Exploring the Strategic Benefits of 0V Storage for Na-ion Batteries
Recently deployed on a commercial scale, the Na-ion battery technology demonstrates excellent behaviour during medium or long-term storage at zero voltage. This characteristic offers numerous safety advantages during the transport, assembly and storage of cells and modules, as well as during emergency shutdowns in the event of external issues. But are there no consequences for battery performance?
This research project aims to study and better understand the electrochemical mechanisms at play when the potential difference across the terminals is maintained at 0 V.
Initially, advanced dynamic characterisation techniques will be used to analyse and compare the electrochemical, thermal and mechanical properties of battery materials. The results will enrich calendar and cycling ageing models at the cell scale, thereby improving their accuracy and reliability. Subsequently, tests will be conducted on mini-battery modules assembled in various electrical architectures to study cell behaviour during cycling and ageing, particularly in response to the application of negative voltage. Specific battery management system (BMS) solutions could then be proposed to address these issues.
The scientific approach will involve implementing advanced characterisation and instrumentation techniques, conducting ageing and safety tests to identify mechanisms, and developing ageing models. This approach will draw on the expertise and testing facilities of CEA-Liten at the Bourget du Lac site in Savoie.
Hybrid CPU-GPU Preconditioning Strategies for Exascale Finite Element Simulations
Exascale supercomputers are based on heterogeneous architectures that combine CPUs and GPUs, making it necessary to redesign numerical algorithms to fully exploit all available resources. In large-scale finite element simulations, the solution of linear systems using iterative solvers and algebraic multigrid (AMG) preconditioners remains a major performance bottleneck.
The objective of this PhD is to study and develop hybrid preconditioning strategies adapted to such heterogeneous systems. The work will investigate how multilevel and AMG techniques can be structured to efficiently use both CPUs and GPUs, without restricting computations to a single type of processor. Particular attention will be paid to data distribution, task placement, and CPU–GPU interactions within multilevel solvers.
From a numerical point of view, the research will focus on the analysis and construction of multilevel operators, including grid hierarchies, intergrid transfer operators, and smoothing procedures on avalible GPU's and CPU's. The impact of these choices on convergence, spectral properties, and robustness of preconditioned iterative methods will be studied. Mathematical criteria guiding the design of efficient hybrid preconditioners will be investigated and validated on representative finite element problems, e.g., regional-scale earthquake analysis.
These developments will be coupled with domain decomposition and parallelization strategies adapted to heterogeneous architectures. Particular attention will be paid to CPU–GPU data transfers, memory usage, and the balance between compute-bound and memory-bound kernels. The interaction between numerical choices and hardware constraints, such as CPU and GPU memory hierarchies, will be designed and developed to ensure scalable and efficient implementations.
A macroscale approach to evaluate the long-term degradation of concrete structures under irradiation
In nuclear power plants, the concrete biological shield (CBS) is designed to be very close of the reactor vessel. It is expected to absorb radiation and acts as a load-bearing structure. It is thus exposed during the lifetime of the plant to high level of radiations that can have consequences on the long term. These radiations may result especially in a decrease of the material and structural mechanical properties. Given its key role, it is thus necessary to develop tools and models, to predict the behaviors of such structures at the macroscopic scale.
Based on the results obtained at a lower scale - mesoscopic simulations, from which a better understanding of the irradiation effect can be achieved and experimental results which are expected to feed the simulation (material properties especially), it is thus proposed to develop a macroscopic methodology to be applied to the concrete biological shield. This approach will include different phenomena, among which radiation-induced volumetric expansion, induced creep, thermal defromations and Mechanical loading.
These physical phenomena will be developed within the frame of continuum damage mechanics to evaluate the mechanical degradation at the macroscopic scale in terms of displacements and damage especially. The main challenges of the numerical developments will be the proposition of adapted evolution laws, and particularly the coupling between microstructural damage and damage at the structural level due to the stresses applied on the structure.
Li alloys for all solid-state batteries with sulfide electrolyte
Using lithium metal as a negative electrode would significantly increase the energy density of current batteries. However, today, this material quickly leads to short circuits during charge/discharge cycles, mainly due to the formation of dendrites and the instability of the interface with the electrolyte. All-solid-state batteries, particularly with sulfide electrolytes, are a promising alternative, but the limitations of lithium metal remain. Lithium alloys appear to be a solution for improving mechanical and interfacial properties while maintaining good energy densities.
The objective of the PhD is to develop and select lithium alloys suitable for sulfide electrolytes batteries, then integrate them into all-solid-state cells in order to study degradation mechanisms. The work will be focused on the synthesis of the alloys, their shaping in thin films and their integration into cells. The alloys will be finely characterized and then electrochemically tested in laboratory cells and pouch cells. Finally, degradation phenomena, particularly at interfaces, will be studied using advanced post-mortem characterizations.
Development of a new numerical scheme, based on T-coercivity, for discretizing the Navier-Stokes equations.
In the TrioCFD code, the discretization of the Navier-Stokes equations leads to a three-step algorithm (see Chorin'67, Temam'68): velocity prediction, pressure solution, velocity correction. If an implicit time discretization scheme is to be used, the pressure solution step is particularly costly. Thus, most simulations are performed using an explicit time scheme, for which the time step depends on the mesh size, which can be very restrictive. We would like to develop an implicit time discretization scheme using a stabilized formulation of the Navier-Stokes problem based on explicit T-coercivity (see Ciarlet-Jamelot'25). It would then be possible to solve an implicit scheme directly without a correction step, which could significantly improve the performance of the calculations. This would also allow the use of the P1-P0 finite element pair, which is frugal in terms of degrees of freedom but unstable for a classical formulation.
Development of a modeling tool for corrosion in porous media
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In a context where material durability is essential for the safety of infrastructures and the promotion of a sustainable energy transition, mastering corrosion phenomena represents a major challenge for key sectors such as decarbonized energy transport through buried pipelines and civil engineering (hydrogen, nuclear, underground infrastructures). The CORPORE project addresses this issue by proposing the development of advanced numerical simulation models to study corrosion in porous media using COMSOL Multiphysics.
The main scientific and technological objective is to establish an integrated multiphysics modeling approach for the electrochemical and transport mechanisms within porous materials: studying the coupled influence of chemistry, pore network properties, and material–environment interactions on the initiation and propagation of corrosion.
This approach will help optimize anticorrosion protection strategies, reduce maintenance costs, and extend the service life of structures. From a state-of-the-art perspective, most current models focus on homogeneous media and compartmentalized approaches. Our project stands out by integrating a multi-scale mechanistic modeling framework combined with the use of archaeological data for long-term validation.
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Investigation of polytopal methods apllied to CFD and optimized on GPU architecture
This research proposal focuses on the study and implementation of polytopal methods for solving the equations of fluid mechanics. These methods aim to handle the most general meshes possible, overcoming geometric constraints or those inherited from CAD operations such as extrusions or assemblies that introduce non-conformities. This work also falls within the scope of high-performance computing, addressing the increase in computational resources and, in particular, the development of massively parallel computing on GPUs.
The objective of this thesis is to build upon existing polytopal methods already implemented in the TRUST software, specifically the Compatible Discrete Operator (CDO) and Discontinuous Galerkin (DG) methods. The study will be extended to include convection operators and will investigate other methods from the literature, such as Hybrid High Order (HHO), Hybridizable Discontinuous Galerkin (HDG), and Virtual Element Method (VEM).
The main goals are to evaluate:
1. The numerical behavior of these different methods on the Stokes/Navier-Stokes equations;
2. The adaptability of these methods to heterogeneous architectures such as GPUs.
Robust multi-material topological optimization under manufacturability constraints applied to the design of superconducting magnets for high-field MRI
MRI scanners are invaluable tools for medicine and research, whose operation is based on exploiting the properties of atomic nuclei immersed in a very intense static magnetic field. In almost all MRI scanners, this field is generated by a superconducting electromagnet.
The design of electromagnets for MRI must meet very demanding requirements in terms of the homogeneity of the field produced. In addition, as the magnetic field becomes more intense, the forces exerted on the electromagnet increase, raising the issue of the mechanical strength of the windings. Finally, the “manufacturability” of the electromagnet imposes constraints on the shapes of acceptable solutions. The design of superconducting electromagnets for MRI therefore requires a meticulous effort to optimize the design, subject to constraints based on magneto-mechanical multiphysics modeling.
A new innovative multiphysics topological optimization methodology has been developed, based on a density method (SIMP) and a finite element code. This has made it possible to produce magnet designs that meet the constraints on the homogeneity of the magnetic field produced and on the mechanical strength of the windings. However, the solutions obtained are not feasible in practice, both in terms of the manufacturability of the coils (cable windings) and their integration with a supporting structure (coils held in place by a steel structure).
The objective of this thesis is to enhance the topological optimization method by formalizing and implementing manufacturing constraints related to the winding method, residual stresses resulting from pre-tensioning the cables during winding, and the presence of a structural material capable of absorbing the forces transmitted by the coils.
development of a NET (Negative Emission Technologie) process combining CO2 capture and hydrogenation into synthetic fuel
Until recently, CO2 capture technologies were developed separately from CO2 utilization technologies, even though coupling the CO2 desorption stage with the chemical transformation of CO2, which is generally exothermic, would yield significant energy savings.
The first coupled solutions have recently been proposed, but they are mainly at moderate temperatures (100-180°C) [1], or even recently close to 225°C [2].
The objective of this doctoral thesis is to study, both experimentally and theoretically, a coupled system in the 250-325°C temperature range that allows via Fischer-Tropsch-type catalytic hydrogenation the direct production of higher value-added products