1,720,957 research outputs found
Model validation and uncertainty qualification for the preliminary aero-engine design process
No full textThis thesis investigates the design decisions taken during the preliminary aero-engine design process where the amount of knowledge is limited, although deciding on fuel efficiency, noise, emissions, weight and overall performance occurs within this stage. In order to not commit all resources during this phase, those decisions are made using low fidelity models. Unfortunately, the results from low fidelity models lack accuracy, so there is a natural need to take this into account. Improving those low fidelity methods via uncertainty quantification methods is the main theme of this thesis. In order to create accurate models for the preliminary design stage of the aero engine, a probabilistic framework was created and implemented. This framework is based upon suggestions from the literature and was constructed from two main components: expert systems as well as Bayesian inference. The way in which this was developed will be shown in detail later. This framework was applied to three aero-engine related case studies which reflect the need to have more knowledge available during the preliminary stage. The results obtained from the framework have the form of predictions which offer information which was not available otherwise. For the fan-blade off case study, the posterior predictive distributions show what the characteristics of the most likely events are, and this information can be used to make the detailed design stage less expensive by doing fewer finite element analysis simulations. For the grain growth case study, the results show what probability distributions the manufacturing inputs should have in order to keep the size of the grain within certain limits in order to maximize the life cycles. Finally, the results obtained with regards to fatigue failure due to non-metallic particle inclusions show how component life as well as failure cause can be obtained. This type of knowledge was not previously available in the literature, and making use of it can avoid removing components from their service too early
Uncertainty quantification via elicitation of expert judgements
No full textThe purpose of this paper is to depict one method of quantifying uncertainty about different parameters, which is based on eliciting judgements either from a single expert or from a group of experts. The quantities obtained as a result of the elicitation are therefore used in order to fit probability density functions (PDFs) by using an in-house MATLAB model which uses appropriate fitting techniques similar to the ones suggested in the existing literature. Consequently, an initial framework has been implemented which would first of all allow the comparison of elicited data with the experimental results. The underlying theory behind the elicitation process is being presented and subsequently an aero-engine Fan Blade Off (FBO) case study is presented. The framework is used to illustrate the way in which expert judgements are implemented as inputs into the MATLAB model which is used to predict different parameters of interest associated to FBO events such as probabilities of having a particular speed during an event as well as what are the characteristics of the most likely events to occur. Those are taken into consideration in order to allow the designer to perform relevant and more detailed analysis on the fan subsystem during the preliminary design process
Quantifying uncertainties during the early design stage of a gas turbine disc by utilizing a bayesian framework
No full textQuantifying uncertainties regarding the grain size of the turbine disk has been identified as a crucial aspect for the preliminary design stage. The reason for that is because the grain size is correlated to the life of the component which should preferably be maximized or at least quantified to the best of the designer’s abilities. In the grand scheme of things, this ultimately translates into a potential competitive advantage for the aero engine company. The prime focus of this paper is the investigation of material properties which was done by combining simulation and experimental data within a Bayesian framework in order to enhance the decision making process during the preliminary design stage. The aim of the case study presented here was to show how the physical processes can be modelled using a Bayesian network which updates prior probability distributions with real data in order to obtain more accurate predictors of reality. The first part of the paper explains the theory behind the framework, while the latter half shows some results as well as some conclusions which can be drawn.</p
Model Validation and Uncertainty Quantification of the Preliminary Aero-Engine Design Process
No full textGoing 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
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