Development of an innovative method for ultrasound imaging of velocity fields in flows behind opaque walls
Today, the only solutions on the market for measuring 2D velocity fields are laser-based optical methods (such as particle imaging velocimetry: PIV).
These are limited by the need for optical access to the flow and are therefore inapplicable on opaque fluids (such as liquid metals) or through opaque pipes (such as metal pipes, the majority in industry).
To overcome this limitation and meet new challenges (in research and industry) it is possible to rely on acoustic imaging methods.
The LISM (CEA Cadarache Instrumentation Laboratory) has been working for several years on the development of an industrial acoustic PIV (or echo-PIV) method.
An initial thesis has led to significant progress, and the CEA is now planning to market echo-PIV scanners through a start-up project.
However, there are still a number of hurdles to overcome, in particular that of imaging through walls with high acoustic impedance differences.
Your main objective will be to remove these obstacles. This mission will be structured as follows:
- Bibliographical study and familiarisation with the echo-PIV method
- Numerical study and development of a solution to resolve the problems of energy transmission through the metal wall
- Experimental validation of the detection of microscopic reflectors through a metal wall
- Numerical study and development of a solution to the problem of multiple reflection within the metal wall, leading to poor reconstruction of the final image
- Experimental validation of the solution to the reflection problem
- Adaptation of the acoustic imaging method to simultaneously resolve the transmission and reflection problems
- Publication in scientific journals (and/or patents)
Improvement and extension of a phase-field model for the 3D simulation of important phenomena in the behavior of lithium-ion batteries
In order to optimize the charging time of current-generation batteries, or increasing the power density for future generations, the study of the behavior of materials is crucial to master the lithiation mechanisms of intercalations materials. (e.g. graphite) or “stripping/plating” of lithium metal. In this context, the use of phase field numerical simulations is booming; these methods lend themselves to the modeling of dynamic phenomena for multiphase and multiconstituent systems.
Recently, a 2D phase field module from TrioCFD (open-source software developed at CEA and based on the TRUST platform) was generalized to an arbitrary number of constituents or phases. This post-doctoral project aims to improve and extend this TrioCFD module to high-performance 3D simulations in a distributed parallel computing environment. The objective is to use this module to simulate the 3D physical behaviors of interest of the aforementioned lithium-ion battery materials. We will rely on recent 2D phase field work which has provided a certain number of original and relevant answers to these issues. The move to 3D simulations will provide essential scientific perspectives for these applications.
This work will be carried out as part of a collaboration between several CEA teams from the Cadarache, Grenoble and Saclay centers, bringing together varied expertise (behavior of lithium-ion batteries, phase field method, TrioCFD software environment and numerical methods).
Modelling of valley winds by statistical downscaling
To model and monitor atmospheric emissions in an area with significant relief, it is essential to represent the winds at the scale of this relief. Cadarache's operational meteorological model only has a horizontal resolution of 1km, which does not allow it to resolve the orographic effects of the valley.
However, obtaining simulation results with a high resolution model requires calculation times that are still incompatible with the constraints of operational weather forecasting (6 hours of calculation on our servers for 1 hour of forecast for Cadarache in 2020). This constrains the horizontal resolution of the calculations and does not make it possible to resolve the orographic valley effects.
The object of the post-doc is therefore to develop a downscaling model applied to a 3D mesh of the valley, with a sufficient resolution to, at the same time, model the aerology of the valley and follow a pollution plume using an atmospheric dispersion model. It will be implemented through the use of an artificial neural network, the learning of which will be based on measurements of local climatology and aerology, supplemented by synthetic data using a local high-resolution model.
The candidate will work within a small, attentive and benevolent CEA team while remaining connected to university research via the Toulouse Aerology Laboratory. He will be able to both become a specialist in applied research in the meteorological field and acquire digital and scientific skills that can be used in business.
Development of processing by Artificial Intelligence of a measuring and forecasting station
This post-doctoral proposal is part of the French atomic commission (CEA) project "MultiMod'Air", which involves developing an « intelligent » prototype of air quality measurement and forecasting station within two years. The work proposal is to develop the bricks of Artificial Intelligence (AI) of the project: correction by ANN (Artificial Neuronal network) of the measurements obtained through low cost sensors, correction ANN of weather forecasts at the station level, which are simple treatments to implement. The actual research work will concern the development of a AI based pollution forecast at the station by learning from past events.
Development of Monte-Carlo methods for the simulation of radiative transfer: application to severe accidents
This post-doctoral subject concerns the development of Monte-Carlo ray-tracing methods for modeling radiation heat transfer in the context of severe accidents. Starting from a well-developed software framework for Monte Carlo simulation of particle transport in the context of reactor physics and radiation protection, we will seek to adapt existing methods to the problem of radiative heat transfer, in a high-performance computing framework. To do this, we will develop a hierarchy of approximations associated with radiative heat transfer that are intended to allow the validation of simplified models implemented in the context of the numerical simulation of severe accidents in nuclear reactors. Focusing on algorithm and simulation performance, this work is intended to be a "proof of principle" of the possible software mutualization around the Monte-Carlo method for particle transport on the one hand and radiative heat transfer on the other hand.