Seminars

9th seminar of Team CaliSto

  • Date & Time:
    Friday, July 2nd, 2021 at 10:00 (CET)
  • Speaker:
    1) Mickael Binois (researcher in Team Acumes, Inria Sophia Antipolis)
    2) Areski Cousin (professor at IRMA Université de Strasbourg, and associate researcher in Team Calisto)
  • Topic:
    Two presentations on:
    1) Analysis of complex simulation experiments with Gaussian processes
    2) Beyond Surrogate Modeling: Learning the Local Volatility via Shape Constraints
  • Abstract:
     – 1st presentation:

    We present an overview of the use of Gaussian processes as surrogate models for expensive-to-evaluate black-boxes. In particular, we focus on calibration (inverse problem) and uncertainty quantification, illustrated by several application examples from various domains.
    – 2nd presentation:
    We explore the abilities of two machine learning approaches for no-arbitrage interpolation of European vanilla option prices, which jointly yield the corresponding local volatility surface: a finite dimensional Gaussian process (GP) regression approach under no-arbitrage constraints based on prices, and a neural net (NN) approach with penalization of arbitrages based on implied volatilities. This presentation will focus on the GP approach. We demonstrate the performance of these approaches relative to the SSVI industry standard. The GP approach is proven arbitrage-free, whereas arbitrages are only penalized under the SSVI and NN approaches. The GP approach obtains the best out-of-sample calibration error and provides uncertainty quantification, which is useful for the assessment of model risk. The NN approach yields a smoother local volatility and a better backtesting performance, as its training criterion incorporates a local volatility regularization term.
    Link to the presentation: PDF 1, PDF 2

8th seminar of Team CaliSto

  • Date & Time:
    Thursday, June 3rd, 2021 at 10:00 (CET)
  • Speaker:
    Rudy Valette (professor in Team CFL at CEMEF Mines-ParisTech, Sophia Antipolis, France)
  • Topic:
    Modeling and numerical simulations of fluid flows with complex rheology
  • Abstract:
    Heterogeneous fluids (pastes, granular, suspensions, emulsions…) generally present a strongly non-Newtonian rheology. They flow very differently from fluids such as air, water or honey. We will show various examples of flows (stretching or compression of filaments, jets, collapses, extrusion…) showing instabilities related to their rheology and discuss with the help of experiments, numerical simulations and simple theoretical analysis the mechanisms involved in these flows. Several examples will be proposed and the interest of numerical simulation will be underlined, both for the understanding of simple phenomena, but also for the prediction of more complex flows, such as those encountered in industry or in nature.
  • Link to the presentation: TBA

7th seminar of Team CaliSto

  • Date & Time:
    Thursday, May 6th, 2021 at 10:00 (CET)
  • Speaker:
    Agnese Seminara (CNRS researcher at Institut de Physique de Nice, France)
  • Topic:
    Sensory navigation using turbulent odor cues
  • Abstract:
    Organisms use a variety of sensory cues to navigate to targets like food or mates, and to escape predators. Chemical and mechanical signals are carried long distance by fluid flows, but at the same time they are often distorted and broken in intermittent patches by turbulence. Here we draw inspiration from olfactory navigation in octopuses and mice and ask how can organisms predict the location of a target, using its turbulent odor cues. I’ll show how tracking odor cues for few seconds is sufficient to make predictions, if care is taken into quantifying both intensity and timing of odor detections. I’ll map our predictions on our preliminary data of odor representation in the mouse brain.
  • Link to the presentation: TBA

6th seminar of Team CaliSto

  • Date & Time:
    Thursday, April 8th, 2021 at 10:00 (CET)
  • Speakers:
    Jérôme Yon (researcher at Dept. Optic & Laser, CORIA, Rouen, France)
    et José Moran (PhD student at Dept. Optic & Laser, CORIA, Rouen, France)
  • Topic:
    Simulation of the formation of soot particles: toward a better characterisation of these particles.
  • Abstract:
    Soot particles are formed due to the incomplete combustion of flames. These particles are not spherical and display a range of fractal morphologies that have to be take into account in various situations (metrology, transport, deposition, …). Tools based on laser metrology are being developed at CORIA to characterize such particles with in-situ measurements. A precise characterisation requires to accout for the fractal morphology of aggregates. To that extent, a code has been developed (called MCAC, for Monte Carlo Aggregation Code) to compute realistic soot aggregates. In this seminar, we will present the issues related to the characterisations of such particles using optical techniques as well as the principle of MCAC. Recent results obtained with this code will also be presented.
  • Link to the presentation: PDF

5th seminar of Team CaliSto

  • Date & Time:
    Thursday, March 11th, 2021 at 10:00 (CET)
  • Speakers:
    Grégory Lécrivain (researcher at the Institute of Fluid Dynamics, HZDR, Germany)
    and Christophe Henry (researcher at Team CaliSto, Inria Sophia-Antipolis, France)
  • Topic:
    Particle resuspension from monolayered deposits: evidence of collision-induced phenomenon
  • Abstract:
    We present here new experimental and numerical results for the resuspension of microscopic glass particles from a monolayer bed into a turbulent gas flow. With an intermediate surface coverage, here about 10 % of the field of view, we report two distinct detachment mechanisms: collision-induced resuspension at low flow velocities and individual particle resuspension at higher fluid velocities.
  • Link to the presentation: TBA

4th seminar of Team CaliSto

  • Date & Time:
    Thursday, February 11th, 2021 at 10:00 (CET)
  • Speaker:
    Florence Marcotte (researcher at Team Castor, Inria Sophia-Antipolis, France)
  • Topic:
    Corrola from drop impacts on viscous fluids
  • Abstract:
    L’étude des substrats de viscosité variable est motivée par la volonté de réconcilier d’abondantes observations d’impacts de gouttes, qui dans la littérature mettent en évidence des dynamiques de splash très diverses, d’une part pour les impacts sur substrat solide, d’autre part pour les impacts sur substrat liquide. Faire varier la viscosité du substrat sur plusieurs ordres de grandeur permet de capturer la transition d’un régime de splash-sur-liquide à celui de splash-sur-solide, et de clarifier le rôle du substrat dans la formation de la corolle d’impact.
  • Link to the presentation: PDF

3rd seminar of Team CaliSto

  • Date & Time:
    Thursday, January 14th, 2021 at 10:00 (CET)
  • Speaker:
    Aurore Dupré (post-doc at Team Calisto, Inria Sophia-Antipolis, France)
  • Topic:
    Uncertainty quantification in CFD simulations of multiphase flow
  • Abstract:
    In this work, we present recent advances that have been made within the framework of the VIMMP project (Virtual Materials Market Place). We start by introducing the workflow studied (including both the physical aspects, the modelling approaches retained and the numerical tools used). Sensitivity analysis tools are then presented and used to identify the key parameters affecting the observed results.
  • Link to the presentation: PDF

2nd seminar of Team CaliSto

  • Date & Time:
    Thursday, December 10th, 2020 at 10:00 (CET)
  • Speaker:
    Luca Berti (PhD at IRMA, Strasbourg, France)
  • Topic:
    Developments in Feel++ for micro-swimming simulations
  • Abstract:
    In this talk, we will focus on the additions and developments motivated by micro-swimming simulations in the Feel++ library. We will talk about articulated swimmers, remeshing and the interfacing of fluid and elasticity equations for a moving body.
  • Link to the presentation: PDF

1st seminar of Team CaliSto

  • Date & Time:
    Thursday, November 5th, 2020 at 10:00 (CET)
  • Speaker:
    Kerlyns Martinez-Rodriguez (post-doc at Team Calisto, Inria Sophia-Antipolis, France)
  • Topic:
    Physical-based probabilistic models for the instantaneous turbulent kinetic energy:modelling, calibration and validation
  • Abstract:
    In this talk, we present the construction of a probabilistic model for the instantaneous turbulent kinetic energy filtered at a given point in space. For this, we start from the Lagrangian description of fluid flow and derive a mean-field dynamic featuring the square norm of the turbulent velocity of a generic fluid particle. By approximating at equilibrium the nonlinear terms, we recover the CIR-form previously suggested in the literature for modelling the wind speed. In a second part, we establish a calibration procedure for the parameters by employing classical explicit methods and Bayesian inference. In particular, we show the consistency of the estimators and validate the model through the quantification of uncertainty.
  • Link to the presentation: PDF

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