Une technique sans maillage pour simuler l'écoulement d'un fuide compressible à surface libre

Dans cette communication, nous présentons une méthode sans maillage couplée avec une technique implicite d'ordre élevé pour la simulation des écoulements de fuides compressibles. Les dificultés de la mise en oeuvre numérique sont axées sur les équations du mouvement et les conditions aux limites. Cet algorithme combine les procédures mathématiques suivantes: une discrétisation en temps, une méthode des moindres carrés mobiles MLS, une transformation d'homotopie, un développement en séries de Taylor et d'une méthode de continuation [1, 2, 3]. L'algorithme proposé permet d'obtenir un grand nombre de pas de temps qui minimise le nombre de décompositions de matrices tangentes. La formulation forte est considérée pour éviter l'inconvénient d'intégration numérique. Les conditions aux limites de la surface libre sont traitées par la technique de collocation qui est la plus appropriée pour les grandes déformations sans la nécessité de redénir le maillage

Numerical model based on meshless method to simulate FSW

In the present work, a numerical models based on the meshless method “the smoothed particle hydrodynamics (SPH)” is developed to simulate the Friction Stir Welding (FSW). This technique type is well adapted to modeling of mixing zone which is subjected to high strain rate. We limit ourselves to two dimensional problems

A 2D Fourier double scale analysis of global-local instability interaction in sandwich structures

In sandwich structures, with a soft core and stiff skins, under in-plane compressive loading, global buckling of the whole structure and local wrinkling on the skin can occur. Several works have been developed to investigate the buckling and post-buckling behavior of sandwich structures (Léotoing, Drapier and Vautrin, IJSS, EJM-A 2002). The bifurcation analysis according to the Landau–Ginzburg equation can be used to study these instabilities, which follows from an asymptotic double scale analysis. This bifurcation equation is valid only close to the critical state and it is not able to account for the coupling between a global non-linear behavior and the appearance of wrinkles. A new approach has been presented by Damil and Potier-Ferry (EJCM 2008, JMPS 2010) that is based on the concept of Fourier series with slowly varying coefficients. The obtained models are consistent with the Landau–Ginzburg theory, but they may also remain valid away from the bifurcation point and the coupling between global and local instabilities can be accounted for. In this work, we present a new Fourier double scale analysis to study the interaction of local wrinkling and global buckling of 2D sandwich structures. By this way, a 2D microscopical sandwich model is transformed into 2D macroscopical one and only the envelopes of instability patterns are numerically evaluated. This new non-linear macroscopic 2D model of sandwich structures is then solved by the Asymptotic Numerical Method (Cochelin, Damil and Potier-Ferry, IJNME 1994). The proposed 2D Fourier double scale model of sandwich structures is validated by comparison with the 1D Fourier double scale model of sandwich structures of Liu, Yu, Hu, Belouettar, Potier-Ferry and Damil, IJSS 2012 and the 2D microscopical model. Accurate results have been obtained

Changing Cause of Death Profile in Morocco: The Impact of Child-survival Programmes

This study was carried out to evaluate the trends in cause-specific mortality and the impact of child-survival programmes in Morocco. Two national surveys on causes and circumstances of child deaths were conducted in Morocco in 1988 and 1998 (ECCD-1 and ECCD-2 respectively). These surveys were based on a representative sample of deaths of children aged less than five years (432 and 866 re\uadspectively). Causes of death were assessed by verbal autopsy and were validated on a subsample of 94 cases. Data on causes of deaths were matched with death rates from demographic surveys (Enqu\ueate Nationale D\ue9mographique \ue0 Passages R\ue9p\ue9t\ue9s and Demographic and Health Survey) to compute cause-specific death rates. Morocco underwent a dramatic mortality decline since independence, and the decline in mortality among children aged less than five years was particularly rapid over the 1988-1997 period, at an average rate of -6% a year, and faster for children (aged 1-4 year(s)) than for infants. The decline in mortality varied markedly by causes of death and was most pronounced for causes due to vaccine-preventable diseases, such as neonatal tetanus, measles, whooping cough, tuberculosis, for diarrhoeal diseases and malnutrition, and for selected infectious diseases. However, mortality due to acute lower respiratory infection (ALRI) outside the neonatal period did not change significantly as was the case for some neonatal conditions (birth trauma and prematurity) and for accidents. The decline in cause-specific mortality could be attributed to the success of public-health programmes: the Expanded Programme on Immunization, the management of diarrhoeal diseases and malnutrition, and the use of antibiotics for selected infectious diseases. It is likely that improve\uadments in living conditions, child-feeding practices, hygiene, and sanitation also contributed to the decline in mortality, although these could not explain the magnitude of the changes for target diseases. In contrast, the ALRI programme, which started after 1997, could not have any effect yet, and conditions of delivery and care of the newborn improved only marginally over the study period

Une approche thermomécanique 2D pour la simulation du procédé FSW

L'objectif de notre travail est la modélisation thermomécanique du malaxage d'un matériau viscoplastique observé lors du procédé de soudage par friction et malaxage FSW. Nous proposons un algorithme basé sur le couplage d'une approche sans maillage et une technique implicite d'ordre élevé. Une comparaison des résultats est eectuée dans le cas bidimensionnel avec une approche itérative