Missions

The work will focus on passive structural health monitoring of structures immersed in heavy fluids, by continuing to develop the “Modal Strain Energy” and “Matched Field Processing” methods for detecting and locating a potential defect in operational condition, in collaboration between LMA researchers from the “Waves and Imaging” and “Sound” teams, and the LISM laboratory at CEA Cadarache.
This research project is a continuation of previous thesis work (defended at LMA in December 2024) on “Low-frequency passive imaging”. This work follows several studies on the subject (theses, internships and contracts) over a period of more than 10 years.

Activités

General context :
With the aim to monitor the structural health of nuclear reactor vessels, the overall goal of this work is to develop methods for the passive detection and localization of a structure's mechanical properties, based on vibrations generated by ambient noise in the reactor. Noise sources in the reactor can be of various origins. Given the lack of knowledge or the difficulty in determining the nature of the ambient noise in the reactor (spectrum, spatial and temporal distributions, levels), the approach consists in developing passive methods by determining their conditions of use but not referring to a particular configuration with a specific noise spectrum.
Work to date has focused on developing methods for monitoring structures for two types of ambient noise: noise from acoustic sources and noise from mechanical/vibratory sources. Two methodologies for monitoring the state of health of a structure based on an experimental modal analysis of the structure have been proposed:
- the detection and localization of a potential local fault using the Modal Strain Energy (MSE) method, based on the analysis of modal deformations resulting from modal identification,
- or alternatively, the detection and localization of a potential fault using the Matched Field Processing (MFP) method, based on the reconstruction of a response model of the inspected structure from the modal parameters predicted by modal identification.
The approaches were tested in light fluids by decoupling the analysis of random ambient noise from mechanical and acoustic sources.
The aim of the present post-doctorate is to continue this work on the development of the Modal Strain energy (MSE) and Matched Field Processing (MFP) methods for detecting and locating a potential fault on several geometries of heavy fluid structures and for configurations of unknown random sources closer to operational conditions. This research work will be published in scientific journals.
Methodology and plan of work
The study has three components:
- operational modal analysis to extract the modes of the probed medium,
- algorithmic and experimental developments on the MSE method
- and algorithmic and experimental developments on the MFP method.
- The work aims to consider the parsimonious aspect of measurement points
The work envisaged is as follows:
- Implementation of vibration experiments in a tank
- Conduct of operational modal analysis for more geometries and with a reduced number of sensors
- Implementation of the MSE method on a cylindrical structure immersed in water and sensitivity analysis
- Algorithmic and experimental developments on the MFP method with reconstruction of the vibration response from vibration and acoustic measurements.

Compétences

- PhD thesis in acoustics, mechanics
- Skills in structural acoustics, signal processing, antenna processing
- Ability and interest in conducting experiments in a controlled environment (tank experiments)
- Knowledge of Matlab or Python required
- Knowledge of numerical simulation software such as Comsol Multiphysics would also be appreciated
- Excellent proficiency in English
- Ability to work in a team and spirit of initiative

Contexte de travail

The LMA is a joint AMU-CNRS-Centrale Méditerranée research unit (UMR 7031) affiliated to Aix-Marseille Université (AMU), CNRS and Centrale Marseille (ECM).
The LMA employs around 110 people, including 70 permanent staff and some 40 PhD students/post-doctoral researcher. The LMA has nationally and internationally recognized skills in the fields of Solid Mechanics and Acoustics.
This post-doctoral project is part of the MISTRAL joint laboratory between LMA/Aix-Marseille Université/CNRS/Centrale Marseille and CEA, which aims to anticipate, prevent and remedy as far as possible the failures of complex multi-scale systems hosting multi-physical phenomena, in order to increase their safety under operational conditions. The post-doctoral fellow will join the “Waves et Imaging” team and will also work in collaboration with researchers from the “Sound” team and the LISM laboratory at CEA Cadarache, a partner in this research project. This job will be carried out at LMA (Marseille) and CEA (Cadarache).

Contraintes et risques

The candidate will be required to travel to the CEA Cadarache site over several days to set up and run experiments in one of the CEA's tanks.