Positivity of flux vector splitting schemes

Over the last ten years, robustness of schemes has raised an increasing interest among the CFD community. One mathematical aspect of scheme robustness is the positivity preserving property. At high Mach numbers, solving the conservative Euler equations can lead to negative densities or internal energy. Some schemes such as the flux vector splitting (FVS) schemes are known to avoid this drawback. In this study, a general method is detailed to analyze the positivity of FVS schemes. As an application, three classical FVS schemes (Van Leer's, Hänel's variant, and Steger and Warming's) are proved to be positively conservative under a CFL-like condition. Finally, it is proved that for any FVS scheme, there is an intrinsic incompatibility between the desirable property of positivity and the exact resolution of contact discontinuities

Detection and characterisation of genes encoding antibiotic resistance in the cultivable oral microflora.

The emergence of antibiotic-resistant bacteria has become a major threat to public health. The increased use of antibiotics has selected for the dissemination of antibiotic resistance genes between organisms from different species and different genera. There is a large body of evidence that the indigenous microbiota can act as a reservoir of antibiotic-resistant bacteria. However little is known about the molecular basis for this in bacteria from the oral cavity. Therefore the aim of this work was to determine the prevalence of antibiotic-resistant bacteria and antibiotic resistance genes in the cultivable oral microbiota. Saliva and plaque samples were taken from each of 60 healthy adults who had not taken any antibiotics during the previous three months. Each sample was plated onto antibiotic-containing media to quantitate and identify antibiotic-resistant strains. All of the individuals harboured bacteria resistant to erythromycin, gentamicin, vancomycin and tetracycline. Only 4 individuals (7%) did not have any cultivable bacteria resistant to amoxycillin. Oral bacteria resistant to gentamicin were the most commonly isolated (constituting 23% of total cultivable oral bacteria) followed by erythromycin (18% of the total viable count), vancomycin (16% of the total viable count), tetracycline (10% of the total viable count) and amoxycillin (4% of the total viable count). Multiply-resistant bacteria were found with 55% of tetracycline-resistant isolates being resistant also to erythromycin and 6% resistant also to both amoxycillin and erythromycin. The most prevalent genes encoding tetracycline and erythromycin resistance were tet(M), tet(W), tet(0), and mef and erm(B) respectively. In some cases, tet(M) and ermB were contained within a Tn/5 5-like conjugative transposon and could be co-tranferred to Enterococcus faecalis. Finally the nature of the genetic support for one of the tet(W) genes, was determined and found to be flanked by two transposases belonging to two different families of insertion sequences (IS30 and IS256). This element was highly unstable in E. coli. This study showed that antibiotic-resistant bacteria and antibiotic resistance genes are present in the oral microbiota and that oral bacteria are likely to play an important role in the evolution and dissemination of antibiotic resistance genes

Mill-cut: a neural network system for the prediction of thermo-mechanical loads induced in end-milling operations

This paper presents the design and implementation issues of a generalized system called mill-cut, developed for the prediction of cutting forces and temperature in end-milling operations. Based on an ANN approach, mill-cut predicts all the three components of cutting forces and average shear plane temperature for a given set of machining parameters broadly categorized into three groups viz. (i) cutting tool geometrical parameters (ii) cutting parameters and (iii) workpiece material properties. In the present work, for representing overall machining condition, 15 machining parameters having major impact on the cutting forces and cutting temperature were chosen. The feed-forward back-propagated ANN architecture has been incorporated, which was initially trained with analytical data before incorporating it as part of an integrated system. Results obtained from the proposed model show good agreement with the experimental/numerical (FEM based) results available in the literatur

Two Dimensional Model of an Electro-Thermal Ice Protection System

In this communication we shall focus on the main governing equations and building blocks of the M.A.D (Anti-icing Deicing Modelling) numerical tool, which is now renamed as INUIT (Integrated NUmerical model of Ice protection sysTems) and part of the new generation of ONERA icing codes. The code simulates the functioning of an electro-thermal de-icing system. We shall also discuss the various improvements and new features we have added, especially a mechanical model of the ice block in order to improve the ice-shedding criterion

Monte-Carlo simulation of colliding particles or coalescing droplets transported by a turbulent flow in the framework of a joint fluid–particle pdf approach

The aim of the paper is to introduce and validate a Monte-Carlo algorithm for the prediction of an ensemble of colliding solid particles, or coalescing liquid droplets, suspended in a turbulent gas flow predicted by Reynolds Averaged Navier Stokes approach (RANS). The new algorithm is based on the direct discretization of the collision/coalescence kernel derived in the framework of a joint fluid–particle pdf approach proposed by Simonin et al. (2002). This approach allows to take into account correlations between colliding inertial particle velocities induced by their interaction with the fluid turbulence. Validation is performed by comparing the Monte-Carlo predictions with deterministic simulations of discrete solid particles coupled with Direct Numerical Simulation (DPS/DNS), or Large Eddy Simulation (DPS/LES), where the collision/coalescence effects are treated in a deterministic way. Five cases are investigated: elastic monodisperse particles, non-elastic monodisperse particles, binary mixture of elastic particles and binary mixture of elastic settling particles in turbulent flow and finally coalescing droplets. The predictions using the new Monte-Carlo algorithm are in much better agreement with DPS/DNS results than the ones using the standard algorithm

A CONSERVATIVE SAINT-VENANT TYPE MODEL TO DESCRIBE THE DYNAMICS OF THIN PARTIALLY WETTING FILMS WITH REGULARIZED FORCES AT THE CONTACT LINE

This paper deals with the numerical simulation of thin liquid films flowing on partially wetting solid substrates. A 2D Saint-Venant like model is proposed. Its originality lies in the conservative formulation of the capillary forces and in the model used for the disjoining pressure that accounts for the contact line capillary forces. A finite volume scheme is proposed for the resolution of the system and various numerical examples are presented and discussed. In particular, when the mesh resolution is fine enough, the model is proved to be able to predict correctly the spreading of a film with the exact contact angle in the vicinity of the contact line. When the mesh size is larger than the film thickness (which could be the case for many industrial applications), it is of course no longer possible to recover the contact angle. However, the model is proved to correctly predict the spreading of the film. This important feature is related to the thermodynamic consistency of the model in the sense that the latter ensures by construction the decrease of the film total free energy in the absence of external driving forces

MySemCloud: Semantic-aware Word Cloud Editing

Word clouds are a popular text visualization technique that summarize an input text by displaying its most important words in a compact image. The traditional layout methods do not take proximity effects between words into account; this has been improved in semantic word clouds, where relative word placement is controlled by edges in a word similarity graph. We introduce MySemCloud, a new human-in-the-loop tool to visualize and edit semantic word clouds. MySemCloud lets users perform computer-assisted local moves of words, which improve or at least retain the semantic quality. To achieve this, we construct a word similarity graph on which a system of forces is applied to generate a compact initial layout with good semantic quality. The force system also allows us to maintain these attributes after each user interaction, as well as preserve the user's mental map. The tool provides algorithmic support for the editing operations to help the user enhance the semantic quality of the visualization, while adjusting it to their personal preference. We show that MySemCloud provides high user satisfaction as well as permits users to create layouts of higher quality than state-of-the-art semantic word cloud generation tools.Comment: Appeared at PacificVis 202

Theory and validation of a 2D Finite-Volume integral boundary layer method intended for icing applications

International audienceA two-dimensional integral boundary layer method is developed to enable fast and economical computations of boundary layer flows. The ultimate goal is to provide some experience for the extension of this method in three dimensions. In this study, the unsteady momentum and kinetic energy integral equations are solved numerically, together with a set of closure relations based on assumed velocity profiles for laminar and turbulent flows. The robustness of the method is ensured by a Finite-Volume formulation based on an upwind scheme and a semi-implicit time discretization. The accuracy of the numerical method in the vicinity of the stagnation point is strongly improved by introducing a consistent corrective source term in the right-hand side of the equation system. The chosen closure relations are validated with test cases of self-similar flows. Numerical results are also compared with those of a full Prandtl equations code for NACA0012, GLC305 and MS317 airfoils test cases to demonstrate the capabilities of the method. Finally, preliminary results are shown proving the ability of the method to deal with iced airfoils even for complex glaze ice shapes.Une méthode bidimensionnelle de couche limite intégrale est développée pour permettre des calculs rapides et économiques des écoulements de couche limite. L'objectif est de fournir une certaine expérience pour l'extension de cette méthode en trois dimensions. Dans cette étude, les équations intégrales instationnaires de la quantité de mouvement et de l'énergie cinétique sont résolues numériquement, ainsi qu'un ensemble de relations de fermeture basées sur des profils de vitesse supposés pour des écoulements laminaires et turbulents. La robustesse de la méthode est assurée par une formulation aux Volumes Finis, basée sur un schéma de décentré amont et une discrétisation semi-implicite du temps. De plus, une méthode de contrôle a été développée afin d'éviter la singularité de Goldstein. La précision de la méthode numérique au voisinage du point d'arrêt est très élevée et améliorée par l'introduction d'un terme source correctif au second membre du système d'équations. Les relations de fermeture choisies sont validées avec des cas-test d'écoulements auto-similaires. Les résultats numériques sont également comparés à ceux d'une résolution des équations de Prandtl pour des cas-tests sur profils NACA0012, GLC305 et MS317 afin de démontrer les capacités de la méthode. Enfin, des résultats préliminaires sont présentés prouvant la capacité de la méthode à traiter des profils givrés, même pour les formes complexes de givre

On the use of a 2D Finite-Volume Integral Boundary Layer Method for Ice Accretion Calculations

In this paper, a two-dimensional integral boundary layer method developed in a recent work is applied to ice accretion computations. The method has already been validated in terms of boundary layer dynamic effects in another article. It is here validated for its ability to capture ice shapes, once the method is included in an icing suite. To be more specific, results using the new boundary layer method are compared against experimental ice shapes and simulated ones with the widely-used simplified integral method. The validation is carried out at an aggregated level because icing databases generally provide access to final ice shapes only. But since the simplified integral method is used in many icing numerical tools, this comparison makes it possible to investigate the benefits of introducing the new method for calculating the boundary layer. The main outcome of the new method is an improvement of the prediction of the boundary layer prediction under smooth-wall assumption, which in turn improves ice shape prediction. It is shown that, overall, the ice shapes are indeed either better predicted with the new method than with the baseline approach, or equally predicted with both methods. In addition, since the heat transfer coefficient tends to be underestimated by simplified integral methods, the new approach tends to predict lower horn angles than the baseline approach. Finally, the consequences of these results on current and future developments of ice accretion solvers are discussed. In particular, the new method is better suited to a 3D extension than the simplified integral method