Seminars

Coming seminars

Mar 25, 2021. 11:00 Vincent Richefeu
Professor 3S-R lab UGA  

Past seminars

Jan 21, 2021. 11:00 Dr Mohammad Rasool Mojallizadeh Postdoctoral research engineer in TriPOP team at INRIA Rhône-Alpes; LJK, UGA
  • topic : Time-discretizations of differentiators: design of implicit algorithms, and comparative analysis
  • Abstract : A complete review of the known differentiators and their time-discretizations have been addressed in this study. To solve the drawbacks of the explicit (forward Euler) discretization, which is commonly utilized in sliding-mode-based differentiators, implicit time discretization methods are proposed to handle the set-valued functions. The proposed schemes are supported by some analytical results to show their crucial properties, e.g., finite-time convergence, exactness, invariant sliding-surface, chattering elimination, insensitivity to the gains during the sliding-phase, and the well-posedness. The causal implementation of the proposed implicit schemes has been addressed clearly and supported by flowcharts. Semi-implicit schemes are also presented to provide a compromise between the performance and the ease of implementation. Finally, an exhaustive comparison is made using numerical simulations and practical experiments among 25 different state-of-the-art differentiators to evaluate the behaviors of the differentiators under different conditions. General conclusions are that implicit discretizations supersede explicit and semi-implicit ones.
  • The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
  • Slides : DIGIT_SLID_Final.pdf

Dec 10, 2020. 11:00 Dr Nicholas Collins-Craft
. TRIPOP team. INRIA
  • topic : Predicting strain localisation in crushable granular media using the Cosserat continuum
  • abstract: coming soonA consistent feature of the most destructive geological phenomena that humanity must live with, earthquakes and landslides, is the formation of thin bands featuring intense shearing that to a large extent control the global behaviour. While significant progress has been made in modelling these bands using the Cosserat continuum, existing models rely on a static mean grain size for their internal length scale. However, examination of shear bands in both the field and the laboratory reveals an extremely wide range of grain sizes due to the process of grain cataclasis, meaning that the modelling assumption of constant mean grain size is physically unjustifiable. In order to repair this defect, we first conducted some experiments to examine the effect of grain size polydispersity on shear band width. Then, using the results of these experiments and by coupling the Cosserat continuum with Breakage Mechanics, we obtained a model capable of predicting shear band formation in crushable granular media with an evolving grain size distribution. Finally, we examined the performance of this model in loading conditions analogous to the fast undrained shearing seen in earthquakes, and were able to explain the formation of “double shear bands” that are occasionally observed in the field.
  • info : The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
Dec 03, 2020. 11:00 Charlélie Bertrand. TRIPOP team. INRIA
  • topic : Dynamics of hauling rope : from curvilinear domains to its numerical computation
  • abstract : The presentation will be present a unified framework to compute the equilibrium of cable systems via Finite Element Methods. Starting from the equations of the curvilinear domains, it will be presented how the formulation of the problem has been adapted in order to account for noncompressibility of the media and the presence of obstacles with a particular interest for the practical case of a hauling rope (or telepheric installation).
  • info : The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
Nov 26, 2020. 11:00.  Dr Alexandre Rocca TRIPOP team. INRIA
  • topic : Nonsmooth methods for switching DAEs
  • abstract: In this work, we study how to apply methods from nonsmooth dynamics to ease the modelling and the simulation of multimode (also called hybrid) Differential Algebraic Equations (DAEs). This work is motivated by applications to the modelling energetic systems such as powerplants or energetic grids. In particular, we study how the nonsmooth dynamic formulations can be used to efficiently simulate multimode thermodynamic models such as such as the sevenequations models used by EDF to model phase changes. Such models are usually complex to simulate with the classical multimode approach. On a few examples, we show that our numerical methods can be used to simulate nonsmooth phase change models built from original EDF multimode models. We also show the current limitations of our approach and propose some guidelines to avoid them.
  • The seminar will held on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq

Nov 12, 2020. Dr Abhishek Chatterjee TRIPOP team. INRIA
  • topic : Modeling and simulation of multi-point collisions in rigid body systems
  • Abstract :This work presents a modeling and simulation technique for multi-point indeterminate (underdetermined) contact and impact problems in rigid body dynamic systems. Impacts between rigid bodies are characterized by discontinuous changes in velocities of the system, and therefore are modeled in impulse-domain. In the proposed framework impacts are treated as discrete events during which the velocities of the system evolve in the impulse-domain. Constraints derived based on the rigid body assumption are used to resolve indeterminacy associated with multi-point analysis. Also, a global energetic coefficient of restitution is proposed and used in this work, which characterizes the net energy loss through the system during impact, and guarantees energy consistency. One drawback of impulse-domain rigid impact models is that certain states such as deformation, contact force and time are ignored. This lost information can be useful for certain types of applications, where the contact force-history of an impact is of importance. Hence, the second part of this work presents an augmented rigid-impact model, which considers a contact force model from the contact mechanics literature along with the rigid impact model to also simultaneously determine the force and deformation histories during an impact event.
  • info : The seminar hold on big blue button app at https://webconf.gricad.cloud.math.cnrs.fr/b/vin-9ue-vqq
Jan 14, 2020. Pr Nicolas Moes. Ecole Centrale de Nantes, GeM, UMR CNRS 6183. Institut Universitaire de France
  • topic : Yet another way to solve LCP problems emanating from variational inequalities : the Inequality Level Set approach (ILS).
  • abstract:Variational inequalities when discretized in the usual way yield a linear complementarity problem (LCP). We discuss in the presentation a new approach in which the variational inequality is formulated in a different but equivalent way. The main unknown is the interface separating the active and inactive zones. By active we mean the domain over which the constraint is active. The equation governing the interface evolution is in general a variational equality (thus removing the need for a LCP solver).The approach is coined ILS for Inequality Level Set because a level set field is used to locate the interface. The ILS approach uses the mathematical tools of configurational mechanics since the interface is not material but immaterial in nature (configurational). Contact and bounded strain models are considered to demonstrate the capability of the ILS (see references).ReferencesGraveleau, M., Chevaugeon, N., & Moës, N. (2015). The inequality level-set approach to handle contact: membrane case. Advanced Modeling and Simulation in Engineering Sciences, 2(1), 16. https://doi.org/10.1186/s40323-015-0034-8Bonfils, N., Chevaugeon, N., & Moës, N. (2012). Treating volumetric inequality constraint in a continuum media with a coupled X-FEM/level-set strategy. Computer Methods in Applied Mechanics and Engineering, 205–208, 16–28 https://doi.org/10.1016/j.cma.2011.02.012
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 11:00
May 16, 2019. Dr Michael Brun, INSA-Lyon, Lyon, France
  • topic : Applications of subdomain coupling methods to structural dynamics and multiphysics
  • 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. First, subdomain coupling methods have been set up, following an energy-based argument, leading to the proposition of Hybrid Asynchronous Time Integrator (HATI), stable and second or first order accurate depending on the ratio between the time scales. A large variety of applications of the HATI is then presented in the fields of structural dynamics, soil-structure interaction (SSI) and fluid-structure interaction (FSI): reinforced concrete subjected to earthquake or blast loading, crane bridge under earthquake loading experiencing non smooth dynamics phenomena, wave propagation in unbounded soil domains by introducing Perfectly Matched Layers (PML), SSI problems by coupling seismology SEM (Spectral Element Method) code with a FEM code, FSI problems by coupling SPH (Smooth Particle Hydrodynamics) and FV (Finite Volumes) methods for the fluid with FEM code for the structure. The last application developed within LSMS laboratory, EPFL, concerns the simulation of an unbounded elastic block on a rigid flat plane, involving rate and state friction laws at the interface, compared to classical Coulomb’s law with constant friction coefficient.
  • Bio: Dr Michael BRUN is a teacher and researcher at INSA-Lyon, in civil engineering laboratory GEOMAS. His research interests focus on the computational science in dynamics, applied to civil engineering structures and multiphysics coupling problems such as soil-structure and fluid-structure interactions. He got his PhD at INSA-Lyon in 2002 and worked during three years as an engineer in a private company (EC2-Modélisation, Lyon) specialized in simulations and software development. Since 2005, he has joined INSA-Lyon where he holds the position of Associate Professor, teaching continuum mechanics, strength of materials and numerical methods in the civil engineering and urban planning Department of INSA-Lyon. He spent one year in LSMS laboratory, EPFL, as a visiting professor in 2018 to develop efficient coupling approaches for soil-structure interaction problems as well as algorithms for rate and state friction laws at the interface between sliding rock blocks.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 14:00
April 04, 2019. Rami Sayoud, INRIA, Schneider Electric
  • topic : Vibrations analysis of electrical switchboards
March 29, 2019. Hugo Parada, UTFSM, Chile and INRIA France
  • topic : Lur’e systems stability properties and numerical simulations
October 12, 2018. Mathias Legrand, McGill University, Canada.
  • topic : Nonsmooth modal analysis overview
  • abstract: Nonsmooth modal analysis aims at computing modeshapes and attendant frequencies of vibration of structural systems subject to unilateral contact constraints. Nonsmooth modes of vibration are defined as one-parameter continuous families of nonsmooth periodic orbits satisfying the local equation together with the linear and nonlinear boundary conditions. A one-dimensional rod system is considered for illustration purposes with various boundary conditions one of which being unilateral. Semi-discretization in space via traditional Finite Element formulations is known to induce difficulties in the formulation, notably in the form of an impact law which generates chattering. Instead, the analysis is performed using the wave finite element method which is a shock-capturing finite volume method. The spectrum of vibration shown in the form of backbone curves provides valuable insight on the dynamics. In contrast to the linear system whose modes of vibration are standing harmonic waves, the nonsmooth modes of vibrations are traveling waves stemming from the unilateral contact condition. It is also shown that the vibratory resonances of the periodically driven system with light structural damping are well predicted by nonsmooth modal analysis. Furthermore, the initially unstressed and prestressed configurations exhibit stiffening and softening behaviors, respectively, as expected. Possible extensions in multi- dimensional frameworks are suggested.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 14:00
October 11, 2018. Mathieu Rupin, Hap2U, France.
  • topic : A programmable haptic interface based on ultrasonic lubrication
  • abstract: Les interfaces tactiles – écran + capteur de position du doigt – se sont démocratisées, au point d’avoir investi tous les secteurs des interfaces homme-machine. Cependant, ces interfaces présentent un défaut majeur : on ne peut pas les utiliser sans regarder l’écran. Cela pose des problèmes de sécurité qui limitent encore leur déploiement (l’automobile en est le parfait exemple). hap2U a développé une technologie basée sur la mise en vibration, à des fréquences ultrasonores, de la surface de l’interface permettant de stimuler la pulpe du doigt de l’utilisateur et ainsi créer une sensation de texture (retour haptique). Le principe physique sur lequel repose cette technologie est la lévitation acoustique qui permet de modifier le coefficient de frottement du doigt. Afin de parvenir à proposer une expérience utilisateur de qualité, différents aspects technologiques jouent un rôle clé : minimisation de la latence du dispositif, adaptation d’impédance électromécanique, interfaces dédiées. Au cours de ce séminaire je vous proposerai un survol de notre activité couvrant les aspects physico-physiologiques et techniques ainsi que les enjeux économiques.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, G220, 14:00
October 04, 2018. Sami Karkar, Ecole Centrale Lyon
  • topic : Manlab : non linéarités et solutions périodiques, une approche numérique.
  • abstract: Manlab est, à la base, un outil numérique de continuation de solutions de systèmes d’équations algébriques quadratiques. Vers la fin des années 2000, au LMA (Marseille), cette méthode a été couplée à l’équilibrage harmonique, une méthode spectrale globale, qui permet de discrétiser la solution périodique d’un système dynamique par une somme de Fourier (tronquée). On montrera comment le couplage de ces deux méthodes, et par la suite l’utilisation de la collocation par polynômes orthogonaux, permet de résoudre une très grande variété de problèmes issus de la physique. On s’est intéressé en particulier à des modèles physique d’instruments de musique comportant des non-linéarités liées à un écoulement et à du contact non frottant, comme les instruments à anche simple (clarinette, saxophone). On s’est également intéressé à des problèmes de frottements (application au violon), non réguliers donc, mais par… régularisation.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 11:00

 

  • topic : Vers une méta-matière programmable.
  • abstract : Les métamatériaux sont des cristaux artificiels, c’est à dire des
    matériaux structurés, obtenus par la répétition d’une cellule
    élémentaire, sous forme de réseau, et faisant apparaître des propriétés
    exotiques (masse ou une densité négative par exemple), à des fréquences
    basses, c’est à dire des effets “sub-longueur d’onde”. On s’intéressera
    dans cet exposé plus particulièrement à des métamatériaux acoustiques
    “smart”, c’est à dire dont les propriétés sont ajustables, voire
    programmables, par l’intermédiaire de micro-capteurs et actionneurs
    intégrés. A partir de cette brique de base programmable, on
    s’intéressera alors au couplage entre une milieu classique de
    propagation acoustique, et une condition aux limites non standard, par
    exemple une équation différentielle, obtenue directement en
    “programmant” notre métamatériaux. On peut pour la suite penser à des
    problèmes d’optimisation de l’opérateur à programmer sur les frontières
    du domaine en fonction d’une “fonctionnalité” macro attendue… A terme,
    on pourra également programmer des effets non-linéaires, et donc
    potentiellement élargir encore un peu plus l’espace dans lequel
    effectuer ces optimisations.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, C207, 14:00

 

September 26, 2018. Félix Miranda. U. Cambridge
  • topic : Analysis of low-dimensional attractors in linear complementarity systems
  • abstract: Dissipativity theory is a powerful tool for the analysis of stability of equilibria in linear and nonlinear systems. In this work, we present an extension of the classical dissipativity framework that is useful for the analysis of low dimensional attractors in linear complementarity systems. Examples illustrate the proposed approach.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 10:00
September 20, 2018. Stéphane Grange and David Bertrand, INSA Lyon
  • topic : “Vulnérabilité physique des structures dans un contexte de risques naturels. Application aux chutes de blocs et aux séismes.”
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 10:00
July 19, 2018. Thoi Thi Tran, Université de Limoges
  • topic : Numerical optimization for contact problems.
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, F107, 10:00
July 4, 2018. Anindya Chatterjee from IIKT  (http://home.iitk.ac.in/~anindya)
June 28, 2018. Kirill Vorotnikov, TRIPOP Team
  • Topic :Application of numerical dissipation for the solution of multiple impacts problem in dissipative granular chains
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, C207, 11:00
March 29, 2018. Nicolas Molina Vergara, Pontificia Universidad Católica de Chile, Santiago, Chile.
  • Topic: “Alternating Direction Method of Multipliers (ADMM) for Frictional Contact”
  • info : INRIA Grenoble Rhone-Alpes, Montbonnot, C208, 11:00

 

 

 

 

 

 

 

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