Thermo-aeraulic numerical simulation of an incineration reactor
An incineration and vitrification process devoted to the treatment of apha contaminated organic/metallic wastes originating from MOX production facilities is currently under development at the LPTI laboratory (Laboratoire des Procédés Thermiques Innovants) from the CEA of Marcoule. The development program relies on full scale mock-up investigation tests as well as 3D numerical simulation studies.
The thermo-aeraulic model of the incinerator reactor, developed with the Ansys-Fluent commercial software, is composed of several elementary bricks (plasma, pyrolysis, combustion, particle transportation).
The proposed work consists in improving the model, in particular as regards the pyrolysis and combustion components : chemical reactions, unsteady process… The degree of representativeness of the model will be assessed on the basis of a comparative study using experimental data coming from experiments carried out on the prototype reactor. Besides this development work, various parametric studies will be performed in order to evaluate the impact of various reactor design modifications.
So as to investigate the radiologic behaviour of the reactor during incineration of alpha contaminated wastes, a particle transport model (DPM) associated to a parietal interaction model will be implemented. The simulation results will be compared to experimental data obtained from the analysis of deposits collected on reactor walls (experimental tests are performed with actinides inactive surrogates).
Development and optimization of adaptive mesh refinement methods for fluid/structure interaction problems in a context of high performance computing
A new simulation code for structural and compressible fluid mechanics, named Manta, is currently under development at the french CEA. This code aims at both unifying the features of CEA’s legacy implicit and explicit codes and being natively HPC-oriented. With its many numerical methods (Finite Elements, Finite Volumes, hybrid methods, phase field, implicit or explicit solvers …), Manta enables the simulation of various static or dynamic kinds mechanical problems including fluids, structures, or fluid-structure interactions.
When looking for optimizing computation time, Adaptive Mesh Refinement (AMR) is a typical method for increasing numerical accuracy while managing computational load.
This postdoctoral position aims at defining and implementing parallel AMR algorithms in a high performance computing context, for fluid/structure interaction problems.
In a preliminary step, the functionalities for hierarchical AMR, such as cell refinement and coarsening, field transfers from parents to children cells, refinement criteria or hanging nodes management, will be integrated in Manta. This first work will probably rely on external libraries that should be identified.
In a second step, the distributed-memory parallel performances will be optimized. Especially, strategies for load balancing between the MPI processes should be studied, especially for fluid/structure interaction problems.
Finally, especially for explicit in time computations, one will have to define and implement spatially adapted time stepping to cope with the several levels of refinement and the different wave propagation velocities.
These last 2 points will give rise to some publications in specialized scientific journals.
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.
Detection of cyber-attacks in a smart multi-sensor embedded system for soil monitoring
The post-doc is concerned with the application of machine learning methods to detect potential cyber-security attacks on a connected multi-sensor system. The application domain is the agriculture, where CEA Leti has several projects, among which the H2020 project SARMENTI (Smart multi-sensor embedded and secure system for soil nutrient and gaseous emission monitoring). The objective of SARMENTI is to develop and validate a secure, low power multisensor systems connected to the cloud to make in situ soil nutrients analysis and to provide decision support to the farmers by monitoring soil fertility in real-time. Within this topic, the postdoc is concerned with the cyber-security analysis to determine main risks in our multi-sensor case and with the investigation of a attack detection module. The underlying detection algorithm will be based on anomaly detection, e.g., one-class classifier. The work has tree parts, implement the probes that monitor selected events, the communication infrastructure that connects the probes with the detector, and the detector itself.
Data science for heterogeneous materials
In order to predict the functional properties of heterogeneous materials through numerical simulation, reliable data on the spatial arrangement and properties of the constitutive phases is needed. A variety of experimental tools is commonly used at the laboratory to characterize spatially the physical and chemical properties of materials, generating "hyperspectral" datasets. A path to progress towards an improved undestanding of phenomena is the combination of the various imaging techniques using the methods of data science. The objectives of this post-doc is to enrich material knowledge by developping tools to discover correlations in the datasets (for exemple between chemical composition and mechanical behavior), and to increase reliability and confidence in this data by combining techniques and physical constraints. These tools will be applied to datasets of interest regarding cementitious materials and corrosion product layers from archaeological artifacts.
Simulation of supercritical helium flows in the cooling circuits of tokamaks
Future fusion reactors such as tokamaks (ITER, DEMO) will have to demonstrate the safety of their systems, validated by thermal hydraulic codes. To meet this requirement, the CATHARE code has been chosen as scientific computing tool. The work will consist in adapting the CATHARE code to helium at low temperatures and then to benchmark it with other thermal hydraulic codes used by the DRF (Direction de la Recherche Fondamentale), as well as with experimental data available at CEA Grenoble.
The study will be threefold. The first phase will be dedicated to a literature survey on the thermal hydraulics of helium, featured by closing equations for monophasic helium (friction and heat transfer coefficients). In a second step, the engineer will implement these laws in the code and perform some validations tests. The last part will focus a benchmark based on three applications: the study of a cryo-pump, the study of a supercritical helium discharge and the study of a superconducting cable.
Hardening energy efficient security features for the IoT in FDSOI 28nm technology
The security of the IoT connected objects must be energy efficient. But most of the work
around hardening by design show an additional cost, a multiplying factor of 2 to 5, on the
surface, performance, power and energy, which does not meet the constraints of the IoT.
Last 5 years research efforts on hardening have been guided by reducing silicon area or
power, which do not always imply a decrease in energy, predominant criterion in autonomous
connected objects. The postdoc topic addresses the hardening and energy consumption
optimization of the implementation of security functions (attack detection sensors,
cryptographic accelerator, random number generator, etc.) in 28nm FDSOI technology.
From the selection of existing security bricks, unhardened in FPGA technology, the postdoc
will explore hardening solutions at each step of the design flow in order to propose and
to validate, into a silicon demonstrator, the most energy efficient countermeasures that
guarantee a targeted security level.
To achieve those goals, the postdoc can rely on existing methodologies of design and of
security evaluation thanks to test benches and attack tools.
Numerical quality analysis of simulation codes with CADNA, Verificarlo and Verrou
Numerical codes rely on floating-point arithmetic to represent real numbers and the operations applied to them. However, in general, real numbers cannot be exactly represented by floating-point numbers. The finite precision of the floating-point arithmetic may lead to round-off errors that may accumulate. With the increasing computational power, the algorithm complexification and the coupling of numerical codes, it is crucial to quantify the numerical robustness of an application or an algorithm.
CADNA [1], Verificarlo [2] and Verrou [3] are dedicated tools that allow estimating the round-off errors propagation and measuring the numerical accuracy of the obtained results. The objective of this work is to use these three tools on GYSELA [4, 5], a simulation code used to characterize the plasma dynamics in Tokamak, and PATMOS [6], a mini-app representative of a Monte Carlo neutron transport code. This analysis will be aimed at assessing the numerical robustness of these two applications or some of their algorithms. In addition to the analysis of the numerical quality, these tools will also be used to see whether it is possible to lower the precision (simple or even half precision instead of double) of some algorithms, thus improving the memory footprint and/or performances (vectorization, communications). Beyond the lessons learnt on the two analyzed codes, a second objective will be the elaboration of a methodology that could be more generic and be applied more broadly to other codes.
Development of multiphysics tools dedicated to the modeling of FSR and associated studies.
The sodium group of DM2S (department of CEA Saclay) develops numerical coupling tools in order to realize accidental case studies (fast transient). The physical domains concerned are neutronics, thermo-hydraulics and mechanics. The subject of this post-doc deals within this framework.
The aim is to carry out several studies: the integration of a coupling within the CORPUS platform, to carry out studies in order to test (and introduce) in the coupling the impact of the deformation of the assemblies by the Temperature on the flow of liquid sodium, the use of the neutronic cross sections generated by the code APOLLO3, the study of other accidental cases, and extend the modeling to the subchannel and pin scales.