1,720,957 research outputs found
Pressurizing Gas Effects on Pressure Oscillations during the Ignition Transient of SRM's
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On the NDP onset in pre-ignition transient of high performance SRMs: VEGA Z9A experience
No full textThis paper discusses the early phase of the ignition transient of the VEGA Launcher's third stage solid rocket motor, Zefiro 9A. During the first two firing tests of the Z9A SRM (QM2 and VT1) a peculiar unexpected negative force peak and a significant pressure unbalance in the motor chamber were measured during the very first phase of the ignition transient. In order to fix the unexpected negative force, out of the system specifications, a modification of the igniter re-design was decided for the Z9A SRM and a third static firing test was successfully carried out (VT2), with a reduction of the negative differential pressure of at least around a factor 3, followed by a reduction of the negative thrust by around the same factor. This paper wants to analyze the scenario outlined by the VT2 static firing test by means of three dimensional unsteady multi-component numerical simulations of the SRM pre-ignition transient. © 2011 IEEE
Q1D Modeling of SRM Aeroacoustics
No full textLow amplitude but sustained pressure and thrust oscillations can characterize the quasi-steady condition of solid rocket motor; notwithstanding they are not threatening for motor life, coupling to the structural modes, they can damage the payload. These oscillations are due to fluidynamics instabilities and acoustic coupling. In this paper the AGAR (Aerodynamically Generated Acoustic Resonance) code is presented, a simplified method to predict both oscillation frequencies and amplitude with reduced computational costs and times, describing the excitation of acoustic modes accounting for the acoustic feedback on the vortex shedding phenomenon. A brief description of the method and of the principal obtained numerical results is presented
Static firing ballistic reconstruction modelling and performance extrapolation to flight in srms
No full textAn independent assessment of the steady-state and tail-off ballistic performance of the first static firing test of Zefiro 40 DM solid rocket motor has been performed. The analysis is carried out with a post-firing 0D quasi-steady performance reconstruction model, developed for the purpose and already used for the analysis of SRM SFTs. The study has been focused on two different aspects: i) the SFT ballistic performance analysis with the reconstruction of the non-ideal parameters and the performance extrapolation to flight configuration; ii) the motor performance extrapolation to flight unit based on the reconstructed non-ideal parameters and exploiting the SFT to flight expertise of Zefiro 23 and Zefiro 9 SRMs. The final goal is to increase the understanding of VEGA’s solid rocket motors behavior in terms of non-ideal parameters and to consolidate the methodology used for the performance reconstruction and extrapolation to flight uni
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
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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