1,720,975 research outputs found
Predicting the noise of an open rotor in a wind tunnel
No full textA study of the impact of reverberation on cruise regime acoustic testing of contra-rotating open rotors in a wind tunnel is presented. Models for the rotor tone noise generated in closed cross-section wind tunnels are derived and used in the analysis. The models account for rectangular and circular cross-sections, rigid or impedance boundaries and, for the rectangular wind tunnel case, the rotor axis may be arbitrarily located within the tunnel (but aligned with the flow direction). These models are used to generate simple simulations of model-scale open rotor testing in two real wind tunnels suited to high-speed rotor testing – the Transonic Wind Tunnel in Bedford, UK and the S1MA wind tunnel in Modane, France. In the analysis, the effect of various modelling parameters on the reverberant noise field is investigated. It is shown that open rotor interaction tone noise may be particularly susceptible to the impact of reverberation and that for many tones the reverberant field may persist and contribute to a contaminated noise field, even for wind tunnels with acoustic treatments on the walls of the working section.</p
On the optimum separation distance for minimum noise of contra-rotating propellers
No full textOverlapping propeller systems are currently used on some urban flight vehicles and will become increasingly common in future electric propulsion, since they provide one of the most compact platform volumes per thrust. This paper presents the results of a detailed experimental investigation of co-axial contra-rotating propeller configuration at hover condition. A detailed parametric study is performed to investigate the sensitivity of radiated noise to axial separation distance. An optimum separation distance z to propeller diameter D of 0.25 has been identified, whereby minimum radiated noise is obtained. The reason for this optimum has been explored and the balance between various interaction noise sources in co-axial configuration is discussed in the paper. It is also shown that the minimum radiated noise was roughly found where the aerodynamic efficiency is maximum
Analytical investigation of propeller-wing interaction noise
No full textThis paper investigates the noise generated by propeller-wing configuration at take-off condition with the propeller mounted upstream. This study makes use of various axisymmetric noise models developed for contra-rotating propellers to estimate the noise generated by propeller-wing configuration and later integrate them to estimate total noise. First, using well-published theory, rotor-alone (loading, thickness, and self-noise) and interaction noise sources (viscous-wake, potential field, tip-vortex) including tonal and broadband components are estimated. Later, a systematic parametric study is carried out by changing the blade number and tip Mach, while maintaining the propeller thrust and blade solidity. The noise generated is represented by Overall Acoustic Sound Power Level (OSWLs), which is an integrated value over the emission angles and frequency range, in a matrix form for the range of blade number and tip Mach. This matrix shows the regions dominated by rotor-alone and interaction noise and found that the noise characteristics of a rotor in uninstalled conditions (rotor-alone) are significantly altered due to the presence of a wing (installed condition). Further, it is found that the balance between these regions shifts with the variation in separation distance between the propeller and the wing. These results are further discussed with the individual interaction noise source mechanism and their dominance at various blade numbers, tip Mach, and separation distances. In addition, the non-axisymmetric viscous-wake interaction noise is investigated for even and odd numbers of blades and found that viscous-wake interaction noise has considerable directivity in the azimuthal direction. The results presented in the study are preliminary findings of propeller-wing noise, however, it gives give a quantitative picture of the behaviour of various noise sources and their balance with respect to geometric and operating parameters. This study will help to understand the dominant noise sources involved in propeller-wing configuration and will provide a quick guide for designing a low-noise configuration
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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