Development of piezoelectric resonators for power conversion
CEA-Leti has been working to improve energy conversion technologies for over 10 years. Our research focuses on designing more efficient and compact converters by leveraging GaN-based transistors, thereby setting new standards in terms of ultra-fast switching and energy loss reduction.
In the pursuit of continuous innovation, we are exploring innovative paths, including the integration of piezoelectric mechanical resonators. These emerging devices, capable of storing energy in the form of mechanical deformations, offer a promising perspective for increased energy density, particularly at high frequencies (>1 MHz). However, the presence of parasitic resonance modes impacts the overall efficiency of the system. Therefore, we are in need of an individual with skills in mechanics, especially in vibrational mechanics, to enhance these cleanroom-manufactured micromechanical resonators.
You will be welcomed in Grenoble within a team of engineers, researchers and doctoral students, dedicated to innovation for energy, which combines the skills of microelectronics and power systems from two CEA institutes, LETI and LITEN, close to the needs of the industry (http://www.leti-cea.fr/cea-tech/leti/Pages/recherche-appliquee/plateformes/electronique-puissance.aspx).
If you are a scientifically inclined mind, eager to tackle complex challenges, passionate about seeking innovative solutions, and ready to contribute at the forefront of technology, this position/project represents a unique opportunity. Join our team to help us push the boundaries of energy conversion.
References : http://scholar.google.fr/citations?hl=fr&user=s3xrrcgAAAAJ&view_op=list_works&sortby=pubdate
Manufacturing of analytical microsystems by thermoplastics micro-milling
Micro-fabrication techniques and especially micro-milling can be used to manufacture microsystem prototypes with a timescale of days, as close as possible to the application. Polymethylmethacrylate (PMMA - Commercial name Plexiglas) is a commonly used material for microsystems fabrication, limited however by its chemical incompatibility with acids and solvents.
The goal of this post-doctoral project is to study the feasibility of machining thermoplastic materials other than PMMA and to optimise the associated manufacturing parameters. The post-doctoral project will start with the selection of materials in line with the aimed applications (optical and physico-chemical properties). The materials will be selected among the thermoplastics family (PC, POM, PS, HDPE, PEEK, PVC, PP, PTFE, ULTEM, etc).
The optimisation of the micro-milling step will be realized by varying parameters such as the tool rotation speed, the feed rates, the depth of cut, etc. The surfaces and channels will be characterized by optical or mechanical profilometry, optical microscopy and/or scanning electron microscopy.
Seismic behavior of an overhead crane
Overhead cranes are part of the equipment in industrial installations to which special attention must be paid. They are generally located in the upper part of buildings and are potentially subject to significant levels of acceleration in the event of an earthquake, due to the amplification induced by the supporting structure. Consequently, they are potentially subjected to significant forces and can be the source of significant forces on the supporting structure. This study is a continuation of two previous test campaigns carried out on the Azalée shaking table of the EMSI laboratory, on a mock-up of an overhead crane. It aims to provide validated numerical models of this kind of equipment. Two lines of research are considered. The first axis aims to complement the “historical” test campaigns with static tests to justify the adjustment of the numerical models. The second axis consists of exploiting, by comparison tests/calculations, all of the tests that were carried out as part of a previous test campaign for statistical analysis purposes.
HPC simulation of electrode mechanical properties in Li-ion batteries
Li-ion batteries are complex multi-physics systems in which chemical reactions, transport phenomena, and mechanical deformation are strongly coupled. The battery electrodes are composed of micrometric granular materials (the microstructure) where the lithium can insert and disinsert, a process that creates internal mechanical stress and strain in the materials and subsequent volumic changes. While it is currently observed that the coupling between electrochemical reactions and mechanical deformation at the microstructure level strongly impacts the battery performances, lifespan and safety, the origin of this impact is poorly understood. The global objective of this position is to better understand the coupling between mechanical deformations of the microstructure and the local conditions of lithium transport in the electrode. The study should lead to practical applications such as recommendation on the electrode design to increase life capability of Li-ion batteries.
Direct electrification of innovative reactors for reverse water gas shift (RWGS)
Technologies such as direct electrification and use of clean hydrogen could play a role in defossilizing energy sector and chemical industries. Anyway, for some specific areas, like maritime or aviation transport or carbon based chemical intermediates production, it will be necessary to replace fossil molecules by renewable ones. Reverse water gas shift (RWGS), consisting in a catalytic hydrogenation of highly stable CO2 molecule into a more common CO rich syngas , is a key for a retrofit of various fossil based infrastructure. Indeed, such syngas is used in chemical industry for about a century to synthesize chemicals and fuels.
Anyway, RWGS being an endothermal equilibrated reaction favoured at high temperature, the thermal management of the reaction is still an issue, particularly the heat input to the reactor, which in this context should be efficient and from a decarbonized source.
Modeling of laser-matter interaction for hypervelocity impact simulation
Hypervelocity impacts (HVI) are an important issue for various aerospace, geophysical or large laser facility protection applications such as the Laser Megajoule. In these applications, impact speeds can range from a few km/s to tens of km/s. Below 10 km/s, gas or powder guns can be used to launch projectiles at representative speeds. For higher velocities (10 to 50 km/s), the use of laser-generated shocks is an interesting alternative.
However, the analogy between HVI and laser shocks relies on a good modeling of the laser-matter interaction mechanisms, and in particular of the 2D effects that affect the pressure field at the target surface.
The objective of this postdoctoral fellowship is to study the laser-matter interaction with numerical tools developed at the CEA, in particular the 1D code Esther and the 2D/3D code Troll. The simulations will be validated by comparison with experimental data and will then be used to conduct parametric studies on the spatial and temporal profiles of the laser beam.
Earthquake effect on underground facilities
The Industrial Centre for Geological Disposal (Cigeo) is a project for a deep geological disposal facility for radioactive waste to be built in France. These wastes will be put in sealed packages in tunnels designed at 500 meters depth. The seals are made of a bentonite/sand mixture which has a high swelling capacity and a low water permeability. As a part of the long-term safety demonstration of the repository, it must be demonstrated that the sealing structures can fulfill their functions under seismic loads over their entire lifetime. In order to guarantee this future nuclear waste repository, CEA and Andra are collaborating to work on the potential scientific and engineering challenges involved.
The responses of underground repository to earthquake events are complex due to the spatially and temporally evolving hydro-mechanical properties of the surrounding media and the structure itself. Accurate modeling of the behavior, therefore, requires a coupled multiphysics numerical code to efficiently model the seismic responses for these underground repositories within their estimated lifespan of 100 thousand years.
The research will therefore, propose a performance assessment for sequential and parallel finite element numerical modeling for earthquake analysis of deep underground facilities. Then perform a synthetic data sampling to account for material uncertainties and based on the obtained results in the previous assessment, run a sensitivity analysis using a FEM or a metamodeling process. Finally, the results and knowledge gained within the span of this project will be processed and interpreted to provide responses for industrial needs.
Robust path-following solvers for the simulation of reinforced concrete structures
Path-following procedures are generally employed for describing unstable structural responses characterized by ``snap-backs'' and/or ``snap-troughs''. In these formulations, the evolution of the external actions (forces/displacements) is updated throughout the deformation process to fulfill a given criterion. Adapting the external loading during the calculation to control the evolution of the material non-linearities is helpful to obtain a solution and/or to reduce the number of iterations to convergence. This second aspect is of paramount importance, especially for large calculations (at the structural scale). Different path-following formulations were proposed in the literature. Unfortunately, an objective criterion for choosing one formulation over another for the simulation of reinforced concrete (RC) structures (in the presence of different and complex dissipation mechanisms) still needs to be made available. The proposed work will focus on the formulation of path-following algorithms adapted to simulate RC structures.
Multiphysics modeling of an experimental sintering furnace
In the scope of the development and improvement of the performance of low-carbon energy sources, the CEA has a software platform for modeling the behavior of nuclear fuel from its manufacture to its use in the reactor. Sintering, a key step in fuel fabrication is the heat treatment process used to consolidate and densify nuclear fuel to form the solid solution U1_yPuyO2-x. The sintering cycle generally comprises a rise in temperature with a linear ramp, a constant temperature plateau and a controlled cooling, with possibly a continuous adaptation of the oxygen potential through the oxidation-reduction buffer imposed by the H2 over H2O ratio of the carrier gas to reach the target oxygen-metal ratio. A first modeling of an industrial sintering furnace was carried out using the OpenFOAM software suite and the C++ finite elements library DIFFPACK. A second step aims to validate the models used in the simulation of this industrial furnace based on a separate effects approach and the modeling of a laboratory sintering furnace. This post-doctorate will be carried out at CEA Cadarache within the multiscale modeling laboratory (LM2Cà of the fuel studies department. This work will be carried out in close collaboration with the teams of experimenters from the Solid Chemistry and Actinide Materials Development Laboratory (LSEM) of CEA Marcoule who are developing and operating the experimental furnace. The collaboration will focus on the modeling input data (furnace geometry, temperature and atmospheric conditions) and the measurements to be compared with the simulation data. The post-doctoral student will evolve in a stimulating environment, within a dynamic laboratory where about fifteen doctoral and post-doctoral students are already working, in contact with experts in fuel physics modeling and in collaboration with experimenters. The work can be enhanced by presentations at conferences and the writing of articles.
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).