1,721,105 research outputs found
An alternative definition of order dependent dissipation scales
No full textWhile Kolmogorov's similarity hypothesis suggests that velocity structure functions scale with the mean dissipation \left and the viscosity , we find that the even order scales with \left. This implies that there are other cut-off lengths than the Kolmogorov length . These cut-off lengths are smaller than and decrease with increasing order and Reynolds-number. They are compared to a previous definition of order dependent dissipative scales by Schumacher~et.~al\cite{schumacher2007asymptotic}
Unsupervised Data Analysis of Direct Numerical Simulation of a Turbulent Flame via Local Principal Component Analysis and Procustes Analysis
Full text linkDirect Numerical Simulations (DNS) of reacting flows provide high-fidelity data for combustion model reduction and validation, although their interpretation is not always straightforward because of the massive amount of information and the data high-dimensionality. In this work, a completely unsupervised algorithm for data analysis is investigated on a data-set obtained from a temporally-evolving DNS simulation of a reacting n-heptane jet in air. The proposed algorithm combines the Local Principal Component Analysis (LPCA) clustering algorithm with a variables selection algorithm via dimensionality reduction and Procustes Analysis. Unlike other data-analysis algorithms, it requires null or limited user expertise as all of its steps are unsupervised and solely entrusted to mathematical objective functions, without any hyperparameter tuning step required
Physics-based reduced-order modeling of flash-boiling sprays in the context of internal combustion engines
No full textFlash-boiling injection is one of the most effective ways to accomplish improved atomization compared to the high-pressure injection strategy. The tiny droplets formed via flash-boiling lead to fast fuel-air mixing and can subsequently improve combustion performance in engines. Most of the previous studies related to the topic focused on modeling flash-boiling sprays using three-dimensional (3D) computational fluid dynamics (CFD) techniques such as direct numerical simulations (DNS), large-eddy simulations (LES), and Reynolds-averaged Navier-Stokes (RANS) simulations. However, reduced order models can have significant advantages for applications such as the design of experiments, screening novel fuel candidates, and creating digital twins, for instance, because of the lower computational cost. In this study, the previously developed cross-sectionally averaged spray (CAS) model is thus extended for use in simulations of flash-boiling sprays. The present CAS model incorporates several physical submodels in flash-boiling sprays such as those for air entrainment, drag, superheated droplet evaporation, flash-boiling induced breakup, and aerodynamic breakup models. The CAS model is then applied to different fuels to investigate macroscopic spray characteristics such as liquid and vapor penetration lengths under flash-boiling conditions. It is found that the newly developed CAS model captures the trends in global flash-boiling spray characteristics reasonably well for different operating conditions and fuels. Moreover, the CAS model is shown to be faster by up to four orders of magnitude compared with simulations of 3D flash-boiling sprays. The model can be useful for many practical applications as a reduced-order flash-boiling model to perform low-cost computational representations of higher-order complex phenomena
Analysis of turbulent reacting jets via principal component analysis
No full textThe interpretation of high-dimensional data, like those obtained from Direct Numerical Simulations (DNS) of turbulent reacting flows, constitutes one of the biggest challenges in science and engineering. Although these simulations are a source of key information to advance the knowledge of turbulent combustion, as well as to develop and validate modeling approaches, the dimensionality of the data often limits the full opportunity to leverage the detailed and comprehensive information stored in datasets. The Principal Component Analysis (PCA) and its local formulation (LPCA) are widely used in many fields, including combustion. During the last 20 years, they have been used in combustion for the identification of lowdimensional manifolds, data analysis, and development of reduced-order models. Lower dimensional structures, either global or local, can provide better insights on the underlying physical phenomena, and lead to the formulation of high-fidelity models. This chapter aims to offer to the reader a comprehensive introduction of the PCA potential for data analysis, firstly introducing the main theoretical concepts, and then going through all the required computational steps by means of a MATLAB® code. Finally, the methodology is applied to data obtained from a DNS of a turbulent reacting non-premixed n-heptane jet in air. The latter can be regarded as an optimal case for data analysis because of the complex physics characterized by turbulence- chemistry interaction and soot formation
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
Torlak clitic doubling: A cross-linguistic comparison
Full text linkThis paper examines the types of clitics and clitic placement in Torlak. This vernacular, spoken in South-Eastern Serbia, also called the Prizren-Timok variety, whose genealogical position is still debatable, requires more attention from the scientific community. In this article, I describe clitic constructions, particularly the ones of clitic doubling and word order in Torlak by presenting data collected in the area of Trgovište and comparing it to the description of Bulgarian provided in Krapova & Cinque (2008). A further crosslinguistic comparison with Serbo-Croatian, Bulgarian, and Macedonian gives an insight into the relatedness of Torlak to the two typologically different areas: a Balkan Slavic and a non-Balkan Slavic one. This is particularly interesting since Torlak has clitic doubling, which makes it similar to Bulgarian and Macedonian, but it has second-position clitics, which makes it similar to Serbo-Croatian, thereby challenging certain cross-linguistic generalizations of Bošković (2001; 2004a,b; 2007; 2016). The overall results allow us to have a clearer picture of the use of clitics in this non-standard variety
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
- …
