Ifsttar PhD subject

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Title : Imaging of uni-axial elastic waveguides by sensitivity methods

Main host Laboratory - Referent Advisor GERS - GeoEND  -  TREYSSEDE Fabien      tél. : +33 240845932

Director of the main host Laboratory DEROBERT Xavier  -

PhD Speciality Acoustique

Axis of the performance contract 2 - COP2017 - More efficient and resilient infrastructure

Main location Nantes

Doctoral affiliation UNIVERSITE DU MAINE LE MANS

PhD school Sciences de l'Ingénierie et des Systèmes (SIS)

Planned PhD supervisor TREYSSEDE Fabien  -  Université Gustave Eiffel  -  GERS - GeoEND

Planned PhD co-supervisor LAGUERRE Laurent  -  Université Gustave Eiffel  -  GERS - GeoEND

Planned financing Contrat doctoral  - Ifsttar

Abstract

Guided waves can propagate over long distances with little loss of energy. They are of potential interest for the non-destructive evaluation and structural health monitoring of slender civil engineering structures (cables, bars, etc.). However, the development of robust monitoring methods faces several challenges. On the one hand, civil engineering structures are usually partially or completely buried in an infinite environment. They are often only accessible to one of their end. On the other hand, the multimodal and dispersive nature of guided waves complicates the interpretation of measurement results, so that their exploitation requires propagation models. In this field, significant progress has been made in recent years at Ifsttar (formerly LCPC) through the development of original numerical modeling tools, based on finite element methods dedicated to guided waves, and taking into account various phenomena: source [1], presence of defects [2], curvature of the guide [3], prestress [4], embedment in a solid matrix [5,6] …

The aim of the thesis will be to develop an imaging method that takes into account both the difficulty of access to the structure (limited number of transducer positions) and the complex nature of guided wave propagation. Based on the theory of inverse problems in elastodynamics, the approach will consist in evaluating a gradient revealing the sensitivity of a cost functional to some parameters of the medium. The evaluation of this gradient in a healthy configuration (without defects) makes it possible to obtain, without iteration, a spatial representation of the defects present in the real structure. The gradient can be calculated very quickly (in "real time") thanks to the adjoint state method combined with the modal formalism of waveguides. At present, this approach has only rarely been applied to elastic waveguides [7]. Various questions remain open such as the influence of measurement and excitation configurations (frequencies, number of sensors and their placement, noise, etc.) and the choice of the gradient according to the type of defects. To answer these questions, the PhD student will use the modeling tools available in the laboratory to implement fast-imaging methods, test them on synthetic data, and finally on real data obtained from experiments.

The PhD position will take place at the GeoEND laboratory (Geophysics and Non Destructive Evaluation) of Ifsttar, Nantes, France. The appointment will be for three years (beginning : October 2020, 1858€ gross per month for the first two years and 2165€ for the third year).

Applicants should hold a MSc or equivalent in mechanics, acoustics, physics, applied mathematics or related fields, and have a strong background in numerical methods, finite element, waves or structural dynamics. Knowledge in inverse problems and signal processing would be appreciable. We are looking for excellent and highly motivated students.

Please send a cover letter, official transcripts of the last two years, a CV with a brief statement of research experience along with the names and complete contact information of two references before April 3rd to:
fabien.treyssede@ifsttar.fr and laurent.laguerre@ifsttar.fr
https://www.ifsttar.fr/menu-haut/annuaire/fiche-personnelle/personne/treyssede-fabien/
https://www.ifsttar.fr/menu-haut/annuaire/fiche-personnelle/personne/laguerre-laurent/

Further details for the application process: https://www.ifsttar.fr/offres-theses/index.php

References:
[1] F. Treyssède, L. Laguerre, “Numerical and analytical calculations of the modal excitability for elastic wave generation in lossy waveguides”, Journal of the Acoustical Society of America 133, 3827-3837 (2013).
[2] F. Benmeddour, F. Treyssède and L. Laguerre, “Numerical modeling of guided wave interaction with non-axisymmetric cracks in elastic cylinders”, International Journal of Solids and Structures 48, 764-774 (2011).
[3] F. Treyssède, “Mode propagation in curved waveguides and scattering by inhomogeneities: application to the elastodynamics of helical structures”, Journal of the Acoustical Society of America 129, 1857-1868 (2011).
[4]. F. Treyssède, A. Frikha and P. Cartraud, “Mechanical modeling of helical structures accounting for translational invariance. Part 2: Guided wave propagation under axial loads”, International Journal of Solids and Structures 50, 1383-1393 (2013).
[5] K. L. Nguyen, F. Treyssède and C. Hazard, “Numerical modeling of three-dimensional open elastic waveguides combining semi-analytical finite element and perfectly matched layer methods”, Journal of Sound and Vibration 344, 158–178 (2015).
[6] M. Gallezot, F. Treyssède, L. Laguerre, “A modal approach based on perfectly matched layers for the forced response of elastic open waveguides”, Journal of Computational Physics 356, 391-409 (2018).
[7] S. Rodriguez, M. Deschamps, M. Castaings, and E. Ducasse, “Guided wave topological imaging of isotropic plates”, Ultrasonics 54, 1880-1890 (2014).

Keywords : acoustic, wave, guide, mode, finite elements, modeling, simulation, imaging, experimental, inverse problem, adjoint state, time reversal

Main host Laboratory - Referent Advisor	GERS - GeoEND - TREYSSEDE Fabien tél. : +33 240845932
Director of the main host Laboratory	DEROBERT Xavier -
PhD Speciality	Acoustique
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Nantes
Doctoral affiliation	UNIVERSITE DU MAINE LE MANS
PhD school	Sciences de l'Ingénierie et des Systèmes (SIS)
Planned PhD supervisor	TREYSSEDE Fabien - Université Gustave Eiffel - GERS - GeoEND
Planned PhD co-supervisor	LAGUERRE Laurent - Université Gustave Eiffel - GERS - GeoEND
Planned financing	Contrat doctoral - Ifsttar
Abstract Guided waves can propagate over long distances with little loss of energy. They are of potential interest for the non-destructive evaluation and structural health monitoring of slender civil engineering structures (cables, bars, etc.). However, the development of robust monitoring methods faces several challenges. On the one hand, civil engineering structures are usually partially or completely buried in an infinite environment. They are often only accessible to one of their end. On the other hand, the multimodal and dispersive nature of guided waves complicates the interpretation of measurement results, so that their exploitation requires propagation models. In this field, significant progress has been made in recent years at Ifsttar (formerly LCPC) through the development of original numerical modeling tools, based on finite element methods dedicated to guided waves, and taking into account various phenomena: source [1], presence of defects [2], curvature of the guide [3], prestress [4], embedment in a solid matrix [5,6] … The aim of the thesis will be to develop an imaging method that takes into account both the difficulty of access to the structure (limited number of transducer positions) and the complex nature of guided wave propagation. Based on the theory of inverse problems in elastodynamics, the approach will consist in evaluating a gradient revealing the sensitivity of a cost functional to some parameters of the medium. The evaluation of this gradient in a healthy configuration (without defects) makes it possible to obtain, without iteration, a spatial representation of the defects present in the real structure. The gradient can be calculated very quickly (in "real time") thanks to the adjoint state method combined with the modal formalism of waveguides. At present, this approach has only rarely been applied to elastic waveguides [7]. Various questions remain open such as the influence of measurement and excitation configurations (frequencies, number of sensors and their placement, noise, etc.) and the choice of the gradient according to the type of defects. To answer these questions, the PhD student will use the modeling tools available in the laboratory to implement fast-imaging methods, test them on synthetic data, and finally on real data obtained from experiments. The PhD position will take place at the GeoEND laboratory (Geophysics and Non Destructive Evaluation) of Ifsttar, Nantes, France. The appointment will be for three years (beginning : October 2020, 1858€ gross per month for the first two years and 2165€ for the third year). Applicants should hold a MSc or equivalent in mechanics, acoustics, physics, applied mathematics or related fields, and have a strong background in numerical methods, finite element, waves or structural dynamics. Knowledge in inverse problems and signal processing would be appreciable. We are looking for excellent and highly motivated students. Please send a cover letter, official transcripts of the last two years, a CV with a brief statement of research experience along with the names and complete contact information of two references before April 3rd to: fabien.treyssede@ifsttar.fr and laurent.laguerre@ifsttar.fr https://www.ifsttar.fr/menu-haut/annuaire/fiche-personnelle/personne/treyssede-fabien/ https://www.ifsttar.fr/menu-haut/annuaire/fiche-personnelle/personne/laguerre-laurent/ Further details for the application process: https://www.ifsttar.fr/offres-theses/index.php References: [1] F. Treyssède, L. Laguerre, “Numerical and analytical calculations of the modal excitability for elastic wave generation in lossy waveguides”, Journal of the Acoustical Society of America 133, 3827-3837 (2013). [2] F. Benmeddour, F. Treyssède and L. Laguerre, “Numerical modeling of guided wave interaction with non-axisymmetric cracks in elastic cylinders”, International Journal of Solids and Structures 48, 764-774 (2011). [3] F. Treyssède, “Mode propagation in curved waveguides and scattering by inhomogeneities: application to the elastodynamics of helical structures”, Journal of the Acoustical Society of America 129, 1857-1868 (2011). [4]. F. Treyssède, A. Frikha and P. Cartraud, “Mechanical modeling of helical structures accounting for translational invariance. Part 2: Guided wave propagation under axial loads”, International Journal of Solids and Structures 50, 1383-1393 (2013). [5] K. L. Nguyen, F. Treyssède and C. Hazard, “Numerical modeling of three-dimensional open elastic waveguides combining semi-analytical finite element and perfectly matched layer methods”, Journal of Sound and Vibration 344, 158–178 (2015). [6] M. Gallezot, F. Treyssède, L. Laguerre, “A modal approach based on perfectly matched layers for the forced response of elastic open waveguides”, Journal of Computational Physics 356, 391-409 (2018). [7] S. Rodriguez, M. Deschamps, M. Castaings, and E. Ducasse, “Guided wave topological imaging of isotropic plates”, Ultrasonics 54, 1880-1890 (2014).
Keywords :	acoustic, wave, guide, mode, finite elements, modeling, simulation, imaging, experimental, inverse problem, adjoint state, time reversal

List of topics

Applications closed