Search results for "numerical simulation"

Modeling multiple taxis: Tumor invasion with phenotypic heterogeneity, haptotaxis, and unilateral interspecies repellence

2021

We provide a short review of existing models with multiple taxis performed by (at least) one species and consider a new mathematical model for tumor invasion featuring two mutually exclusive cell phenotypes (migrating and proliferating). The migrating cells perform nonlinear diffusion and two types of taxis in response to non-diffusing cues: away from proliferating cells and up the gradient of surrounding tissue. Transitions between the two cell subpopulations are influenced by subcellular (receptor binding) dynamics, thus conferring the setting a multiscale character. We prove global existence of weak solutions to a simplified model version and perform numerical simulations for the full se…

A dynamic subgrid-scale tensorial eddy viscosity model

1999

In the Navier-Stokes equations the removal of the turbulent fluctuating velocities with a frequency above a certain fixed threshold, employed in the Large Eddy Simulation (LES), causes the appearance of a turbulent stress tensor that requires a number of closure assumptions. In this paper insufficiencies are demonstrated for those closure models which are based on a scalar eddy viscosity coefficient. A new model, based on a tensorial eddy viscosity, is therefore proposed; it employs the Germano identity [1] and allows dynamical evaluation of the single required input coefficient. The tensorial expression for the eddy viscosity is deduced by removing the widely used scalar assumption of the …

Direct Numerical Simulation of Pulsatile Turbulent Channel Flow

2008

Simulation of laser generated ultrasound with application to defect detection

2008

Laser generated ultrasound holds substantial promise for use as a tool for defect detection in remote inspection thanks to its ability to produce frequencies in the MHz range, enabling fine spatial resolution of defects. Despite the potential impact of laser generated ultrasound in many areas of science and industry, robust tools for studying the phenomenon are lacking and thus limit the design and optimization of non-destructive testing and evaluation techniques. The laser generated ultrasound propagation in complex structures is an intricate phenomenon and is extremely hard to analyze. Only simple geometries can be studied analytically. Numerical techniques found in the literature have pr…

Modelling and simulation of gas-liquid hydrodynamics in mechnically stirred tanks

2007

Abstract Computational fuid dynamics (CFD) is an increasingly important tool for carrying out realistic simulations of process equipment. In the case of multiphase systems the development of CFD models is less advanced than for single-phase systems. In the present work CFD simulations of gas–liquid stirred tanks are reported. An Eulerian–Eulerian multi-fluid approach is used in conjunction with the simplest two-phase extension of the k–ɛ turbulence model. All bubbles are assumed to share the same size. The effect of inter-phase forces on simulation results is separately considered. As concerns drag, it is shown that the sole parameter needed to characterize the dispersed phase behaviour is …

Prise en eau par composites carbone/époxy et leur effet sur le comportement mécanique : application aux réparations de structures en composite par co…

2013

Le travail présenté dans ce mémoire avait pour objectif d’étudier le processus de la pénétration d'eau dans les composites en carbone/époxyde dans un premier temps, et dans un deuxième temps, d’étudier l’effet de la prise en eau par ces matériaux sur les performances mécaniques des composites et leur joints collés. L'intégration de ces phénomènes physiques dans la modélisation numérique est d'une grande importance dans la prédiction de la durabilité d’une structure en composite subissant un vieillissement hygrothermique. Par conséquent, ce travail consiste non seulement en des observations expérimentales, mais aussi en des simulations numériques. Des corrélations entre les résultats obtenus…

Interactions and structures in polydisperse suspensions of charged spherical colloids

2018

Colloidal suspensions are found a bit everywhere around us, in construction materials,in cosmetics, in food, in biology. They are composed of nanometric or micrometric particlesdispersed in a gas, a liquid or sometimes a solid.This thesis is about colloidal suspensions in ionic solutions, where colloids bear anelectric charge, for example silica particles in an aqueous solution of sodium chloride,at a basic pH. The colloids, here approximated by spheres, can vary significantly in size,which can have an important effect on the behavior of these systems.This study aims at improving the understanding of these charged colloidal suspensionsby theoretical models solved by numerical simulations.of…

Expansion dynamics of the plasma plume formed by the impact of a nanosecond Nd : YAG laser beam on metallic surface under atmospheric conditions : ex…

2010

Laser ablation in the air at atmospheric pressure is nowadays frequently applied in industry, chemical analysis, surgery… For a further development of laser ablation based technologies, it is necessary to better understand the laser – matter interaction. During the impact of a laser pulse on the surface of the treated material, a plasma plume forms above the target surface. This plume contains particles (electrons, ions, atoms) of ablated matter, as well as of ambient gas, if present. During the laser pulse, this plume absorbs a large amount of the laser beam energy, thus reducing the quantity of the laser radiation arriving to the target surface. Dimensions, as well as parameters of this p…

Optimal valves regulation for calibration of pipe networks models

1998

The calibration of a pipe network model is faced by means of a two-steps iterative procedure. The first step of the procedure is the estimation of the parameters in the network simulation model, obtained from a first set of water head measures. The second step of the procedure is the change of the resistances provided by the valves in the network and the acquisition of a new set of measures. The inverse problem is then solved again and the procedure is repeated, until the set of computed parameters converge to stable values. The new resistances are chosen to minimize the sum of the variation coefficients, computed from the Fisher information matrix. The effect of different correlation funct…

Numerical Simulation of the Kinetics of Radical Decay in Single-Pulse High-Energy Electron-Irradiated Polymer Aqueous Solutions

2019

A new method for the numerical simulation of the radiation chemistry of aqueous polymer solutions is introduced. The method makes use of a deterministic approach combining the conventional homogeneous radiation chemistry of water with the chemistry of polymer radicals and other macromolecular species. The method is applied on single-pulse irradiations of aqueous polymer solutions. The speciation of macromolecular species accounts for the variations in the number of alkyl radicals per chain, molecular weight, and number of internal loops (as a consequence of an intramolecular radical-radical combination). In the simulations, the initial polymer molecular weight, polymer concentration, and do…