1,720,960 research outputs found
Big data enabling quieter and cleaner air transport
Get PDFAbstract: prima parte
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The steady growth of air traffic, only temporarily halted by COVID-19, is causing several problems in the management of flight movements around civil airports, leading to congestion, delays, and ultimately increased noise and pollutant emissions in airport areas. These emissions can be estimated with several prediction models, but the lack of input data on flight movements often limits their effectiveness. In recent years, however, the introduction of ADS-B transponders and the development of the Internet have led to the birth of flight tracking websites, which report and offer to the public large amounts of information on aircraft movements and airport weather conditions. At the same time, many websites provide complementary information on aircraft models and engines, airport layouts, and topography of airport areas.
This thesis presents an innovative modelling tool that enables calculation of noise, chemical emissions, and pollutant dispersion from civil air traffic in airport areas on the basis of input data collected from the Internet. The reconstruction of aircraft flight performance and emissions relies on pre-existing prediction models, which require special implementation to deal with the Internet-based input data.
The first operation performed by the present modelling tool is the reconstruction of air traffic in airport areas. The flight tracking and weather data are collected from flight tracker FlightAware and combined in a pre-processing stage with information on aircraft models/engines and airport runways to define daily departures and arrivals, collectively named flight events. Future traffic scenarios are also built from historical flight events accounting for fleet renewal and air traffic increase according to EUROCONTROL forecasts with two custom-made algorithms.
The flight events are then processed to reconstruct the aircraft motion over time during each event. This is done by determining the segmented flight path, which is built by merging the ground track with the flight profile. The former represents the aircraft motion on the ground and is calculated with a specially developed algorithm, while the latter consists in the variation of height, speed, and thrust along the ground track and is modelled relying on the ECAC flight procedures.
The processing goes on to calculate noise and chemical emissions. First, a specially implemented version of the ECAC Doc 29 model is used to compute single-event noise levels in the airport area using a 2-D grid of observers, and then engine fuel flow and emissions of HC, CO, NOx, PM2.5, SO2, CO2, H2O are calculated on the basis of the FAA’s AEDT methodology. An empirical correlation from the literature is also included to estimate NO2 emissions. In the final stage, all results concerning emissions are obtained. Cumulative noise metrics and indices are computed from single-event noise levels, while emission inventories are built from the previously calculated chemical emissions. The released amounts of pollutants NO2, PM2.5 and SO2 are then extracted and allocated spatially in the airport area. This allocation leads to a number of pollutant emission sources that are fed, together with the weather data, into AUSTAL2000, which provides the pollutant concentration levels around the airport.Abstract: seconda parte
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Two data collection campaigns were run in June 2018 and July 2019, and daily flight tracking data were retrieved for several European airports of different sizes and traffic intensity. Comparisons with EUROCONTROL data show a good reconstruction of air traffic for 2018 and an excellent one for 2019, highlighting also the reasons why discrepancies exist. Ground track maps, noise contour maps, and noise levels at monitoring stations around Heathrow, Gatwick, Schiphol, and Vienna International airports are compared with official results, showing an overall very good agreement but indicating that departure flight profiles need improving. Future traffic scenarios for 2025 were built using the 2018 traffic data for Heathrow, Frankfurt, and Vienna airports, and the changes in noise contour maps and areas suggest that the algorithms for fleet renewal and additional flight events are highly effective.
The calculation of emissions and pollutant dispersion was made using only the 2019 traffic data. The comparison of modelled and official emission inventories for Heathrow indicates that aircraft emissions are modelled well, although limited underestimations are observed. On the contrary, the poor comparison between measured and modelled pollutant concentration levels around Heathrow, Gatwick and Madrid-Barajas airports shows very clearly the need for considering non-aircraft emissions and for a better spatial allocation of pollutants released during taxi operations.
Thanks to an innovative approach that consists in exploiting Internet-based data sources, the present modelling tool can be applied to any airport worldwide for any time period, enabling assessment of the environmental impact of past, present and future air traffic scenarios. As soon as a few upgrades are implemented, this tool will be able to assist policy-makers in developing guidelines and regulations aimed at mitigating the detrimental effects of air traffic around civil airports
A consistent model of the initiation, early expansion, and possible extinction of a spark-ignited flame kernel
No full textModelling the establishment and growth of spark-ignited (SI) flame kernels has always been a topic of great interest, especially due to their key role in affecting the performance of SI engines. A major issue is that the unsteady conditions and the small kernel size hinder the application of the typical (both linear and non-linear) flame stretch correlations, valid only long after the ignition stage. Overcoming such limitations, this work presents a novel, mathematically consistent, and compact model that enables prediction of flame kernel initiation and early expansion, including its possible extinction. Firstly, spark-driven initiation models from literature are discussed, and an effective flame kernel initiation method is proposed. Then, the expansion model is defined complementing the mass, energy, and species conservation equations for the spherical kernel with the reactant and temperature profiles outside of it using the theory of transient thermodiffusive flames. After accounting for the convective flow caused by the combustion-induced density reduction and the variable thermodynamic properties of the reacting fuel/air mixture, the result is a two-equation model that predicts the kernel expansion even up to its possible extinction due to flame stretch. After calibration of the expansion model, successful validation is achieved against literature data on lean propane/air flames, and the influence of the model parameters is examined in detail. The proposed expansion model is formulated also aiming for inclusion into the simulation of combustion in SI engines, enabling more accurate predictions at part loads, as well as more effective estimation of the cycle-to-cycle variation thanks to the good model sensitivity to the parameters most affecting the ignition
Estimating the minimum ignition energy of spark-ignited fuel/air mixtures: preliminary steps towards a novel modelling approach
Get PDFIn spark-ignition (SI) engines, the achievement of a fast combustion with low cycle-to-cycle variation is highly dependent on the successful initiation of a flame kernel from the spark plug. Its growth can be sped up by increasing the electrical energy supply, but at the cost of higher plug wear, whereas too little energy may result in an ignition failure. Therefore, knowledge of the minimum ignition energy (MIE) of a fuel/air mixture is of key importance to guarantee a proper combustion process at minimal cost. To model the MIE several approaches have been proposed in literature, primarily derived from the experiments conducted by Lewis and Von Elbe and their resulting theory of quenching distances. However, these approaches appear in conflict with more recent experimental outcomes, and the impact of the ignition device is neglected. This work proposes a novel approach for modelling the MIE, which is based on a flame kernel expansion model recently proposed in another paper. In this approach, the proposed model, which has general validity, is specialized to the particular case of the estimation of the MIE, supplied via an electrical breakdown. A model advancement is also included that consists in the quantification, albeit at a preliminary level, of the impact of different gap distances and spark plug quenching effects on the flame kernel development. The results are validated against literature models and experimental data for two fuels, propane and hydrogen, and multiple equivalence ratios. In contrast with the noticeable MIE overestimation of literature models, for propane the proposed approach leads to better results compared to the experiments. Instead, for hydrogen a tendency towards a MIE underestimation is observed, especially for lean mixtures. The model is also tested for SI-engine-relevant conditions, showing satisfactory overall trends. The key source of error seems related to the very complex kernel-electrode interaction, the modelling of which will be improved in future developments
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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