scholarly journals Direct numerical simulation of the autoignition of a hydrogen plume in a turbulent coflow of hot air

2013 ◽  
Vol 720 ◽  
pp. 424-456 ◽  
Author(s):  
S. G. Kerkemeier ◽  
C. N. Markides ◽  
C. E. Frouzakis ◽  
K. Boulouchos
Keyword(s):  
Complex Dynamics ◽  
Mixture Fraction ◽  
A Priori ◽  
Three Dimensional ◽  
Scalar Dissipation ◽  
Detailed Chemistry ◽  
History Of ◽  
Reactive Mixture ◽  
Set Up ◽  
Flame Sheet

AbstractThe autoignition of an axisymmetric nitrogen-diluted hydrogen plume in a turbulent coflowing stream of high-temperature air was investigated in a laboratory-scale set-up using three-dimensional numerical simulations with detailed chemistry and transport. The plume was formed by releasing the fuel from an injector with bulk velocity equal to that of the surrounding air coflow. In the ‘random spots’ regime, autoignition appeared randomly in space and time in the form of scattered localized spots from which post-ignition flamelets propagated outwards in the presence of strong advection. Autoignition spots were found to occur at a favourable mixture fraction close to the most reactive mixture fraction calculated a priori from considerations of homogeneous mixtures based on inert mixing of the fuel and oxidizer streams. The value of the favourable mixture fraction evolved in the domain subject to the effect of the scalar dissipation rate. The hydroperoxyl radical appeared as a precursor to the build-up of the radical pool and the ensuing thermal runaway at the autoignition spots. Subsequently, flamelets propagated in all directions with complex dynamics, without anchoring or forming a continuous flame sheet. These observations, as well as the frequency of and scatter in appearance of the spots, are in good agreement with experiments in a similar set-up. In agreement with experimental observations, an increase in turbulence intensity resulted in a downstream shift of autoignition. An attempt is made to understand the key processes that control the mean axial and radial locations of the spots, and are responsible for the observed scatter. The advection of the most reactive mixture through the domain, and hence the history of evolution of the developing radical pools were considered to this effect.

scholarly journals Assessing biases, relaxing moralism: On ground-truthing practices in machine learning design and application

2021 ◽  
Vol 8 (1) ◽  
pp. 205395172110135
Author(s):  
Florian Jaton
Keyword(s):  
Machine Learning ◽  
William James ◽  
A Priori ◽  
Learning Algorithms ◽  
Three Dimensional ◽  
Ground Truth ◽  
Machine Learning Algorithms ◽  
Ground Truthing ◽  
Set Up ◽  
The Moment

This theoretical paper considers the morality of machine learning algorithms and systems in the light of the biases that ground their correctness. It begins by presenting biases not as a priori negative entities but as contingent external referents—often gathered in benchmarked repositories called ground-truth datasets—that define what needs to be learned and allow for performance measures. I then argue that ground-truth datasets and their concomitant practices—that fundamentally involve establishing biases to enable learning procedures—can be described by their respective morality, here defined as the more or less accounted experience of hesitation when faced with what pragmatist philosopher William James called “genuine options”—that is, choices to be made in the heat of the moment that engage different possible futures. I then stress three constitutive dimensions of this pragmatist morality, as far as ground-truthing practices are concerned: (I) the definition of the problem to be solved (problematization), (II) the identification of the data to be collected and set up (databasing), and (III) the qualification of the targets to be learned (labeling). I finally suggest that this three-dimensional conceptual space can be used to map machine learning algorithmic projects in terms of the morality of their respective and constitutive ground-truthing practices. Such techno-moral graphs may, in turn, serve as equipment for greater governance of machine learning algorithms and systems.

A brief history of the filling simulation of injection moulding

2008 ◽  
Vol 223 (3) ◽  
pp. 711-721 ◽  
Author(s):  
D Cardozo
Keyword(s):  
Computer Simulation ◽  
Injection Moulding ◽  
Three Dimensional ◽  
History Of ◽  
Dimensional Models ◽  
Three Dimensional Models ◽  
Set Up ◽  
Filling Simulation ◽  
Basic Features ◽  
Plastic Parts

Injection moulding is one of the most important manufacturing processes for mass production of complex plastic parts. The quality of injection moulded parts depends not only on the material, shape, and function of the part design, but also on how the material is processed during moulding. Traditional design approaches based on intuition, prior experience, and trial-and-error methodology have been becoming less efficient and effective. With advances in numerical modelling and computer simulation techniques, there have been tremendous efforts made to develop computer simulation tools to facilitate injection moulding design and process set-up. This paper reviews the history of research and development in the filling simulation of injection moulding. The existing models are classified into three categories: one-dimensional models, 2.5D models, and three-dimensional models. The basic features and relative key techniques about these models have been discussed. The techniques of tacking the moving flow front have also been presented. It is then followed by conclusions and discussions of these mentioned models.

scholarly journals Brain MRI Segmentation with Multiphase Minimal Partitioning: A Comparative Study

2007 ◽  
Vol 2007 ◽  
pp. 1-15 ◽  
Author(s):  
Elsa D. Angelini ◽  
Ting Song ◽  
Brett D. Mensh ◽  
Andrew F. Laine
Keyword(s):  
Quantitative Evaluation ◽  
Level Set ◽  
Markov Random Fields ◽  
Initial Conditions ◽  
A Priori ◽  
Brain Mri ◽  
Three Dimensional ◽  
Error Rates ◽  
Adult Brain ◽  
Set Up

This paper presents the implementation and quantitative evaluation of a multiphase three-dimensional deformable model in a level set framework for automated segmentation of brain MRIs. The segmentation algorithm performs an optimal partitioning of three-dimensional data based on homogeneity measures that naturally evolves to the extraction of different tissue types in the brain. Random seed initialization was used to minimize the sensitivity of the method to initial conditions while avoiding the need fora prioriinformation. This random initialization ensures robustness of the method with respect to the initialization and the minimization set up. Postprocessing corrections with morphological operators were applied to refine the details of the global segmentation method. A clinical study was performed on a database of 10 adult brain MRI volumes to compare the level set segmentation to three other methods: “idealized” intensity thresholding, fuzzy connectedness, and an expectation maximization classification using hidden Markov random fields. Quantitative evaluation of segmentation accuracy was performed with comparison to manual segmentation computing true positive and false positive volume fractions. A statistical comparison of the segmentation methods was performed through a Wilcoxon analysis of these error rates and results showed very high quality and stability of the multiphase three-dimensional level set method.

scholarly journals Falling styles of disks

2013 ◽  
Vol 719 ◽  
pp. 388-405 ◽  
Author(s):  
Franck Auguste ◽  
Jacques Magnaudet ◽  
David Fabre
Keyword(s):  
Complex Dynamics ◽  
Three Dimensional ◽  
Relative Magnitude ◽  
The Body ◽  
Fluid Inertia ◽  
Viscous Effects ◽  
Fluid Medium ◽  
Body Experiences ◽  
Set Up ◽  
Thin Disks

AbstractWe numerically investigate the dynamics of thin disks falling under gravity in a viscous fluid medium at rest at infinity. Varying independently the density and thickness of the disk reveals the influence of the disk aspect ratio which, contrary to previous belief, is found to be highly significant as it may completely change the route to non-vertical paths as well as the boundaries between the various path regimes. The transition from the straight vertical path to the planar fluttering regime is found to exhibit complex dynamics: a bistable behaviour of the system is detected within some parameter range and several intermediate regimes are observed in which, although the wake is unstable, the path barely deviates from vertical. By varying independently the body-to-fluid inertia ratio and the relative magnitude of inertial and viscous effects over a significant range, we set up a comprehensive map of the corresponding styles of path followed by an infinitely thin disk. We observe the four types of planar regimes already reported in experiments but also identify two additional fully three-dimensional regimes in which the body experiences a slow horizontal precession superimposed onto zigzagging or tumbling motions.

An experimental study of recirculating flow through fluid–sediment interfaces

1999 ◽  
Vol 383 ◽  
pp. 229-247 ◽  
Author(s):  
A. KHALILI ◽  
A. J. BASU ◽  
U. PIETRZYK ◽  
M. RAFFEL
Keyword(s):  
Fluid Layer ◽  
Saturated Porous Medium ◽  
A Priori ◽  
Three Dimensional ◽  
Solid Matrix ◽  
Permeable Sediments ◽  
Recirculating Flow ◽  
Positron Emission ◽  
Dye Transport ◽  
Set Up

We report here visualizations and quantitative measurements of scalar transport, under the influence of rotation, through permeable sediments with an overlying fluid layer. The experimental set-up considered here is a stationary cylinder containing a fluid-saturated porous medium up to its midheight, with supernatant water on top. A rotating lid generates, in the upper fluid region, a flow that partially percolates into the porous layer below. The velocity field in the fluid layer is obtained using particle image velocimetry (PIV). Further, dye transport from the sediment is studied using two different techniques. The first one is positron emission tomography (PET), a non-invasive method which allowed us to ‘see’ through the opaque solid matrix, and to obtain full three-dimensional pictures of dye transport through the sediment. The second one is digital photographic visualization from outside, and subsequent image processing in order to obtain the near-wall dye-washout depth. The experimental data suggest that the temporal evolution of washout depth for different sediments follows near-logarithmic behaviour. This finding is of importance for the a priori estimation of the transport of fluid and other solute substances in sandy aquatic sediments.

scholarly journals Consistent Conditional Moment Closure Modelling of a Lifted Turbulent Jet Flame Using the Presumedβ-PDF Approach

2014 ◽  
Vol 2014 ◽  
pp. 1-25 ◽  
Author(s):  
Ahmad El Sayed ◽  
Roydon A. Fraser
Keyword(s):  
Mixture Fraction ◽  
Turbulent Jet ◽  
Moment Closure ◽  
Scalar Dissipation ◽  
Conditional Moment ◽  
Jet Flame ◽  
Gradient Diffusion ◽  
Conditional Moment Closure ◽  
History Of ◽  
Closure Modelling

A liftedH2/N2turbulent jet flame issuing into a vitiated coflow is investigated using the conditional moment closure. The conditional velocity (CV) and the conditional scalar dissipation rate (CSDR) submodels are chosen such that they are fully consistent with the moments of the presumedβprobability density function (PDF). The CV is modelled using the PDF-gradient diffusion model. Two CSDR submodels based on the double integration of the homogeneous and inhomogeneous mixture fraction PDF transport equations are implemented. The effect of CSDR modelling is investigated over a range of coflow temperatures (Tc) and the stabilisation mechanism is determined from the analysis of the transport budgets and the history of radical build-up ahead of the stabilisation height. For allTc, the balance between chemistry, axial convection, and micromixing, and the absence of axial diffusion upstream of the stabilisation height indicate that the flame is stabilized by autoignition. This conclusion is confirmed from the rapid build-up ofHO2ahead ofH,O, andOH. The inhomogeneous CSDR modelling yields higher dissipation levels at the most reactive mixture fraction, which results in longer ignition delays and larger liftoff heights. The effect of the spurious sources arising from homogeneous modelling is found to be small but nonnegligible, mostly notably within the flame zone.

Three-Dimensional Direct Numerical Simulations of Autoignition in Turbulent Non-Premixed Flows With Simple and Complex Chemistry

2006 ◽  
Author(s):  
T. Lo̸va˚s ◽  
A. Lowe ◽  
R. S. Cant ◽  
E. Mastorakos
Keyword(s):  
Numerical Simulations ◽  
Mixture Fraction ◽  
Negative Temperature ◽  
Single Step ◽  
Direct Numerical Simulations ◽  
Spontaneous Ignition ◽  
Conditional Probability Density ◽  
Scalar Dissipation ◽  
Reactive Mixture ◽  
Complex Chemistry

3D Direct Numerical Simulations (DNS) of autoignition in turbulent non-premixed flows between fuel and hotter air have been carried out using both 1-step and complex chemistry consisting of a 22 species n-heptane mechanism to investigate spontaneous ignition timing and location. The simple chemistry results showed that the previous findings from 2D DNS that ignition occurred at the most reactive mixture fraction (ξMR) and at small values of the conditional scalar dissipation rate (N|ξMR) are valid also for 3D turbulent mixing fields. Performing the same simulation many times with different realizations of the initial velocity field resulted in a very narrow statistical distribution of ignition delay time, consistent with a previous conjecture that the first appearance of ignition is correlated with the low-N content of the conditional probability density function of N. The simulations with complex chemistry for conditions outside the Negative Temperature Coefficient (NTC) regime show behaviour similar to the single-step chemistry simulations. However, in the NTC regime, the most reactive mixture fraction is very rich and ignition seems to occur at high values of scalar dissipation.

Sea Urchins and Circuses: The Modernist Natural Histories of Jean Painlevé and Alexander Calder

2018 ◽  
Vol 13 (2) ◽  
pp. 187-211
Author(s):  
Patricia E. Chu
Keyword(s):  
New Media ◽  
Sea Urchins ◽  
Life Sciences ◽  
Three Dimensional ◽  
Machine Age ◽  
Avant Garde ◽  
History Of ◽  
And Performance ◽  
The One ◽  
Natural Historian

The Paris avant-garde milieu from which both Cirque Calder/Calder's Circus and Painlevé’s early films emerged was a cultural intersection of art and the twentieth-century life sciences. In turning to the style of current scientific journals, the Paris surrealists can be understood as engaging the (life) sciences not simply as a provider of normative categories of materiality to be dismissed, but as a companion in apprehending the “reality” of a world beneath the surface just as real as the one visible to the naked eye. I will focus in this essay on two modernist practices in new media in the context of the history of the life sciences: Jean Painlevé’s (1902–1989) science films and Alexander Calder's (1898–1976) work in three-dimensional moving art and performance—the Circus. In analyzing Painlevé’s work, I discuss it as exemplary of a moment when life sciences and avant-garde technical methods and philosophies created each other rather than being classified as separate categories of epistemological work. In moving from Painlevé’s films to Alexander Calder's Circus, Painlevé’s cinematography remains at the forefront; I use his film of one of Calder's performances of the Circus, a collaboration the men had taken two decades to complete. Painlevé’s depiction allows us to see the elements of Calder's work that mark it as akin to Painlevé’s own interest in a modern experimental organicism as central to the so-called machine-age. Calder's work can be understood as similarly developing an avant-garde practice along the line between the bestiary of the natural historian and the bestiary of the modern life scientist.

Formation and Development of the Pre-Professional Training System of Foreign Medical Applicants in Ukraine (Historical and Educational Aspect)

2014 ◽  
Vol 4 (3) ◽  
pp. 95-98
Author(s):  
Iana Proskurkina
Keyword(s):  
Foreign Students ◽  
Professional Training ◽  
Training System ◽  
Further Education ◽  
Effective System ◽  
History Of ◽  
Set Up ◽  
The University ◽  
History Of Formation ◽  
Educational Aspect

Abstract The growing number of foreign applicants looking forward to getting education in Ukrainian medical universities makes us find the ways how to improve and make effective the pre-professional training system of foreign medical applicants for further education. The article deals with the issues of the history of formation and development of the preprofessional training system of foreign medical applicants in Ukraine. On the ground of the electronic databases of the official websites of higher educational establishments, the data on years of opening first offices of the dean, departments and preparatory faculties for foreign medical applicants in Ukrainian medical universities are analyzed and systematized. Also the data on the setting up preparatory faculties at other universities who carry out licensed training of foreign students of the medical profile are presented. The data on the operating and management of such institutions in the system of the University administration are generalized. It’s revealed that during the years of its functioning the pre-professional training has changed, in particular the system was commercialized and the institutions involved in training foreign applicants have been reorganized. The modern trends in teaching foreign medical students at the preparatory faculties of the Ukrainian medical universities are displayed. Based on the analysis of the data it is concluded that the system of the pre-professional training of foreign medical applicants was set up in the 50s-60s years of the twentieth century. During this time, some positive experience in the preparation of future international medical specialists has been gained. The system of the pre-professional training of foreign medical applicants has been comprehensively improved and an effective system of managing foreign medical applicants has been created.

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