Dynamic p-enrichment schemes for multicomponent reactive flows

We present a family of p-enrichment schemes. These schemes may be separated into two basic classes: the first, called \emph{fixed tolerance schemes}, rely on setting global scalar tolerances on the local regularity of the solution, and the second, called \emph{dioristic schemes}, rely on time-evolving bounds on the local variation in the solution. Each class of $p$-enrichment scheme is further divided into two basic types. The first type (the Type I schemes) enrich along lines of maximal variation, striving to enhance stable solutions in "areas of highest interest." The second type (the Type II schemes) enrich along lines of maximal regularity in order to maximize the stability of the enrichment process. Each of these schemes are tested over a pair of model problems arising in coastal hydrology. The first is a contaminant transport model, which addresses a declinature problem for a contaminant plume with respect to a bay inlet setting. The second is a multicomponent chemically reactive flow model of estuary eutrophication arising in the Gulf of Mexico.Comment: 29 pages, 7 figures, 3 table

Viscous Shock Capturing in a Time-Explicit Discontinuous Galerkin Method

We present a novel, cell-local shock detector for use with discontinuous Galerkin (DG) methods. The output of this detector is a reliably scaled, element-wise smoothness estimate which is suited as a control input to a shock capture mechanism. Using an artificial viscosity in the latter role, we obtain a DG scheme for the numerical solution of nonlinear systems of conservation laws. Building on work by Persson and Peraire, we thoroughly justify the detector's design and analyze its performance on a number of benchmark problems. We further explain the scaling and smoothing steps necessary to turn the output of the detector into a local, artificial viscosity. We close by providing an extensive array of numerical tests of the detector in use.Comment: 26 pages, 21 figure

HDG-NEFEM with Degree Adaptivity for Stokes Flows

This paper presents the first degree adaptive procedure able to directly use the geometry given by a CAD model. The technique uses a hybridisable discontinuous Galerkin discretisation combined with a NURBS-enhanced rationale, completely removing the uncertainty induced by a polynomial approximation of curved boundaries that is common within an isoparametric approach. The technique is compared against two strategies to perform degree adaptivity currently in use. This paper demonstrates, for the first time, that the most extended technique for degree adaptivity can easily lead to a non-reliable error estimator if no communication with CAD software is introduced whereas if the communication with the CAD is done, it results in a substantial computing time. The proposed technique encapsulates the CAD model in the simulation and is able to produce reliable error estimators irrespectively of the initial mesh used to start the adaptive process. Several numerical examples confirm the findings and demonstrate the superiority of the proposed technique. The paper also proposes a novel idea to test the implementation of high-order solvers where different degrees of approximation are used in different elements

Cerclages à chaud et thérapeutiques du col uterin (résultats et étude des facteurs pronostiques)

OBJECTIF : Décrire les résultats et déterminer les facteurs prédictifs des cerclages à chaud et thérapeutiques. METHODE : Il s'agit d'une étude de cohorte rétrospective sur une période de 10 ans environ regroupant 46 patientes ayant eu un cerclage thérapeutique ou à chaud du col utérin avant 26 SA. Les critères de jugement étaient l'âge gestationnel à l'accouchement et le délai entre le cerclage et l'accouchement. Les facteurs pronostiques étudiés correspondaient à des caractéristiques maternelles, des données cliniques, échographiques et biologiques et aux modalités de prise en charge thérapeutique des patientes. RESULTATS : 46 patientes, incluant 15 grossesses gémellaires, ont été incluses dans l'étude. L'âge gestationnel moyen d'accouchement était de 34 SA et 4 jours avec 35 % d'accouchement prématuré avant 34 SA. Le délai moyen entre le cerclage et l'accouchement était de 93 jours. La réalisation d'un cerclage à chaud, la constatation d'une longueur cervicale efficace échographique inférieure ou égale à 5 mm et les cerclages sur grossesse gémellaire étaient des facteurs de risque d'échec des cerclages sur col modifié. CONCLUSION : Etant donné le risque de fausse-couche tardive ou d'accouchement très prématuré en cas de modifications cervicales au deuxième trimestre de la grossesse, la réalisation d'un cerclage thérapeutique ou à chaud semble bénéfique. Les facteurs de risque d'échec sont les modifications cervicales avancées et les cerclages sur grossesse gémellaire.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Workshop on numerical and physical modelling in multiphase flowsa cross-fertilization approach

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Méthodes de Galerkine discontinu d'ordre élevé pour la simulation instationnaire en maillage non structuré

BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

CFD simulations of large-scale reorganizations in PWR rod bundle flows

International audienceA coolant flow is used in Pressurized-Water Reactors (PWR) cores to extract the heat generated by nuclear reactions. Its temperature must be as homogeneous as possible in order to avoid a localized boiling, which would deteriorate the behaviour of the reactor. This flow is injected in the interstices of rod bundles, which namely are arrays of cylinders held together by support grids. While the initial velocity flow field is mostly aligned with the cylinder axes, mixing vanes are placed on the support grids in order to vastly increase inter-channel velocities and thus improve the overall thermal mixing. As depicted inthe sketch in figure 1, large-scale structures are generated in cross-section planes orthogonal to the rod axes in the wake of the mixing grid, and their layout as well as their evolution downstream of the grids have a large impact on the flow boiling margin. A thorough investigation of these coolant flow large-scale structures thus constitutes a key element of PWR safetyanalyses.Both experiments and Computational Fluid Dynamics (CFD) simulations have been used regularly in the last decades to investigate these large-scale flow structures. Notable experiments include the AGATE facility operated at the CEA Grenoble [3] as well as the OECD/NEA-KAERI benchmark test [2]. An example of a large-scale cross-flow pattern observed in the 5x5 rod bundle flow of the AGATE facility is shown in figure 2. Interestingly, this pattern spontaneously reorganized itself in thefar wake of the mixing grid so as to rotate from a mostly 45 and#9702; angle to a 135 and#9702; one. This phenomenon can be related to earlier observations of a pattern change in the wake of a mixing grid by Shen et al. [4], therein dubbed as a velocity inversion. In addition to the results obtained by Bieder et al. [1], CFD simulations of rod bundle flows based on a Large-Eddy Simulation (LES) sub-grid scale model have been performed, both in a reduced 3x3 rod bundle and in a 5x5 one, with the aim of reproducing such experimental large-scale reorganizations of the cross-section flow.Furthermore, a method of coupling between the 3D axial coordinate and the time variable through the Taylor frozen turbulence hypothesis is being used to advance a physical explanation to the large-scale reorganization phenomena. 2DDirect Numerical Simulations (DNS) have thus been performed in rod bundle cross-section geometries from an initial condition based on a 2D slice of the 3D flow in the immediate wake of the grid in LES simulations. A comparison between the evolution over time of the 2D simulated flow in a cross-section geometry and the axial evolution of a steady 3D flow cross-section is then carried out, revealing interesting parallels

Minimum enstrophy states and bifurcations in 2D Euler flows within an annular domain

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