Frictionless contact problem for hyperelastic materials with interior point optimizer

This paper presents a method to solve the mechanical problems undergoing finite deformations and the unilateral contact problems without friction for hyperelastic materials. We apply it to an industrial application: contact between a mechanical gasket and an obstacle. The main idea is to formulate the contact problem into an optimization's one, in order to use the Interior Point OPTimizer (IPOPT) to solve it. Finally, the FreeFEM software is used to compute and solve the contact problem. Our method is validated against several benchmarks and used on an industrial application example

Contact Problems in Industrial Applications Using FreeFEM

This paper presents an algorithm and a method to solve mechanical contact problems between two bodies or more, for linear elastic and finite deformation problems. The contact problem is considered as an optimization one, more specifically as a minimization problem. The interior point method is used to solve the minimization problem. This algorithm is symmetric and the user does not need to specify anymore a slave and a master body. The algorithm was developed using FreeFEM and IPOPT software

Frictionless contact problem for hyperelastic materials with interior point optimizer

This paper presents a method to solve the mechanical problems undergoing finite deformations and the unilateral contact problems without friction for hyperelastic materials. We apply it to an industrial application: contact between a mechanical gasket and an obstacle. The main idea is to formulate the contact problem into an optimization's one, in order to use the Interior Point OPTimizer (IPOPT) to solve it. Finally, the FreeFEM software is used to compute and solve the contact problem. Our method is validated against several benchmarks and used on an industrial application example

e-Pilly TROP Maladies infectieuses tropicales

L’e-Pilly TROP est un ouvrage d’infectiologie tropicale destiné aux médecins et aux étudiants en médecine des pays francophones du Sud. La prise en compte des différents niveaux de la pyramide sanitaire dans ces pays le rend aussi accessible aux infirmiers des centres de santé communautaires urbains et des structures de santé intermédiaires des zones rurales. Par définition, les Pays En Développement accroissant progressivement leurs capacités de diagnostic biologique et de traitement, les outils de prise en charge correspondent aux moyens des niveaux périphériques comme à ceux des niveaux hospitaliers de référence

Modélisation numérique de la pression intracrânienne via les écoulements du liquide cérébrospinal et du sang mesurés par IRM de flux

La modélisation de la pression intracrânienne est un sujet de thèse pluridisciplinaire faisant intervenir aussi bien des connaissances en mathématiques appliquées, utiles pour résoudre les équations de la mécanique des fluides et des interactions fluide-structure, qu'en anatomie ou en physiologie, afin de modéliser correctement le système cérébrospinal. L'objectif de ce travail est de déterminer de manière non invasive la pression intracrânienne. Différentes méthodes numériques, utilisant la méthode des éléments finis, sont présentées puis validées avant d'être appliquées à nos modèles numériques. Le premier modèle, faisant intervenir uniquement la composante fluide du système cérébrospinal, est une bifurcation prenant en compte les trois compartiments principaux de liquide cérébrospinal. Le second modèle, prenant maintenant en compte les structures présentes dans le système cérébrospinal, est une représentation simplifiée de ce système en interaction fluide-structure. Parallèlement à cette étude numérique, une étude sur des données expérimentales, de flux et de pression, est réalisée afin d'alimenter nos modèles numériques, de comparer nos résultats de simulation, et de mieux appréhender le comportement du système cérébrospinal in vivoIntracranial pressure modeling is a multidisciplinary PhD thesis subject involving both applied mathematics knowledge, useful to solve the fluid mechanics equations and fluid-structure interactions problems, and in anatomy or physiology, to correctly model the cerebrospinal system. The goal of this work is to determine non-invasively the intracranial pressure. Different numerical methods, using the finite element method, are presented and validated before being applied to our numerical models. The first model, involving fluid component of the cerebrospinal system only, is a bifurcation taking into account the three main cerebrospinal fluid compartments. The second model, now taking into account structure in the cerebrospinal system, is a simplified representation of this system in fluid-structure interaction. Along with the numerical study, a study on experimental data, flow and pressure, is conducted to serve our numerical models, to compare our simulation results, and to better understand the cerebrospinal system behavior in viv

Aliasing affects ActiLife software raw accelerometry to count conversion from different sampling frequencies

International audienceAccelerometry counts are widely used to quantify physical activity in an objective manner. ActiGraphTM accelerometers offer to record acceleration signal with different sampling frequency (fs). Nevertheless additional counts were shown to be computed by ActiLife software from acceleration signal with a sampling frequency fs>30 Hz compared to signal with default fs=30 Hz or multiple. This paper relies on the study of synthetic signals to point out the origin of this error and to recommend an adjusted method. A piecewise-frequency sinus time series (0-15 Hz) was generated at different sampling frequencies (fs=30, 50 and 100 Hz). The artificial acceleration raw signal was resampled to 30 Hz using different antialiasing lowpass filters before ActiLife count computation. The use of an antialiasing filter which did not properly attenuate aliasing replicas was found to induce aliasing frequencies within ActiLife bandpass filter which is the cause of extract activity counts. We were able to reproduce fictitious counts for acceleration around 10 Hz. A simple adjustment of antialiasing filter parameters allowed to avoid this problem. This study reproduces ActiLife counts processing from 50 and 100 Hz sampled signal. Count overestimations from fs=50 and 100 Hz signal were induced because of aliasing in the frequency bandwidth of the ActiLife count filter. This can be corrected by a relevant antialiasing filtering before ActiLife software processing or this can be done in high-level mathematical programing

Physical activity estimation from accelerometry

International audienceObjective physical activity (PA) quantification is traditionally achieved using lightweight accelerometers accounting for activity frequency, intensity and duration. The accelerometer data are usually converted into activity counts and these counts can be used on their own to quantify the intensity and duration of a PA period or they can serve as features for energy expenditure computation or activity classification. This paper investigates the way how Actigraph counts are computed. Several points are discussed regarding bandpass filtering and amplitude non-linearities that may hamper some analysis. Experimental data were used 1) to assess reconstructed filter performances to replicate ActiGraph counts during an urban-circuit involving 20 subjects wearing an ActiGraph GT3X+ and 2) explain filter limitations (e.g. plateauphenomenon) thanks to a treadmill test with incremental speed (n=4). This study reproduces well ActiLife filter and reveals the impact of band-pass filtering on ActiLife count conversion. These results provide some keys to interpret knowingly ActiLife count based studies

Frictionless contact problem for hyperelastic materials with interior point optimizer

This paper presents a method to solve the mechanical problems undergoing finite deformations and the unilateral contact problems without friction for hyperelastic materials. We apply it to an industrial application: contact between a mechanical gasket and an obstacle. The main idea is to formulate the contact problem into an optimization's one, in order to use the Interior Point OPTimizer (IPOPT) to solve it. Finally, the FreeFEM software is used to compute and solve the contact problem. Our method is validated against several benchmarks and used on an industrial application example

PHANTOM project: development and validation of the pipeline from MRA acquisition to MRA simulations

The aim of this project is to validate the Vivabrain pipeline with a physical phantom from real MRI acquisition to MRI simulations through image segmentation and computational fluid dynamics (CFD) simulations. For that purpose, we set up three comparison benchmarks. The first benchmark compares dimensions of the reconstructed geometry from real MRI acquisition to the physical phantom dimensions. The second aims to validate the CFD simulations by comparing the outputs of two simulations, one carried out using Feel++ and the other using FreeFem++. The CFD outputs are also compared to MRI flow measurement data. The goal of the last comparison benchmark is to compare the MRI simulations outputs to the numerical fluid simulations