Alain Combescure

A numerical scheme to couple subdomains with different time-steps for predominantly linear transient analysis

Abstract This paper generalizes the explicit/implicit time-integration algorithms pioneered by Belytschko, Hughes and their respective co-workers, and the FETI domain decomposition methods introduced by Farhat and his co-workers, to the case where the same Newmark scheme, but different β and γ coefficients and different time-steps, are specified in each subdomain. Building upon the work of Farhat, Crivelli and Geradin, it considers various interface boundary constraints and performs a stability analysis of the proposed time integration algorithms.

The influence of circumferential thickness variations on the buckling of cylindrical shells under external pressure

Abstract Imperfection sensitivity of thin shells of constant thickness was widely studied during the last 50 years (J.G. Teng, Appl. Mech. Rev. 1996:49(4)). Recently, Koiter et al. (Int. J. Solids Struct. 1994:31(6):797–805) investigated the influence of axisymmetric modal thickness variation on the buckling load of an axially compressed shell. In this paper, the influence of harmonic thickness variation in the circumferential direction on thin cylindrical shell buckling under external pressure is analysed by means of FE bifurcation analysis. Two different FE codes were used, one with quasi-axisymmetrical multimodal Fourier analysis (A. Combescure, Etude de la stabilite des coques minces sous chargements complexes dans INCA. Rapport DMT/94-460, in French, 1994; Modelisation des coques axisymetriques avec imperfection quelconque: L’element COMI (in French). Rapport DMT/97-189, 1997; Schauder B. Flambage des Coques Cylindriques en Flexion. These de doctorat, INSA de Lyon, in French, 1997), and the second one with 3D shell elements. A new quasi-axisymmetric element (COMI) is presented. It uses Fourier series expansion in the circumferential direction coupled with a full numerical integration around the circumference, which allows any variation of thickness or of initial imperfections.

Traitement d'impact fluide-solide par la méthode particulaire SPH: Application: ingestion d'oiseau par les turboréacteurs

ABSTRACT A SPH method has been developed for the simulation of soft impacts of a fluid on a structure. The SPH method is coupled to a finite element method using a slave-master contact impact algorithm. An implementation has been performed in the Castem-Plexus explicit code. It is applied to bird swalling simulation in a turboreactor engine. The final strains and deformed shapes of the turbine blades are correctly predicted and the computation times are reasonable enough to do industrial applications.