Experimentation and numerical simulation of lithium battery thermal runaway
In the current Energy transition context, the lithium battery is an essential technology to address the strong challenge of the electrical energy storage. However, Li battery severe solicitations/loadings can lead to a thermal runaway phenomenon, which can cause an outbreak of fire, even an explosive combustion of the cell or of the whole battery pack. If this phenomenon is well known, the research and development dedicated to the battery safety is emerging and must be consolidated. The post-doctorate global objective is to develop a numerical modelling and simulation strategy for thermal runaway occurring when a Li battery is subjected to mechanical/thermal/electrical abuse, in order to gain an understanding of the phenomenon, estimate the thermal spreading risk as a result of gas combustion, or study the runaway mechanical consequences (fluid structure interaction). This strategy relies on physical testing campaigns carried out as part of the post-doctorate, and on numerical tools developed by CEA (EUROPLEXUS, Cast3M). The work will be organised into three main content areas: Understanding and modelling of the phenomena on the basis of experimental tests (shock tube, abusive tests), Development of a numerical model representative of identified phenomena, Modelling including fluid-structure interaction (case deformation due to pressure increase).
Wood modifications by supercritical CO2
In order to replace current high environmental impact construction materials, CEA leads research work on chemical functionalization of wood (from French local forests) to improve its properties and make them a viable substitute of these construction materials or imported construction wood.
In this frame, chemistry under supercritical CO2 appears to be an efficient way to carry innovative chemistries while liùmiting the environmental impact & VOCs emissions of such processes.
Thus, you will be in charge of the development of new processes of chemical modification of local wood species under supercritical CO2. You will lead the research project by perfroming the state of the art, making technical propositions (around the adapted functionalization chemistries), carrying out the eperiments & the characterizations and will be in charge of respecting the deadlines & redacting the associated deliverables.
Use and extension of the Alien solver library with the proto-application Helix
First, the post-doc candidate will have to integrate the solver Library Alien into Helix to carry out performance and usability assessments in iterative or direct solver configuration. These assessments will be done on different computer architecture from desktop computer to national supercomputer with thousands of cores.
In a second time, the candidate will deal with the possibility to add new functionalities in the Alien library to solve non-linear systems composed with equations and inequations to be able to solve, in an HPC context, mechanical problems like phase field problem or contact problems, problems often still opened in the community. The results will be compared to the classical test cases and benchmarks of the state of the art in the domain.
The candidate will join the Helix development team, formed by 3/4 developers for the moment in the laboratory LM2S (15 persons). A transversal program between CEA directions finances the post-doc and the candidate will collaborate with the Alien library developers at the DAM of CEA.
Development of flexible solar panel for space application
Traditional solar panels used to power satellites can be bulky with heavy panels folded together using mechanical hinges. Smaller and lighter than traditional solar panels, flexible solar array consists of a flexible material containing photovoltaic cells to convert light into electricity. Being flexible, the solar array could roll or snap using carbon fiber composite booms to deploy solar panels without the aid of motors, making it lighter and less expensive than current solar array designs.
On the other hand, satellite trends are shifting away from one-time stints and moving towards more regular use in a constellation setting. In the last years, the desire increased to mass-produce low-weight satellites. Photovoltaic arrays companies are challenged on their capacity to face these new needs in terms of production capacity and versatility. And this is exactly where space photovoltaics can learn from terrestrial photovoltaics where this mass production and low-cost shift occurred years ago.
To tackle these new challenges, the Liten institute started to work on these topics two years ago. In the frame of this post-doc, we propose the candidate to work on the development of an innovative flexible solar panel architecture, using high throughput assembly processes. We are looking for a candidate with a strong experience in polymers and polymers processing, along with an experience in mechanics. A previous experience in photovoltaic will be greatly appreciated.
Continuum models calibration strategy based on a 3D discrete approach
In order to develop an identification strategy for continuum constitutive models devoted to quasi-brittle materials, suited for structural analysis, often realized arbitrarily, a model based on the discrete element method has been formulated. The discrete model is used to compensate the lack of experimental data required to calibrate the continuum model. Thanks to intrinsic predispositions with respect to fracture mechanisms, the discrete model can be used easily, and its efficiency has been proved. However, only 2D simulations have been undertaken so far, mostly due to computational costs limitations.
A 2D framework reduces extensively analysis possibilites with such model, in particular for reinforced structures where 3D effects are predominant. The purpose of the present post-doctoral work is to extend to 3D the discrete approach already developped in 2D. The developments will be integrated in the FEA code CAST3M-CEA developped by DEN/DANS/DM2S/SEMT. In the mean time, the discrete model will be optimized using available tools, such as solvers, available in the CAST3M-CEA environment. Depending on the computational costs improvements, even complete structures simulations might be considered.
At the end of this work, the developed numerical tool will allow to extend the identification stragegy to constitutive models including 3D effects, such as steel/concrete interface models (confinement) and concrete model (dilatancy).
Nonlinear dynamic analysis of a reinforced concrete structure subjected to seismic loadings: Deterministic and probabilistic study of response spectra
The proposed work is based on the experimental campaign of the ENISTAT project and is composed of three parts:
1. Calibration and enhancement of the numerical model (5 months)
Based on the nonlinear numerical model that has been realized in CEA, the applicant will have to compare the results to those provided by the experimental campaign. The potential gaps will be interpreted and the model should be calibrated (and/or enhanced) to ensure a satisfactory accordance with the experimental results and observations.
2. Deterministic and probabilistic analysis of response spectra (5 months)
Based of the numerical model that will have been calibrated, the response spectra will be computed in given points. They will be compared the demand spectra prescribed by the design rules such as the EC8. Based on probabilistic methods that are developed in CEA for seismic applications, the uncertainties not only of the input parameters but also of the seismic signals will be taken into account. The induced variability of the response spectra will be quantified and discussed. One can notice that the knowledge of these data is particularly interesting since design rules in seismic engineering are based on them.
3. Study of the effect of the thermic brick elements
Thanks to the experimental results, not only experimental but also numerical, a discussion on the effect of the thermic brick elements will be realized with the aim to draw first conclusions on their effect on the overall structural behavior under seismic loading.
Modelling of actinide electrorefining
Modelling of an actinide electrorefining process
In the frame of the SACSESS European project CEA, ITU and CNRS are studying jointly a pyrochemical process for the reprocessing of spent nuclear fuels by electrolysis in molten chloride salts.
The main objective of the proposed post-doctoral work concerns the modelling of electrorefining runs onto aluminium cathodes using U-Pu-Zr-Am-Gd-Nd-Ce-Y metallic alloy. The modelling aims to evaluate the efficiency of this electrolytic process in terms of separation factors and to optimize the process flow sheets for a safe nuclear materials management.
Model reduction in dynamics : application to earthquake engineering problems
The complexity and refinement of the numerical models used to predict the behavior of structures under seismic loading often impose computation times of several days for solving the partial differential equations of the reference problem.
Furthermore, in the context of optimization , model identification, or parametric and stochastic analyses, the aim is not to predict the response of a unique model but of a family of models.
To reduce the computation time, model reduction techniques (Proper Orthogonal/Generalized Decomposition) may be considered. This post-doctoral study proposes to define and implement (especially in the FE code CAST3M) a technique suitable for the reduction of reinforced concrete type models subjected to seismic loading.
Study of aerosol transport through degraded materials
Radioactive Waste (RW) are produced during nuclear activities and are categorized as a function of their activities and their half-life in order to manage their conditioning, transport, storage… Mortar can be used in order to immobilize and/or create a safe barrier forming a Radioactive Waste Package (RWP) in order to protect the environment. It is important to study the efficiency of this mortar barrier for long term and safety assessment have to investigate the case of crack mortar formation as radioactive particles could then migrate in the cracks.
The LECD laboratory investigated this problematic by measuring the migration of CeO2 particle in mortar cracks using X-Ray microtomography. The cracks were synthesized by dissolving plastic molds (designed by 3D printing). This study showed the influence of particle interactions with tortuosity and roughness of the crack, but was limited to 40 µm particle diameter.
The aim of the postdoctoral work is to develop an experimental approach similar to the method developed to study the efficiency of HEPA filters, with particles of 0.05 - 5 µm diameter. Quantitative measurements will be performed on the particle flows on both sides of the cracked mortar sample. LECD has acquired an aerosol generator, a light-scattering aerosol spectrometer system for particle size analysis and concentration determination and an Universal Scanning Mobility Particle Sizers. The researcher will also develop modelling work using numerical tools as STARCCM+.
This project will be carried out under the format of an 12-month fixed-term contract at the Atomic Energy and Alternative Energies Commission (CEA), at the Cadarache site (Saint-Paul-lez-Durance, 13) at the Expertise and Destructive Characterization Laboratory (LECD) of the Expertise and Characterization CHICADE Service (SECC).
Contacts: ingmar.pointeau@cea.fr (R&D engineer) – Olivier.vigneau@cea.fr (Head of the Laboratory)
Sizing and control optimisation of a hydrogen production system coupled with an offshore wind farm
Coupling MRE (Marine Renewable Energy) and hydrogen sectors reveal an important potential long-term assets. The MHyWind project suggests to estimate the energetic and economic potential of a hydrogen production system integrated into a substation of an offshore wind farm. The hydrogen produced and stored locally will be distributed by boat for harbour uses, as a replacement of fossil fuels. For that purpose, it will be organized a simulation which will integrate all the energy chain towards the harbour uses of hydrogen. It will allow to estimate various configurations and sizing according to the local uses, valuation leverages, control modes and behavior of the system. The criteria will be the producible (kg of H2 producted and used) and complet costs (CAPEX and OPEX). The objective of the postdoctoral student will be to develop the simulation tool on this applicative being fully integrated with the teams of concerned laboratories.