On elastic open waveguides and their numerical modelling with a modal approach Matthieu Gallezot * 1,2

1 IFSTTAR, GERS, GeoEND, F-44344 Bouguenaix Cedex 2 Institut de Génie Civil et de Mécanique (GeM), Université de Nantes, UMR CNRS 6183, France Séminaire LaMé, Blois, 13 Décembre 2018

The practical concern of this talk is the non-destructive evaluation (NDE) with guided waves of elongated structures (bar, cables, pipes...) partially or totally embedded into a solid matrix (cement, rock...). These structures are widely encountered in civil engineering. Numerical models are used to obtain the properties of the waves modes (velocity, leakage attenuation...), which are essential to interpret the NDE results. This talk presents three numerical models recently developed to compute the dispersion curves, the forced response and the diffracted field in such structures.

These structures can be considered as elastic open waveguides, made of a core (the guiding structure) embedded into an infinite solid medium, such that the transverse directions (orthogonal to the direction of wave propagation) are unbounded. In this talk, a Perfectly Matched Layer (PML) of finite thickness is introduced to truncate the transverse directions. The cross-section of the waveguide can then be discretized with finite-elements while the direction of wave propagation is described analytically (SAFE-PML method). It yields a linear eigenvalue problem, which solution are the modes. Three types of modes are obtained: trapped modes, leaky modes and PML modes. The postprocessing of trapped modes and leaky modes enables to obtain the dispersion curves of the modes, of great practical interest. PML modes are non-intrinsic to the physics because they fully depend on the PML parameters. Examples of dispersion curves are shown for various waveguides geometries.

Then, the forced response and the diffraction problems are considered. An orthogonality relationship is derived to obtain the forced response with a unique modal superposition. Modal expansions can also be used to build transparent boundary conditions on the boundaries of a small finite-element volume enclosing a defect (hybrid method). It yields the reflection and transmission coefficients of leaky modes for any type of defect. Results are presented in various configurations for 2D and 3D waveguides damaged by a notch. A particular attention is given to the solution at high-frequency corresponding to a minimal * matthieu.gallezot@gmail.com 1 leakage attenuation, that is to a maximal inspection range for NDE.

Throughout this talk, the contribution of the various modes to the solutions is investigated. A mathematical study is used to clarify the effect of a PML on the modal spectrum of open waveguides. Numerically, it is shown that the solutions can be approximated in a restricted region of the waveguide by modal expansions on leaky modes only. This zone is delimited by the near-field of the source and the long-term diffraction limit. It enables to reduce the PML thickness and the number of computed modes, hence reducing the numerical cost.


Michael Kain

) -Information Analysis and Management (IAM) Provider of data storage and processing solutions for preclinical imaging studies Author

scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

by the national French action FLI-IAM (https://portal.fli-iam.irisa.fr). IAM (Information Analysis and Management) is the computation science node of France Life Imaging (FLI). It provides access to multiple imaging databases and computation resources and takes care of the interoperability between databases 1 and processing pipelines (local or cluster-based platforms). The preclinical work group within FLI-IAM has especially worked on a solution for hosting preclinical imaging studies, that is called Shanoir 2 Small Animal.

We will present the FLI-IAM architecture (fig. 1) and detail our Small Animal Shanoir (SAS) solution for hosting preclinical imaging studies (fig. 2, 3): data storage and processing execution and results integration via VIP 3 /Boutiques 4 .

Shanoir Small Animal provides:

• Control over the distribution and sharing of data

• Manages study meta-data and preclinical images using a specific ontology o Pathology models, therapies, anaesthetics and physiological data

• Import of Bruker and DICOM file formats (additional formats will be supported to comply with the evolution of the ecosystem)

• Secures online data sharing and data reuse

• Provides a storage of all research data in the cloud

• Original images + processing (code) + processed results

• Processes preclinical images on high performance systems, if required

• Support to integrate your data analysis pipeline and algorithms

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  Enriches data with links using DOIs to Open Access, e.g. OpenAIRE Currently FLI-IAM works on a new version of Shanoir called Shanoir-NG, with a completely new technological stack and architecture based on micro-services. We will detail the features of this new version and show how sharing of data and starting of pipelines work.

Figure 1 .Figure 2 .

 12 Figure 1. Architecture overview of FLI-IAM

Figure 3 .

 3 Figure 3. Shanoir-NG Small Animal, snapshot of an examination