A pure jump Markov process with a random singularity spectrum

We construct a non-decreasing pure jump Markov process, whose jump measure heavily depends on the values taken by the process. We determine the singularity spectrum of this process, which turns out to be random and to depend locally on the values taken by the process. The result relies on fine properties of the distribution of Poisson point processes and on ubiquity theorems.Comment: 20 pages, 4 figure

Time-accurate anisotropic mesh adaptation for three-dimensional time-dependent problems with body-fitted moving geometries

International audienceAnisotropic metric-based mesh adaptation has proved its efficiency to reduce the CPU time of steady and unsteady simulations while improving their accuracy. However, its extension to time-dependent problems with body-fitted moving geometries is far from straightforward. This paper establishes a well-founded framework for multiscale mesh adaptation of unsteady problems with moving boundaries. This framework is based on a novel space–time analysis of the interpolation error, within the continuous mesh theory. An optimal metric field, called ALE metric field, is derived, which takes into account the movement of the mesh during the adaptation. Based on this analysis, the global fixed-point adaptation algorithm for time-dependent simulations is extended to moving boundary problems, within the range of body-fitted moving meshes and ALE simulations. Finally, three dimensional adaptive simulations with moving boundaries are presented to validate the proposed approach

First benchmark of the Unstructured Grid Adaptation Working Group

Unstructured grid adaptation is a technology that holds the potential to improve the automation and accuracy of computational fluid dynamics and other computational disciplines. Difficulty producing the highly anisotropic elements necessary for simulation on complex curved geometries that satisfies a resolution request has limited this technology's widespread adoption. The Unstructured Grid Adaptation Working Group is an open gathering of researchers working on adapting simplicial meshes to conform to a metric field. Current members span a wide range of institutions including academia, industry, and national laboratories. The purpose of this group is to create a common basis for understanding and improving mesh adaptation. We present our first major contribution: a common set of benchmark cases, including input meshes and analytic metric specifications, that are publicly available to be used for evaluating any mesh adaptation code. We also present the results of several existing codes on these benchmark cases, to illustrate their utility in identifying key challenges common to all codes and important differences between available codes. Future directions are defined to expand this benchmark to mature the technology necessary to impact practical simulation workflows

Carreaux Bézier-Serendip de degré arbitraire

We define B\'ezier-Serendipity patches for quads and hexes with full symmetry properties. We give a way of constructing those patches by considering the B\'ezier setting. We show that, since the degree~5, the lack of symmetry for the Serendipity Lagrange finite elements remains a point for our patches and we show that after adding an adequate number of additional control points, we can achieve this symmetry.On d\'efinit des carreaux dits de B\'ezier-Serendip compl\`etement sym\'etriques pour les g\'eom\'etries quadrilat\`erales et hexa\`edriques. On montre comment les construire en travaillant directement sur une \'ecriture dans la base des polyn\^omes de Bernstein. On donne ainsi l'expression de leurs polyn\^omes de base dans le monde B\'ezier. On indique que d\`es le degr\'e 5, le probl\`eme de sym\'etrie rencontr\'e dans les \'el\'ements finis Serendip classiques se retrouve ici. On montre alors qu'en ajoutant judicieusement des points de contr\^ole suppl\'ementaires, on peut retrouver une solution sym\'étriqué

Construction et validation des éléments réduits associés á un carreau simplicial de degré arbitraire

We give a method to constructing Lagrange Serendipity (or reduced) simplices with a detailed description of the triangles of degree 3 and 4. We indicate that higher order triangles are not candidate apart if we impose a restricted polynomial space. We show that a tetrahedron of degree 3 is a candidate while high order elements are not candidate even if a restriction in the polynomial space is considered. In addition, we propose a method for the validation of such elements, in a given mesh, where the validation means the positiveness of the jacobianOn montre comment construire les éléments finis de Lagrange simpliciaux "Serendip" ou plutôt réduits en détaillant le cas des triangles de degré 3 et 4 et on indique qu'il n'y a probablemen pas de tels éléments pour les degrés supérieurs sauf á se restreindre sur l'espace polynomial cherché. On regarde également le cas des tétraédres en montrant qu'il y a un élément Serendip (ou réduit) au degré 3 mais pas au dela même avec la restriction indiquée ci-dessus. On indique également comment s'assurer que le jacobien de ces éléments, dans un maillage donné, soit positif partou

Construction et validation des éléments Serendip associés á un carreau de degré arbitraire

We give a method to constructing Serendipity elements for quads and hexes with full symmetry properties and indicate the reading of their shape functions. We show that, since the degree~5, the Serendipity elements are no longer symmetric but we propose a method resulting in a Lagrange element of degree 5 with full symmetry properties after adding an adequate number of additional nodes. On the other hand, we show how to guarantee the geometric validity of a given curved element (seen as a patch) of a mesh. This is achieved after writing the patch in a Bézier setting (Bernstein polynomials and control points). In addition, we discuss the case of patch derived from a transfinite interpolation and it is proved that only some of them are Serendipity elements indeed, we return to the same elements as above.On montre comment construire des éléments Serendip complétement symétriques basés sur un produit tensoriel (quadrilatéres et hexaédres) et on donne l'expression de leurs fonctions de forme. On indique que dés le degré 5, les éléments Serendip classiques ne sont plus symétriques mais que l'on peut construire des éléments (de Lagrange) complétement symétriques en ajoutant judicieusement des n{\oe}uds supplémentaires. Par ailleurs, on indique comment valider géométriquement un élément courbe (vu comme un carreau) d'un maillage donné défini de cette fa\c con. Cette validation se fait en raisonnant sur l'écriture des carreaux dans le formalisme Bézier (polynôme de Bernstein et points de contrôle). On discute ensuite des carreaux définis par interpolation transfinie et on montre que certains d'entre eux sont les mêmes que ceux obtenus précédemment et, ainsi, ont la propriété de Serendipité

Unstructured Grid Adaptation and Solver Technology for Turbulent Flows

Unstructured grid adaptation is a tool to control Computational Fluid Dynamics (CFD) discretization error. However, adaptive grid techniques have made limited impact on production analysis workflows where the control of discretization error is critical to obtaining reliable simulation results. Issues that prevent the use of adaptive grid methods are identified by applying unstructured grid adaptation methods to a series of benchmark cases. Once identified, these challenges to existing adaptive workflows can be addressed. Unstructured grid adaptation is evaluated for test cases described on the Turbulence Modeling Resource (TMR) web site, which documents uniform grid refinement of multiple schemes. The cases are turbulent flow over a Hemisphere Cylinder and an ONERA M6Wing. Adaptive grid force and moment trajectories are shown for three integrated grid adaptation processes with Mach interpolation control and output error based metrics. The integrated grid adaptation process with a finite element (FE) discretization produced results consistent with uniform grid refinement of fixed grids. The integrated grid adaptation processes with finite volume schemes were slower to converge to the reference solution than the FE method. Metric conformity is documented on grid/metric snapshots for five grid adaptation mechanics implementations. These tools produce anisotropic boundary conforming grids requested by the adaptation process

Verification of Unstructured Grid Adaptation Components

Adaptive unstructured grid techniques have made limited impact on production analysis workflows where the control of discretization error is critical to obtaining reliable simulation results. Recent progress has matured a number of independent implementations of flow solvers, error estimation methods, and anisotropic grid adaptation mechanics. Known differences and previously unknown differences in grid adaptation components and their integrated processes are identified here for study. Unstructured grid adaptation tools are verified using analytic functions and the Code Comparison Principle. Three analytic functions with different smoothness properties are adapted to show the impact of smoothness on implementation differences. A scalar advection-diffusion problem with an analytic solution that models a boundary layer is adapted to test individual grid adaptation components. Laminar flow over a delta wing and turbulent flow over an ONERA M6 wing are verified with multiple, independent grid adaptation procedures to show consistent convergence to fine-grid forces and a moment. The scalar problems illustrate known differences in a grid adaptation component implementation and a previously unknown interaction between components. The wing adaptation cases in the current study document a clear improvement to existing grid adaptation procedures. The stage is set for the infusion of verified grid adaptation into production fluid flow simulations

Tracking and synchronization of the yeast cell cycle using dielectrophoretic opacity

Cell cycle synchronization is an important tool for the study of the cell division stages and signalling. It provides homogeneous cell cultures that are of importance to develop and improve processes such as protein synthesis and drug screening. The main approach today is the use of metabolic agents that block the cell cycle at a particular phase and accumulate cells at this phase, disturbing the cell physiology. We provide here a non-invasive and label-free continuous cell sorting technique to analyze and synchronize yeast cell division. By balancing opposing dielectrophoretic forces at multiple frequencies, we maximize sensitivity to the characteristic shape and internal structure changes occurring during the yeast cell cycle, allowing us to synchronize the culture in late anaphase