. In this paper an approach is developed to cope with this problem. First, a method based on the statistical index, called Entropy, is introduced to identify such op-erational frequencies by means of a statistical characterization of the responses of the structure due to deterministic input superimposed to stochastic noise. Then, the effects of the removal of the previous identified harmonic contributions from the Frequency Response Functions (FRF) gained, in turn, by applying the procedure known in literature as Hilbert Transform Method, HTM, will be evaluated. In order to assess the overall accuracy in the modal parameter esti-mates, an experimental investigation, carried out on a helicopter UAV flying at different condi-tions, i.e. in- And out-of-ground effect hovering and forward flight at several advance ratios, will be presented. Copyright © (2011) by International Operational Modal Analysis Conference (IOMAC) All rights reserved
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
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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