Pierre Joyot

On the use of model order reduction for simulating automated fibre placement processes

Automated fibre placement (AFP) is an incipient manufacturing process for composite structures. Despite its conceptual simplicity it involves many complexities related to the necessity of melting the thermoplastic at the interface tape-substrate, ensuring the consolidation that needs the diffusion of molecules and control the residual stresses installation responsible of the residual deformations of the formed parts. The optimisation of the process and the determination of the process window requires a plethora of simulations because there are many parameters involved in the characterization of the material and the process. The exploration of the design space cannot be envisaged by using standard simulation techniques. In this paper we propose the off-line calculation of rich parametric solutions that can be then explored on-line in real time in order to perform inverse analysis, process optimisation or on-line simulation-based control. In particular, in the present work, and in continuity with our former works, we consider two main extra-parameters, the first related to the line acceleration and the second to the number of plies laid-up.

Enriched reproducing kernel particle approximation for simulating problems involving moving interfaces

In this paper we propose a new approximation technique within the context of meshless methods able to reproduce functions with discontinuous derivatives. This approach involves some concepts of the reproducing kernel particle method (RKPM), which have been extended in order to reproduce functions with discon-tinuous derivatives. This strategy will be referred as Enriched Reproducing Kernel Particle Approximation (E-RKPA). The accuracy of the proposed technique will be compared with standard RKP approximations (which only reproduces polynomials).

Accounting for Incompressibility in Reproducing Kernel Particles Meshless Approximations

Meshless approximations seem to be an appealing choice for simulating forming processes involving large transformations because they allows alleviating the mesh constraints. However, because the novelty of these techniques a lot of questions are today unresolved. One of these open problems is the treatment of incompressibility which as well known impose some restrictions on the choice of the approximation spaces. The accurate treatment of incompressibility is a key point in the simulation of forming processes because the plastic flow can be in fact considered as incompressible. This paper introduces the problematic as well as some possibilities for taking into account the incompressibility in the context of mixed formulations, making special emphasis in a kind of Hermite approximations.

PGD-BEM Applied to the Nonlinear Heat Equation

The Boundary Element Method (BEM) allows efficient solution of partial differential equations whose kernel functions are known. The heat equation is one of these candidates when the thermal parameters are assumed constant (linear model). When the model involves large physical domains and time simulation intervals the amount of information that must be stored increases significantly. This drawback can be circumvented by using advanced strategies, as for example the multi-poles technique. We propose radically different approach that leads to a separated solution of the space and time problems within a non-incremental integration strategy. The technique is based on the use of a space-time separated representation of the unknown field that, introduced in the residual weighting formulation, allows to define a separated solution of the resulting weak form. The spatial step can be then treated by invoking the standard BEM for solving the resulting steady state problem defined in the physical space. Then, the time problem that results in an ordinary first order differential equation is solved using any standard appropriate integration technique (e.g. backward finite differences). When considering the nonlinear heat equation, the BEM cannot be easily applied because its Green’s kernel is generally not known but the use of the PGD presents the advantage of rewriting the problem in such a way that the kernel is now clearly known. Indeed, the system obtained by the PGD is composed of a Poisson equation in space coupled with an ODE in time so that the use of the BEM for solving the spatial part of the problem is efficient. During the solving, we must however separate the nonlinear term into a space-time representation that can limit the method in terms of CPU time and storage, that is why we introduce in the second part of the paper a new approach combining the PGD and the Asymptotic Numerical Method (ANM) in order to efficiently treat the nonlinearity.Copyright

Proper Generalized Decomposition - Boundary Element Method applied to the Heat Equation

In this paper, we propose a novel alternative of efficient non-incremental solution strategy for the heat equation. The proposed technique combines the use of the BEM with a Proper Generalized Decomposition (PGD) that allows a space-time separated representation of the unknown field within a non-incremental integration scheme.

New Advances in Meshless Methods: Coupling Natural Element and Moving Least Squares Techniques

We explore in this work the connections between NN and MLS approximations, coming from the introduction of the NN approximation functions as the weights in the scope of MLS. Thus, it is easy to adjust the approximation consistency (with the possibility to enrich the approximation basis with some particular functions describing issues of the searched solution) in the framework of the MLS techniques, precribing exactly essential boundary conditions from the use of the NN approximation as MLS weight. This approach opens, as will be proved in the present paper, the way to a wide range of formulations: (i) NN collocation strategies; (ii) faster natural element discretizations; (iii) Hermite natural element formulations; (iv) hierarchical bubbles functions in the natural element method; and (v) and NN enriched approximations.

Accounting for weak discontinuities and moving boundaries in the context of the Natural Element Method and model reduction techniques

Several thermomechanical models are defined in evolving domains involving fixed and evolving discontinuities. The accurate representation of moving boundaries and interfaces is, despite the significant progresses achieved in the recent years, an active research domain. This work focusses on the application of meshless methods for discretizing this kind of models, and in particular the ones based on the use of natural neighbor interpolations. The questions related to the description of moving boundaries, evolving weak discontinuities and the possibility of an eventual model reduction to alleviate the computational simulation cost, will be some of the topics here analyzed.