1,721,026 research outputs found
Assessment of the thin-airfoil method for predicting steady pressure distribution on partially-porous airfoils
No full textBoundary layer characterization and acoustic measurements of flow-aligned trailing edge serrations
No full textTrailing edge serrations designed to reduce airfoil self-noise are retrofitted on a NACA 0018 airfoil. An investigation of the boundary layer flow statistical properties is performed using time-resolved stereoscopic PIV. Three streamwise locations over the edge of the serrations are compared. An analysis of the results indicates that, while there is no upstream effect, the flow experiences significant changes as it convects over the serrations and toward its edges. Among the most important, a reduced shear stress and modifications of the turbulence spectra suggest beneficial changes in the unsteady surface pressure that would result in a reduction of trailing edge noise. Microphone array measurements are additionally performed to confirm that noise reduction is indeed observed by the application of the chosen serration design over the unmodified airfoil.AerodynamicsAircraft Noise and Climate EffectsWind Energ
Aircraft Noise Prediction: A comparison between current established methods
No full textNoise prediction models are critical to assess the noise production of aircraft. They are of growing importance due to the increase in air transport and population. This research focusses on the comparison of the noise predictions of empirical and semi-empirical models. The noise predictions of NIROS, an empirical noise prediction model used by Deutsche Flugsicherung (the German air traffic control), are compared with the noise predictions of the DLR model PANAM. Both models are assessed on their use, applicability and limitations using a simulation case. Three major difference were found during the initial research i.e. the use of Noise-Power-Distance tables in empirical noise modelling and noise source modelling in semi-empirical noise models, the differences in noise propagation methods applied for ground reflection and atmospheric absorption and the differences in the construction of the flight path. A simulation case was constructed to further examine the differences in the noise predictions of both models. In PANAM and NIROS an A319 was used to simulate the noise for observers located on the ground. The results of the simulations showed higher noise levels in PANAM than in NIROS. Furthermore the difference in flight path and the applied ground reflection method had the biggest influence on the simulation results. Better understanding of the differences between the models can be used to make improvements to the fully empirical method.Aerospace EngineeringControl & OperationsAircraft Noise and Climate Effects (ANCE
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
Assessing noise level variability in fly-over data
No full textAs the air travel industry steadily grows, so does the noise pollution that comes with it. This brings with it a myriad of socio-economic consequences, especially in the vicinity of airports. In order to combat this aircraft noise at its origin, it is important to know where it originates from and determine the prevalent sound sources on an aircraft and their contribution to the noise. The goal of this research is to determine the different aircraft noise sources in fly-over data collected by a microphone array during landing. In addition to locating the prevalent noise sources, also the variability is assessed. Subsequently it is investigated to what extent the engine settings and aircraft velocity affect the sound levels of the noise produced by these sources. The data used to accomplish this goal was collected from 115 fly-overs at Schiphol Airport on two separate measurement days, using an acoustic array with 32 microphones that was developed at the faculty of Aerospace Engineering. Of these measurements, 43 Boeing 737 “Next Generation” fly-over measurements were selected for analysis. Using beamforming, the locations of different sound sources and their corresponding sound pressure levels were determined. After defining different sound signals from the fly-over data, using conventional delay-and-sum beamforming on these signals, various noise sources at the engines and a noise source at the wings were located. The correlation of these noise sources sound pressure level with the engine setting and velocity was also investigated. This helped to further determine the origin of the noise.Aerospace EngineeringControl & OperationsAircraft Noise and Climate Effects (ANCE
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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