Development of a computational framework dedicated to model order reduction by certified reduced basis method.
Many engineering fields require to solve numerically partial differential equations (PDE) modeling physical phenomenon.
When we focus on a mathematical model that describes the physical behavior of a system based on one or more parametrized PDEs (geometrical or physical parameters), it may be desirable to rapidly and reliably evaluate the output of the model (quantity of interest)
for different parameter values.
The real-time context, needed to perform command-control, and contexts asking many evaluations of model outputs (typically for optimization methods or uncertainty and sensitivity analysis) lend themselves perfectly.
The certified reduced basis method is an intrusive reduction method beacause, unkike non-intrusive methods, the reduction is based on the projection of operators associated to physical model PDEs.
This method allow to obtain rapidly, for a given set of parameter values, an approximation of the evaluation of the model output.
One of the strengths of the method is the "certified" aspect to estimate the approximation error of the model output evaluation.
The goal of the post-doctorate is to develop a computational framework for the certified reduced basis method. This framework should be based on the TRUST platform (https://sourceforge.net/projects/trust-platform/) developed at CEA and will be generic enough to be used to deal with different types of problems (linear or not, stationary or not, coercive or not...)
The framework will be used in the case of a two-fluid mixing model.
Conversational Agent for Medical Serious Games
The LVIC laboratory participates in a research project which aims to develop innovative tools for teaching medical students. The training will be done through serious games of second generation, in which the learner can interact directly with the environment:
- immersed in a 3D environment with a Virtual Reality Head Mounted Display and motion detection,
- with natural and ecological handling of the environment (instruments, patient …),
- and a voice interaction with conversational and emotional avatars.
The multimedia team of LVIC laboratory is involved in the project to develop tools allowing students to interact in natural language with conversational avatars.
In this context, the post-doctoral researcher will be in charge of:
- studying the state of art of conversational agents;
- understanding and mastering the technological components of the laboratory language processing;
- proposing and developing a dialogue system allowing interaction in natural language with conversational avatars of the project.
Application of ontology and knowledge engineering to complex system engineering
Model-Based System Engineering relies on using various formal descriptions of the system to make prediction, analysis, automation, simulation... However, these descriptions are mostly distributed across heterogeneous silos. The analysis and exploitation of the information are confined to their silos and thereby miss the big picture. The crosscutting insights remain hidden.
To overcome this problem, ontologies and knowledge engineering techniques provide desirable solutions that have been acknowledged by academic works. These techniques and paradigm notably help in giving access to a complete digital twin of the system thanks to their federation capabilities, in making sense to the information by embedding it with existing formal knowledge and in exploring and uncovering inconsistencies thanks to reasoning capabilities.
The objective of this work will be to propose an approach that gives access to a complete digital twin federated with knowledge engineering technologies. The opportunities and limits of the approach will be evaluated on industrial use cases.
Cluster dynamic simulations of materials under irradiation
Alloys used in nuclear applications are subjected to neutron irradiation, which introduces large amounts of vacancy and interstitial defects. Over time, these defects migrate, recombine and agglomerate with minor alloying elements to form small clusters. This affects the mechanical properties of ferritic steels and weakens them. In this context, the microstuctural evolution is to be simulated using the rate equation cluster dynamic method. However, this approach becomes ineffecient when several minor alloying elements need being taken into account. The difficulty comes from the huge number of cluster variables to describe. The project aims at optimizing the code efficiency on a distributed parallel architecture by implementing parallelized vector and matrix functions from SUNDIALS library. This library is used to integrate the ordinary differential equation describing the reactions between clusters. Another aspect of the work is more theoretical and involves reformulating the non-linear root-finding problem by taking advantage of the reversibility of most chemical reactions. This property should facilitates the implementation of direct and gradients iterative sparse solvers for symmetric definite positive matrices, such as the multi-frontal Cholesky factorization and the conjugate gradient methods, respectively. One avenue of research will consists of combining direct and iterative solvers, using the former as a preconditioner of the latter.
New reference radiation field for radioprotection in the range of Cs-137 et Co-60 using an electrostatic electron accelerator
During the last years, LNHB has started and realized a research program in order to produce a reference photon radiation field for the radioprotection needs at high energies (~6 MeV) using its medical electron accelerator Saturne 43. For this purpose, a target and its appropriate flattering-attenuating filter have been designed by LNHB in order to produce the required photon field.
Nowadays there is no existing device able to produce radiation fields from an accelerator in the Cs-137 and Co-60 equivalent energy range. In order to achieve this, one needs the technology to construct and properly use absolute dosemeters for photons (cavity ionization chambers), to determine the right target-filter assembly allowing the production of the required photon field and to accurately calculate the conversion factors from air-kerma to operational quantity which is the dose-equivalent using the spectral distribution at the calibration position.
The candidate will participate in the construction of cavity ionization chambers needed for the characterization in terms of dose-equivalent of radiation field obtained from the electron accelerator and to the on-site measurements. He(She) will also be in charge with Monte-Carlo simulations in order to optimize the target-filter assembly used to produce the reference photon field from an electrostatic accelerator.
Software and hardware combined acceleration solution for operations research algorithms
The purpose of the study is to prepare the next generation of OR solvers. We will study the hardware acceleration possibility based on FPGA to run some or all of the OR algorithm. The blocks for which such a solution is not effective can be parallelized and executed on a standard computing platform. Thus, the proposed runtime correspond to a standard computing platform integrating FPGA. To access to this platform we require a set of tools. These tools should provide features such as (a) analysis and pre-compiling an input or problem or sub-problem of OR, (b) HW / SW partitioning and dedicated logic optimization and finally (c) generating an software executable and a bitstream.
The first step will be to find OR algorithms that are well suited for hardware acceleration. We then propose a HW / SW partitioning methodologies for different classes of algorithms.
The results will be implemented to lead to a compilation prototype starting from an OR instance and generating a software executable and a bitstream. Theses results will be implemented and executed on a computing platform integrating FPGA to evaluate the performance gain and the impact on the energy consumption of the proposed solution.
Simulation of PEMFC flooding phenomena
The proton exchange membrane fuel cell (PEMFC) is now considered as a relevant solution for carbon-free electrical energy production, for both transport and stationary applications. The management of the fluids inside these cells has a significant impact on their performance and their durability. Flooding phenomena due to the accumulation of liquid water are known to impact the operation of the cells, causing performance drops and also damages that can be irreversible. With the use of thinner channels in ever more compact stacks, these phenomena are becoming more and more frequent. The objective of this post-doc is to progress in the understanding of flooding in PEMFCs. The work will consist in analyzing the link between the operating conditions, the design of the channels and the materials used in the cell. It will be based on a two-phase flow modeling approach at different scales, from the local scale at the channel-rib level, up to, via an upscaling approach, the level of the complete cell. The study will also be based on numerous experimental results obtained at the CEA or in the literature.
High entropy alloys determination (predictive thermodynamics and Machine learning) and their fast elaboration by Spark Plasma Sintering
The proposed work aims to create an integrated system combining a computational thermodynamic algorithm (CALPHAD-type (calculation of phase diagrams)) with a multi-objective algorithm (genetic, Gaussian or other) together with data mining techniques in order to select and optimize compositions of High entropy alloys in a 6-element system: Fe-Ni-Co-Cr-Al-Mo.
Associated with computational methods, fast fabrication and characterization methods of samples (hardness, density, grain size) will support the selection process. Optimization and validation of the alloy’s composition will be oriented towards two industrial use cases: structural alloys (replacement of Ni-based alloys) and corrosion protection against melted salts (nuclear application)
Apprenticeship Learning Platform deployment for industrial applications
This project aims at developing a demonstrator that integrates state-of-the-art technologies and improve it on a use-case representative of the industrial world.
The demonstrator will consist in a robotic / cobotic arm coupled to an acquisition sensor (RGBD type). This device will be positioned in a workspace made of a rack / shelf containing objects / pieces of various shapes and qualities (materials, densities, colors ...) in front of which will be placed a typical conveyor prototype of industrial installations. The type of tasks expected to be carried out by the demonstrator will be "pick and place" type tasks where an object will have to be identified in shelf and then placed on the conveyor.
This type of demonstrator will be closer to the real industrial conditions of use than the "toy" examples used in the academic field.
This demonstrator will focus first on the short-term effectiveness based on state of the art technologies for both hardware and software, for a use case representative of the industrial world.
At first, it will thus be less focused on the evolution of the algorithms used than on the adaptation of the parameters, the injection of knowledge a priori dependent on the context making it possible to reduce the high-dimensional input space, etc.
Nonlinear ultrasonic testing for the assessment of adhesive bonding properties
The CEA-LIST carries out Non Destructive Testing (NDT) projects in partnership with various industrial sectors. A strong collaboration with Airbus Group Innovations (AGI) had led to a common entity through the NDT laboratory for Aeronautics Applications (LC2A).
With the increasing portion of composite materials in the aerospace industry, assessment of the adhesive bonding properties of such composite structures is a key issue. Various aspects could decrease the quality of bonding, such as the surface contamination, non-optimal thermal cycle or external mechanical stresses. However, conventional NDT techniques are often not sensible to such damages in the adhesive bonds.
Non-linear ultrasonic methods such as wave mixing, harmonic generation or non- linear imaging appear as promising techniques to detect kissing bonds and pre-damaging that could occur in adhesive bonds. The objective of this postdoc position is to develop NDT innovative solutions for the assessment of the adhesion quality by means of experimental techniques based on such non-linear methods.
This post-doc position will be carried out in the framework of an international research program on the adhesion bonding. The candidate will work in the NDE laboratory for Aeronautics Applications located in Toulouse. Strong skills in experimental physics, instrumentation, and non-linear ultrasonics would be appreciated.