1,721,103 research outputs found
Wind tunnel tests on railway vehicles in the presence of windbreaks: Influence of flow and geometric parameters on aerodynamic coefficients
Get PDFCrosswind stability is one of the most studied topics in the field of train aerodynamics. The interaction between a train and strong crosswinds can lead to the train overturning. One way to reduce the train overturning risk is to equip the railway line with windbreak barriers. In this work, the results obtained during wind tunnel tests on an ETR1000 high-speed train in the presence of different types of windbreaks are shown. The goal is to underline the effects of different flow parameters and geometric parameters of the infrastructure's models on the train's aerodynamic coefficients. Comparing the different test results made it possible to provide indications on which parameters are important to avoid experimental errors and reproduce as much as possible the real full-scale phenomena. Particular attention shall be paid to the dimensions of the splitter plate because a limited upwind width can lead to underestimation of aerodynamic coefficients by more than 30%. The length of the barriers in front of the train is fundamental and too short length can lead to coefficients overestimation of about 25%. Finally, coefficients measured with only the upwind windbreak row are lower (up to 50%) than those measured with a two rows configuration
High-speed freight trains for intermodal transportation: Wind tunnel study on the aerodynamic coefficients of container wagons
Get PDFThe paper investigates the response to crosswind of a high-speed freight train for intermodal transportation, through wind tunnel tests. A 1:20 model of a freight train composed by an engine and two flat-car vehicles was instrumented with force balances to measure the aerodynamic coefficients of the flat-car plus container assembly and of the container alone. Aerodynamic coefficients strongly affects the train stability and the anchorage limits of the container itself. During the wind tunnel tests, eight different loading configurations were considered and aerodynamic coefficients were determined for yaw angles (i.e. angle between train and wind) ranging from 0° to 90°. Experimental results show the benefits in terms of drag reduction due to the presence of a laden vehicle upstream. As far as the rollover risk is concerned, the less critical condition is found for a vehicle preceded by a fully laden wagon and followed by an empty one. More in particular, at low yaw angles, the worst condition for a vehicle occurs when the wagon ahead is empty while, for yaw angles between 45° and 55° which are the most critical for ‘low speed’ trains, the differences with respect to the other configurations reduce significantly
A centimetre-scale bi-directional wind turbine for energy harvesting applications: Design and experimental tests
No full textIn this work, new cm-scale wind turbines for powering sensor nodes devoted to monitoring/diagnostic of railway vehicles are designed, built and tested in a wind tunnel. Two rotors, having four airfoil blades with a diameter of 3 and 4 cm, are designed following the blade element momentum-based approach. The two rotors, tested in a wind tunnel, reach a power coefficient (without considering the losses in the conditioning circuit) ranging between 20% and 30%, in line with the maximum values of the Schmitz theory; the correspondence between the numerical estimates and the experimental data is discrete. The 4 cm diameter rotor, once connected to a conditioning circuit, reaches a maximum net efficiency of about 15%, equal to the maximum value found in the literature, but with a 13,5 cm diameter rotor. Considering the practical application on trains and the fact that the rotor has to work for two opposite velocity directions (it must be bi-directional), a 4 cm diameter symmetrical rotor with a constant blade pitch and flat plate blade section is also built. With the symmetric rotor, we can observe that the generated power is about 50% lower than that produced by the same rotor with airfoil blades. Finally, the turbine is set inside a duct to protect it and increase performance. The tests performed on this ducted turbine (4 cm diameter, symmetric) allow us to understand that the duct significantly increases the performance of the rotor in downwind conditions, from 1% to 6%, while it is almost irrelevant in upwind conditions. Moreover, the diffuser increases the efficiency by about 20%, while the contraction cone does not significantly modify the performance of the turbine
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
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