1,720,957 research outputs found
Cost optimization tools for advanced gas turbine technologies
No full textThis thesis presents two studies that illustrate how cost modelling can be integrated into the various design process stages, ranging from strategic gas turbine and airframe system design to preliminary and detailed component design and production planning. The first study investigates which cruise speed the next generation of short-haul aircraft with 150 seats should fly at and whether a conventional two- or three-shaft turbofan, a geared turbofan, a turboprop or an open rotor should be employed in order to make the aircraft's direct operating cost robust to uncertain fuel and carbon (CO2) prices in the Year 2030, taking the aircraft productivity, the passenger value of time and the modal shift into account. To answer this question, an optimization loop was set up in MATLAB consisting of nine modules covering gas turbine and airframe design and performance, light and aircraft fleet simulation, operating cost and optimization. If the passenger value of time is included, the most robust aircraft design is powered by geared turbofan engines and cruises at Mach 0.80. If the value of time is ignored, however, then a turboprop aircraft flying at Mach 0.70 is the optimum solution. This demonstrates that the most fuel-efficient option, the open rotor, is not automatically the most cost-efficient solution because of the relatively high engine and airframe costs. The second study shows how a factory cost model can be combined with a parametric component production time model, to not only calculate costs at the manufacturing operation level for production planning, but also the total unit costs of future integrally bladed disc (blisk) designs for component trade-off studies. As future process times can only be estimated and the correlation between operation times and blisk design parameters, including the number of blades, the disc diameter and other design variables, is never perfect, all operation times have uncertainty distributions. These are cascaded through the model to generate a probability distribution of the unit cost
Strategic jet engine System design in light of uncertain fuel and carbon prices
No full textSince the Wright brothers took to the skies over 100 years ago, aviation has been powered by fossil fuels. This dependency will not be markedly reduced within the next two decades despite higher and more erratic fuel prices that result from increasingly restricted access to crude oil. Climate change will also force regulators to increase the price of CO2 emissions so that there is an even greater incentive to operate fuel efficient aircraft. This project therefore aims to investigate how the profit generated by a short-range jet engine can be made robust to uncertain fuel and carbon prices in 2030 by applying the Surplus Value Methodology in conjunction with Robust Design techniques
Robust gas turbine and airframe system design in light of uncertain fuel and CO2 prices
Full text linkThis paper presents a study that numerically investigated which cruise speed the next generation of short-haul aircraft with 150 seats should fly at and whether a conventional two- or three-shaft turbofan, a geared turbofan, a turboprop, or an open rotor should be employed in order to make the aircraft's direct operating cost robust to uncertain fuel and carbon (CO2) prices in the Year 2030, taking the aircraft productivity, the passenger value of time, and the modal shift into account. To answer this question, an optimization loop was set up in MATLAB consisting of nine modules covering gas turbine and airframe design and performance, flight and aircraft fleet simulation, operating cost, and optimization. If the passenger value of time is included, the most robust aircraft design is powered by geared turbofan engines and cruises at Mach 0.80. If the value of time is ignored, however, then a turboprop aircraft flying at Mach 0.70 is the optimum solution. This demonstrates that the most fuel-efficient option, the open rotor, is not automatically the most cost-efficient solution because of the relatively high engine and airframe costs
Strategic jet engine system design in light of uncertain fuel and carbon prices
No full textThis paper presents a project that is investigating which cruise speed the next generation of short-haul aircraft with 150 seats should fly at and which combination of advanced engine technologies should be employed in order to make the profit generated by the aircraft robust to uncertain fuel and carbon prices in Europe in 2030. To answer this question, an optimization loop is being set up in MATLAB consisting of five modules, including an aircraft design, a travel demand, a modal shift, a flight profile, and an engine design element. The first three modules were tested in a preliminary study that analyzed the effect of high and low fuel and carbon prices on the optimum aircraft design and its ideal cruise speed. The results indicate that if oil and CO2 prices were to rise significantly, a slower turboprop aircraft would be more profitable in terms of Surplus Value in comparison to a conventional turbofan design. If prices were to reduce, however, a faster turbofan aircraft would offer a superior business case. The study also showed that making realistic Surplus Value predictions is more difficult than forecasting costs
An activity-based-parametric hybrid cost model to estimate the unit cost of a novel gas turbine component
Full text linkThe first tool presented in this paper is a generic factory cost model that can estimate various costs at multiple levels of any manufacturing plant. The model is activity based which means that the cost of each manufacturing operation is calculated and then summed up so that the true £-per-hour factory cost rate as well as the exact unit cost (i.e. manufacturing cost) of an unlimited number of different components can be estimated.The second tool is a scalable cost model that predicts the unit cost of future integrally bladed disc (blisk) designs that are found in gas turbine compressors. The tool multiplies the machine cost rates, calculated by the factory cost model, by the operation times derived from blisk scaling rules. As the operation times often depend on the number of blades, the disc diameter and other design variables, many scaling rules are based on the correlation between operation times and certain design parameters. Conversely, the remaining process times are constant because they are independent of the blisk geometry. As future process times can only be estimated and the correlation between operation times and design parameters is never perfect, all operation times have uncertainty distributions. These are cascaded through the model to generate a probability distribution of the unit cost.Through the interactive exchange of detailed cost information at the manufacturing operation level as well as extrapolated operation times, the two cost models facilitate design and manufacturing engineering to concurrently optimise blisk designs and manufacturing processes in terms of cost
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
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
- …
