Multivalent cyclodextrin receptors in solution and at surfaces

This thesis deals with multivalent ß-cyclodextrin (CD) host-guest interactions in solution and at interfaces

Coherent thermodynamical modelling of geomaterial reinforced by wires

The TexSol is a composite geomaterial : a sand matrix and a wire network reinforcement. For small strains a thermodynamical continuous model of the TexSol including the unilaterality of the wire network is postulated. This model is described by two potentials which depend on some internal variables and a state variable either strain or stress tensor (the choice of this last one gives two different ways of identification). The TexSol continuous model is implemented in a finite element code to recover the mechanical behaviour given by discrete elements numerical experiments

On inconsistency in frictional granular systems

International audienceNumerical simulation of granular systems is often based on a discrete element method. The nonsmooth contact dynamics approach can be used to solve a broad range of granular problems, especially involving rigid bodies. However, difficulties could be encountered and hamper successful completion of some simulations. The slow convergence of the nonsmooth solver may sometimes be attributed to an ill-conditioned system, but the convergence may also fail. The prime aim of the present study was to identify situations that hamper the consistency of the mathematical problem to solve. Some simple granular systems were investigated in detail while reviewing and applying the related theoretical results. A practical alternative is briefly analyzed and tested

Conjugate gradient type algorithms for frictional multi-contact problems: applications to granular materials

International audienceThis paper presents gradient type algorithms to solve frictional multi contact problems written as quasi optimization problems. A single loop scheme formally close to the classical conjugate gradient method is proposed with some adap tations of the iterate corrections and gradient projections. Since the convergence is difficult to prove, various tests in the field of granular media are performed with comparison with the non linear Gauss Seidel scheme

From discrete to continuous numerical identification of a geomaterial with an internal length

International audienceA geomaterial called TexSol and composed of sand and wires was investigated by numerical experiments in order to determine its geometrical and mechanical parameters, such as tortuousness of the wire, anisotropy and characteristic length. This stage is essential for studying a material with an obvious non-local behavior. Investigations by discrete elements highlighted that the characteristic length was dependant on the loading level. These simulations provided access to variables that standard physical experiments cannot provide. Some parameters of a continuous model of TexSol were identified through discrete numerical experiments using a classic procedure. The other parameters were determined by finite element method updating

A parallel version of the non smooth contact dynamics algorithm applied to the simulation of granular media

AbstractThe NSCD method has shown its efficiency in the simulation of granular media. Since the number of particles and contact increases, the shape of the discrete elements becomes more complicated and the simulated problems becomes more complex, the numerical tools need to be improved in order to preserve reasonable elapsed CPU time. In this paper we present a parallelization approach of the NSCD algorithm and we investigate its influence on the numerical behaviour of the method. We illustrate the efficiency on an example made of hard disks: a free surface compaction

Numerical investigations of fault propagation and forced-fold using a non smooth discrete element method

Geophysical problems as forced-fold evolution and fault propagation induce large deformations and many localisation. The continuum mechanics does not seem the more appropriate for their description and it appears more interesting to represent the media as initially discontinuous. To face both phenomena, a non smooth Discrete Element Method is used. Geophysical structures are considered as collection of rigid disks which interact by cohesive frictional contact laws. Numerical geophysical formations are correlated to mechanical properties of structures through observation and mechanical analysis.Les problèmes géophysiques tels que l’évolution des plis et la propagation de failles induisent de grandes déformations et de nombreuses localisations. Il apparaît donc difficile de décrire le problème avec les outils de la mécanique des milieux continus, et il est donc preferable de représenter la structure comme initialement divisée. Ces deux phénomènes sont étudiés via une approche non régulière par éléments discrets. Les structures géologiques sont considérées comme des collections de particules dont les interactions répondent à des lois de contact cohésif frottant. Les observations des structures géophysiques numériques sont corrélées aux propriétés des structures au travers d’une analyse mécanique

A domain decomposition strategy for nonclassical frictional multi-contact problems

International audienceIn this paper we present a numerical strategy to be solve large scale frictional contact problems by domain decomposition methods which are adapted to parallel computers. The motivation is given by the study of the mechanical behavior of rolling shutters composed by many hinged slats. The numerical treatment of such nonclassical contact problems leads to very large strongly nonlinear, nonsymmetric and ill-conditioned systems. Domain decomposition methods are a good alternative to overcome the difficulties of classical sequential solutions. We present a nonlinear strategy adapted to problems, called “multi-contact” problems

Prediction of wrinkling and springback in sheet metal forming

The finite element simulation is currently a powerful tool to optimize forming processes in order to produce defect-free products. Wrinkling and springback are main geometrical defects arising in sheet metal forming. Nevertheless, the prediction of such defects requires accurate numerical models. This study presents the experimental and numerical analysis of a rail with high tendency to develop both wrinkling (top surface of geometry) and springback (flange). The punch force evolution and the final geometry of the rail, evaluated in four different cross-sections, are the main variables analysed. Globally, the numerical results are in good agreement with the experimental measurements. However, the shape of the wrinkle is significantly influenced by the symmetry conditions considered in the model (1/4 of the blank). In fact, considering the full model of the blank, the numerical results are in better agreement with the experimental ones. On the other hand, the computational cost of the numerical simulation considering the full blank is approximately 12 times higher than using 1/4 of the blank.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under projects with reference UID/EMS/00285/2013, PTDC/EMS-TEC/0702/2014 (POCI-01-0145-FEDER-016779) and PTDC/EMS-TEC/6400/2014 (POCI-01-0145-FEDER-016876) by UE/FEDER through the program COMPETE2020. The first author is also grateful to the FCT for the Postdoctoral grant SFRH/BPD/101334/2014