Aspects thermomecaniques de la modelisation par elements finis du prechauffage electrique d'une cuve de Hall-Heroult: Lois constitutives, conception orientee-objet et validation (French text).

摘要

The study of the aluminium extraction from its oxyde is a vast and challenging field. The industrial Hall-Heroult process involves complex interactions between thermal, electrical, mechanical, magnetics and fluid mechanics phenomena within the cells. Accordingly, their start-up is a delicate procedure. This thesis was conducted within the context of the START-CUVE project, aiming at simulating the thermal, electrical and mechanical phenomena taking place during the electrical preheating of a cell---the first stage of the start-up. The underlying goal is to improve the cell life and performance.; Specifically, this thesis deals with the thermomechanical aspects of non carbonaceous materials. Hence, an adequate constitutive law will be proposed or adapted for different materials; for refractory concrete, a thermo-chemo-mechanical law will even be developped from principles of thermodynamics of irreversible processes and mechanics of reactive porous continua. Numerical simulation results will systematically be compared to experimental data in order to assess the validity of the proposed laws.; A chapter will be entirely devoted to the discretisation and the linearisation of the variational forms for the thermochemical and mechanical problems. The constitutive laws numerical integration algorithms and consistent tangent operators will be derived in the appendices.; The coupled-field nature of the problem, with several different material behaviours, several different parameter sets as well as couplings between phenomena through internal variables, makes it difficult to solve using traditional procedural softwares. Therefore, original Object-Oriented libraries were developped in the in-house finite element toolbox FESh++ to manage internal variables, materials and constitutive laws. Stricking examples will be presented as to how these new flexible structures quickly make possible the construction of complex material behaviour models.; Finally, a thermo-chemo-mechanical small scale set-up, nevertheless representative of the cell condition during preheating, will be analysed in the transient regime for validation purposes.