Speaker: Marianne Conin
Date: Thursday 24th of April 2025, 1:15pm.
Abstract:
Coming soon
- Details
- Category: Seminar
Speaker: Yifan Xu
Date: Thursday 13th of February 2025, 1:15pm.
Abstract:
Variational gradient damage modeling, known nowadays as the variational phase field method, has been widely utilized in recent decades thanks to their efficiency in describing the transition from damage to fracture and predicting fracture nucleation and growth. In this work, we aim at proposing a phase field based Cohesive Zone Model (CZM) to simultaneously investigate the full coupling between gradient damage, poroelasticity and fluid flow phenomena in saturated porous media, as well as to well describe the damage zone that develops near the tip of quasi-brittle fractures. To this end, we mainly rely on the recent works of Zhang et al., 2024 (J. Mech. Phys. Solids, 187, 105614) and Wu, 2017 (J. Mech. Phys. Solids, 103, 72-99) in order to incorporate the cohesive zone effect in the corresponding incremental variational formulation of this fully coupled system. The proposed incremental variational approach consists in the minimization of a three-field incremental energy functional, which depends on the displacement and damage fields of the skeleton phase of the porous media as well as the pore fluid pressure. For numerical implementation, we adopt a semi-staggered optimization algorithm by making use of FEniCS platform and apply it to simulations of the KGD fracture problem and hydraulic fracturing problems involving multiple cracks for which corresponding analytical solution and/or numerical results are available. Taking advantage of this framework, this is finally applied to assess the feasibility and stability of an industrial radioactive waste repository in the Callovo-Oxfordian (COx) claystone formation, where the host rock presents significant cohesive characteristics. The numerical results are compared with the in-situ observations. Reliable predictions such as the extension of the excavation-induced damaged zone (EDZ) as well as pore pressure distribution are provided.
- Details
- Category: Seminar
Speaker: Loïs Letellier
Date: Thursday 10th of April 2025, 1:15pm.
Abstract:
Well log interpretation is a time consuming task, which, moreover, depends on the interpreter's experience, as there exists different admissible interpretations for a same input log. To account for the uncertainty of the interpretation, we propose to use a signal processing technique, the Continuous Wavelet Transform (CWT), that gives information on the signal considering both depth and scale parameters. The result of this transform is then processed to extract some features of the signal (i.e. the local extrema of the signal at different scales), and propose different geological scenarios. We then compare the different solutions with experts' interpretations.
These different scenarios are destined to be included in a correlation process, in order to study correlations with a multi-scale approach, which allows to explore the range of possibilities, while reducing the computational cost using a hierarchical process.
- Details
- Category: Seminar
Speaker: Léo Letellier
Date: Thursday 06th of February 2025, 1:15pm.
Abstract:
To Rust or not to Rust, that is the question in today's choice of programming languages. While hunting for bugs and security vulnerabilities is a principal concern in software development, memory safety is found to be involved in a majority of such cases (70% of all vulnerabilities reported by a Microsoft engineer in 2019). Multiple tools and enhancements are proposed to mitigate this risk. The Rust programming language was developed to answer this problem in a more controlled way, providing systematic memory safety while preserving performance. It is particularly fit for usage in CLI (Command Line Interface), networking, and embedded devices. It also targets WebAssembly, making code web-ready with minimal changes. Considering these features, multiple agencies such as the NSA emphasize the need to use memory-safe languages such as Rust. Rust was also determined to be the most admired language for multiple years in a row by the developer survey of Stackoverflow (83% in 2024), and is ranked 14 in the January 2025 Tiobe index.
- Details
- Category: Seminar
Speaker: Mike Heap
Date: Thursday 27th of March 2025, 1:15pm.
Abstract:
Hydrothermal alteration describes a process that progressively, and additively, modifies the chemical, physical, mechanical, and transport properties of rock by fluid-rock interactions. At active volcanoes, mixtures of magmatic and meteoric fluids circulate within the rocks forming the volcano and, as a result, hydrothermal alteration can be pervasive. Because the properties of volcanic rocks and rock-masses, such as their strength or their permeability, play a role in dictating the hazard potential of a volcano, then it follows that hydrothermal alteration can progressively modify the hazard potential of a volcano. However, not only does subsurface hydrothermal alteration proceed largely imperceptibly, leading to unpredictable hydrothermal explosions and mass wasting events, but we also do not fully understand the timescales required for hydrothermal alteration, nor its influence of rock properties. As a result, and despite its potential importance, hydrothermal alteration is not routinely monitored at active volcanoes, and often does not feature in routine volcanic hazard assessments. In this seminar, I will outline recent, multidisciplinary advancements in our understanding of hydrothermal alteration, and its influence on volcanic hazards.
- Details
- Category: Seminar
Speaker: Mariam Joundi
Date: Thursday 30th of January 2025, 1:15pm.
Abstract:
Dans le contexte de l'ambition climatique de l'Union Européenne visant la neutralité carbone à l'horizon 2050, l'hydrogène vert émerge comme un vecteur énergétique prometteur. Cette orientation stratégique nécessite l'élaboration de solutions innovantes pour le transport sécurisé de l'hydrogène (European Hydrogen Backbone, 2020). En France, une réorientation des infrastructures est envisagée, avec la proposition de réutiliser les réseaux de gaz existants pour le transport de l'hydrogène (GRTgaz, 2019). Cependant, cette substitution induit des modifications significatives des caractéristiques mécaniques des réseaux, augmentant ainsi leur vulnérabilité vis-à-vis les sollicitations externes (Boots et al., 2021). Dans le cadre d'une thèse, nous explorons l'interaction entre ces réseaux et les mouvements de terrain, dans le but de minimiser les risques associés.
Dans ce contexte, cette étude vise à développer un méta-modèle basé sur une modélisation numérique tridimensionnelle pour évaluer l'impact des affaissements de terrain sur les réseaux de gaz enterrés. Le méta-modèle développé cherche à quantifier le taux de transmission des affaissements de sol aux conduites, en fonction d’un coefficient de rigidité relative sol-conduite. Ce travail s'inscrit dans une démarche novatrice par son approche tridimensionnelle, offrant une perspective plus complète par rapport aux méta-modèles similaires développés dans la littérature, se reposant sur des modèles de base analytiques ou numériques (Joundi et al., 2023).
Une analyse numérique paramétrique, intégrant un total de 230 simulations par éléments finis (EF), a été développée, aboutissant à l'élaboration d'un premier méta-modèle. Ce méta-modèle établit une relation entre la courbure relative des pipelines et un coefficient de rigidité relative du système sol-pipeline, constituant ainsi une base robuste pour des évaluations probabilistes futures. Ce modèle a été comparé au méta-modèle de Wang et al. 2011 afin de positionner nos résultats dans le contexte des recherches existantes.
Des premières simulations de propagation d’incertitudes ont été menées pour évaluer la probabilité de défaillance des conduites exposées à un affaissement, aboutissant à l’établissement de premières courbes de vulnérabilité.
- Details
- Category: Seminar
Speaker: Michael Brun
Date: Friday 17th of January 2025, 1:15pm.
Abstract:
The increasing complexity of numerical models for engineering systems, taking into account ever finer mesh, accurate material models and multiphysics phenomena, occurring at very different space and time scales, boosted the development of partitioning approaches. In the field of structural dynamics, the main advantage of partitioning approaches is to gain in computational efficiency by using different time integrators with their own time step, depending on the non-overlapping subdomains composing the global mesh. It leads to the proposition of Hybrid Asynchronous Time Integrator (HATI). A large variety of HATI applications is then presented in the fields of structural dynamics and earthquake engineering, including smooth dynamics without contact as well as non-smooth dynamics with frictional contact phenomena.
First, HATI is employed for Reinforced Concrete structures under earthquake loading, without contact, using multi-fibre beam elements whose cross-section is divided into steel and concrete fibres associated with cyclic and nonlinear behaviors. Then, the frictional contact is explored by developing an explicit time integrator in Moreau’s framework, called CD-Lagrange scheme, based on the velocity-impulse formulation with the contact constraints enforced using Lagrange multipliers. The CD-Lagrange scheme is adopted for reproducing the frictional contact phenomena experiencing by crane bridge under earthquake loading following the HATI approach. It enables us to focus on high frequency phenomena with frictional contacts in small subdomains including the rails of the girder beams and the trolley wheels, using small time steps satisfying the CFL condition, whereas the main part of the complex problem is dealt with a classical implicit time integration scheme with large time steps. In this way, we benefit from advantages of the two time integrators, leading to computation time gains as well as versatility in applying appropriate damping formulations depending on explicit or implicit subdomains. CD-Lagrange scheme is also adopted for simulating the eccentric pounding phenomena between real scale two-storey steel-concrete structures, tested on the shaking table AZALEE (CEA Saclay, France), enabling us to obtain very satisfactory results with respect to experimental data, in terms of floor displacements and acceleration spectra in a large frequency range.
Soil Structure Interaction (SSI) problems are also considered by developing Multi Time Step Hybrid Perfectly Matched Layers (PML) in the context of the simulation of wave propagation in the time domain for 2D and 3D unbounded domains. Indeed, HATI approach is useful to integrate in time the complex space semi-discrete equations in the 2D/3D PMLs, independently from the time integration of the classical semi-discrete equations of motion in the domain of interest. Hybrid PMLs are also employed in research developed within LSMS laboratory, EPFL, concerning the simulation of an unbounded elastic block on a rigid flat plane: It involves rate and state friction laws at the interface, compared to classical Coulomb’s law with constant friction coefficient.
On the basis of the HATI approach, multi time step explicit/implicit co-simulation strategies are developed in order to couple a seismology software (EFISPEC3D, BRGM) based on 3D Hexahedral Spectral Elements with FE software (Akantu, EPFL) in the context of SSI applications: A seismic non-linear analysis of a concrete gravity dam is carried out using the HATI approach combined with mortar coupling to deal with non-matching meshes at the interface between the subdomains. The seismology software simulates the seismic source as well as the large medium concerned by the wave propagation, using an explicit time integrator, whereas the non-linear behavior of the dam is simulated by the FE software with an implicit time integrator.
To conclude, the presented works aim at developing numerical coupling approaches in order to tackle complex problems in structural dynamics. The conducted research has deep roots in Computational Mechanics while focusing on Earthquake Engineering problems in a constant effort to apply the developed innovative tools to engineering systems.
- Details
- Category: Seminar
Speaker: Bastien Morin
Date: Thursday 27th of February 2025, 1:15pm.
Abstract:
Les réservoirs miniers, formés par l’ennoyage des travaux après l’arrêt de l’exploitation du charbon, sont le siège de processus géochimiques complexes. Dans la mine de lignite de Gardanne, la roche exploitée se mêle à des formations calcaires, entraînant des interactions eau-roche spécifiques qui influencent les équilibres géochimiques. Les concentrations en fer, issues du drainage minier neutre, y posent d’importants défis environnementaux. Cette présentation décrit la campagne de terrain menée au puits Gérard à Mimet fin octobre 2024 dans le cadre de mes travaux de thèse. Au cours de cette campagne, des mesures physico-chimiques détaillées ont été réalisées, accompagnées de prélèvements d’eau à différentes profondeurs, suivis d’analyses chimiques, isotopiques et microbiologiques.
- Details
- Category: Seminar