1,720,956 research outputs found
MACHINE-LEARNING METHODS FOR DATA ANALYSIS AND OPTIMIZATION OF LPT CASCADES
No full textThe present thesis is aimed at presenting some advancements and opportunities provided
by modern machine-learning (ML) tools for data analysis and optimization in the field of
aeroengine Low-Pressure-Turbine (LPT). Specifically, in this work the ML tools led to
the definition of: (O1) a proposal for a new profile loss correlation for LPT cascade, (O2)
a blade geometry model to be used alongside the loss correlation for the identification of
the optimal LPT blade shapes, and (O3) a new sampling strategy for the optimization of
future test campaigns based on either experiments or numerical simulations.
A vast database concerning LPT blade aerodynamic performance has been experimentally
acquired during the work and has been used as foundation for the application of the ML
tools. The database includes the results of several low-speed tests carried out in two wind
tunnels installed in the Aerodynamic and Turbomachinery Laboratory of the University
of Genova for different families of LPT cascades and for many different operating conditions.
The tests also account for the unsteady aerodynamic interaction between the stator
and the rotor, that has been simulated during the experiments by means of a moving bars
system.
For accomplishing the objectives of the work, regression tasks have been addressed. Pros
and cons of linear, regularized and non-linear regression models have been deeply analyzed.
The advantages provided by Gaussian Processes are particularly highlighted in this
thesis. Bayesian and Cross-validation criteria have been used for model selection. Especially,
a new robust strategy for the identification of the right compromise between model
accuracy and generalizability has been defined and presented in this work. It led to the
definition of the new profile loss correlation (O1), which overcomes existing ones because
it accounts for the unsteady effects, and because it is dynamic, i.e., easily updatable with
new data every time it is deemed necessary. The new correlation led to the identification
of a new optimal LPT cascade, the results of which allows the validation of the model and
provides further enlargements.
ML tools for dimensionality-reduction have also been used to analyze high dimensional
data. The Proper Orthogonal Decomposition (POD) has been moved from the classical
fluid dynamic framework toward unconventional applications for modelling loss coefficient
distributions and interpreting blade geometries. A POD-based geometry model (O2)
able to generate LPT blade shapes from a set of few geometrical parameters has been defined.
It can be used alongside the loss correlation to quickly provide optimal interpolated
blade shapes in the LPT design regions that are expected to minimize losses. Moreover,
a POD-based sampling strategy (O3) has been proposed for the identification of the tests
that are strictly needed for modelling the cascade performance. Such procedure may be
useful for optimizing new campaigns of cascade tests, and more in general to observe the
response of a new system with respect to the parameter variation with a coarse grid sampling
the design space. The results here obtained constitute a direct support for LPT aero design, while the used ML procedures can be extended to other engineering applications
Flow Coefficient and Reduced Frequency Effects on Low Pressure Turbine Unsteady Losses
No full textarticle image velocimetry measurements have been carried out in a low-pressure turbine cascade operating under unsteady inflow to deeply investigate reduced frequency and flow coefficient effects on flow dynamics, and, consequently, on loss generation in the boundary layer and in the core flow region. Two independent measuring setups have been used for the purpose. The first one captured a large view of the entire blade passage, thus allowing the observation of the incoming wakes and related large-scale vortices developing in the core flow region. The second setup was instead focused on the rear part of the blade suction side to analyze the boundary layer development and to observe the mechanisms dominating the wake–boundary- layer interaction. Tests were performed for four flow cases, varying the reduced frequency and the flow coefficient independently. Proper orthogonal decomposition has been applied to quantify the turbulent kinetic energy production in the core flow, due to wake dilatation and distortion, and in the boundary-layer region. Upstream wake migration and boundary-layer-related losses are consequently quantified from particle image velocimetry data and compared with total pressure measurements for the different combinations of the inflow parameters, providing a clear view of the different loss sources affecting the unsteady operation of low-pressure turbine cascades
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
