1,720,969 research outputs found
Application of sweep to transonic compressor rotor blades for low-order statistical moment averaging in robust design
No full textRobust design optimization involves finding the low-order statistical moments, i.e. the maximization of some mean quantity of interest and minimization of its variance. The question arises as to when a mean or variance value can be considered to be converged to an acceptable level of certainty. A designer naturally seeks to keep the number of function evaluations as low as possible when converging statistics. There is no general answer to the question of how many CFD simulations need to be carried out in order to obtain reliable estimators and which sampling methods perform better. Furthermore, multi-fidelity optimization techniques such as Co-Kriging can be used to combine different convergence levels and the question remains as to how many functions evaluations should be carried out. Practical guidelines applicable for the robust design optimization of turbomachinery blades are provided here. The applied methodology involves the freely available NASA Rotor 37 geometry and 3D steady-state RANS-based CFD with the Spalart-Allmaras turbulence model. The numerical CFD results are validated against actual experimental results. A uniformly distributed sweep uncertainty applied at the tip of the blade is propagated using Monte Carlo and Quasi-Monte Carlo-based sampling (low-discrepancy Halton and randomized Sobol sequence) for comparisons. Statistical post-processing of the results is based on 500 CFD runs for each sampling strategy. As an indicator of the error bounds, standard deviation and confidence intervals for the converging sample means of all quantities of interest are calculated. The required number of iterations is estimated
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
(Re-) Meshing using interpolative mapping and control point optimization
No full textThis work proposes a simple and fast approach for re-meshing the surfaces of smooth-featured geometries prior to CFD analysis. The aim is to improve mesh quality and thus the convergence and accuracy of the CFD analysis. The method is based on constructing an interpolant based on the geometry shape and then mapping a regular rectangular grid to the shape of the original geometry using that interpolant. Depending on the selected interpolation algorithm the process takes from less than a second to several minutes. The main interpolant discussed in this article is a Radial Basis Function with cubic spline basis, however other algorithms are also compared. The mesh can be optimized further using active (flexible) control points and optimization algorithms. A range of objective functions are discussed and demonstrated. The difference between re-interpolated and original meshes produces a metric function which is indicative of the mesh quality. It is shown that the method works for flat 2D surfaces, 3D surfaces and volumes
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
An integrated framework for Bayesian uncertainty quantification and probabilistic multi-criteria decision making in aero-engine preliminary design
No full textThe following paper presents a novel framework that enables making early design decisions based on probabilistic information obtained from fast, deterministic, low-fidelity tools, calibrated against high-fidelity data that is supported by experts’ knowledge. The proposed framework integrates a Probabilistic Multi-Criteria Decision Making technique with Bayesian Uncertainty Quantification concepts supported by the Kennedy and O’Hagan Framework. It allows continuous improvement of low-fidelity design tools as high-fidelity data is gathered and therefore facilitates investigation into the impacts the accumulation of high-fidelity data has on preliminary design process risk. The paper discusses theoretical concepts behind the framework and demonstrates its relevance by application in an illustrative combustor preliminary design case study
Robust turbine blade optimization in the face of real geometric variations
No full textBecause of manufacturing variations, no real turbine blade exactly conforms to its nominal geometry. Even minimal deviations are known to affect aerodynamic performance, blade temperatures, and blade lifespan negatively. Rather than conventional deterministic design with its costly adherence to strict control of tolerance limits, robust design optimization aims to incorporate inevitable variations into the design process itself, so that both performance mean and scatter can be optimized simultaneously. Such a workflow is presented and applied in this paper to aerodynamically optimize an industrial turbine rotor blade against realistic manufacturing variations. A set of digitized three-dimensional laser scans from two turbofan engines forms the core of this study. On the basis of these deviations, the approach uses high-fidelity geometric models, nonintrusive uncertainty quantification, and efficient robust optimization with constraints to effectively locate Pareto-optimal designs. One selected robust blade is validated and shown to be desensitized to the observed manufacturing variability. The underlying measurement data are crucial to obtain realistic results and, as a consequence, are vital to design real robust turbine blades
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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