ESPCI web site
Séminaire café 2023
| 5 jan | Galette des Rois |
| 12 jan | TBA |
| 26 jan | Mehdi Bouzid Chargé de recherche à Univ. Grenoble Alpes Post PhD’s adventure trails |
| 2 févr | Juan D’Adamo Researcher at CONICET, Argentina Wake and aeroelasticity of a flexible pitching foil A flexible foil undergoing pitching oscillations is studied experimentally in a wind tunnel with different imposed free stream velocities. The chord-based Reynolds number is in the range 1600–4000, such that the dynamics of the system is governed by inertial forces and the wake behind the foil exhibits the reverse Bénard–von Kármán vortex street characteristic of flapping-based propulsion. Particle image velocimetry (PIV) measurements are performed to examine the flow around the foil, whilst the deformation of the foil is also tracked. The first natural frequency of vibration of the foil is within the range of flapping frequencies explored, determining a strongly-coupled dynamics between the elastic foil deformation and the vortex shedding. Cluster-based reduced order modelling is applied on the PIV data in order to identify the coherent flow structures. Analysing the foil kinematics and using a control-volume calculation of the average drag forces from the corresponding velocity fields, we determine the optimal flapping configurations for thrust generation. We show that propulsive force peaks occur at dimensionless frequencies shifted with respect to the elastic resonances that are marked by maximum trailing edge oscillation amplitudes. The thrust peaks are better explained by a wake resonance, which we examine using the tools of classic hydrodynamic stability on the mean propulsive jet profiles. |
| 9 févr | Jonathan Lalieu Doctorant au FAST (Université Paris-Saclay/CNRS) Non-local rheology of a 2D particle-laden soap film |
| 16 févr | Pas de réunion café |
| 23 févr | Christine Ozouf Responsable accueil et mobilité des chercheurs et étudiants à l’international, SU Accueillir un chercheur étranger |
| 2 mars | TBA |
| 9 mars | TBA |
| 16 mars | Alice Pelosse Doctorante au MSC Blood, paint, cement, mudslides or avalanches are suspensions, mixtures of particles suspended in a fluid. When the Brownian motion of the particles is negligible, we speak more specifically of granular suspensions, complex fluids that present surprisingly simple volume properties with a continuous medium approach. As an example, for a concentrated monodisperse suspension with a solid fraction ϕ of 40%, the mixture remains Newtonian and its effective viscosity is 10 times that of the suspending fluid, whatever the particle size. This seminar focuses on concentrated granular suspensions with free interfaces and more particularly on the spreading of a drop [1]. The volume properties of the continuous medium approach are challenged by a moving interface that has to deal with the biphasic flow. In the vicinity of the contact line, the particles cannot approach because of their size. The size of the pure fluid zone increases with the diameter of the particles. When the thickness is sufficient, a highly ordered monolayer is observed, a consequence of the extreme confinement of the particles. Further away follows a disordered region when the confinement by the interface becomes less important. Through an experimental and theoretical approach, the influence of the particles on the dynamical wetting is studied. The classical models (Cox-Voinov, Tanner) remain valid with effective viscosities. However, contrary to the volume properties, the effective viscosity of a wetting suspension is strongly affected by the particle size. In particular, for particles larger than 100 microns, the measured viscosity is that of the pure fluid. This characteristic size of viscous "cut-off" is found thanks to the analysis of the spreading equations and confirmed experimentally. The study of bidisperse systems confirms the effects of size and order of the particles near a contact line in advance. Finally, the global spreading dynamics is studied and related to local observations near the contact line. [1] A. Pelosse & E. Guazzelli & M. Roché, Probing dissipation in spreading drops with granular suspensions, Journal of Fluid Mechanics, 954, A7 (2023). |
| 23 mars | Pas de séminaire café (grève) {} |
| 30 mars | Pas de séminaire café (RNL) {} |
| 06 avril | Louis Galiègue Stagiaire au MecaWet The subject of interest of this internship was the study trough numerical simulation of the propagation of cracks which can appear in tires. This phenomenon starts by a disadhesion between the cable and the rubber in composite plies where the metallic cords are used as reinforcements to the rubber matrix. As the adhesion is no longer ensured, a crack is initiated and can subsequently propagate. The goal for endurance is to know how to anticipate the different parameters of the propagation : its direction, its speed, but also where it will end up. Being able to predict how a change in architecture, material or operating conditions will influence the propagation of these defects is a key issue. For this, two approaches are used : a multi-scale finite-element approach in the case of the tire, and a simplified approach on a specimen modeling the cable-rubber bond. Both approaches use ZCRACKS, a module for 3D fracture mechanics simulation developed with ONERA and Mines de Paris which allows for cracks insertion, 3D energy restitution rate calculation and iterative crack propagation. |
| 13 avril | Pas de séminaire café (soutenance de thèse de Magda) |
| 20 avril | Daniel Korchinski PhD student at University of British Columbia, Vancouver, Canada Temperatures and criticality in amorphous solids Amorphous solids are a disparate class of materials, including glasses, foams, emulsions, and granular packings. Surprisingly, they exhibit some shared universal behaviour in their mechanical response to load, with an initially elastic regime giving way to a jerkily flowing state characterized by intermittent bursts of activity dubbed ``avalanches’’. This driven state is a dynamical phase transition, exhibiting avalanches and rheological behaviour characterized by nontrivial critical exponents. Although this example of self-organized criticality has been extensively studied in the zero-temperature limit, comparatively little work studies the effects of temperature on the self-organized criticality of this system. In this talk, I will discuss how temperature, driving rate, and finite-size effects compete to truncate avalanches and tune the system away from criticality. Using a mesoscale model of amorphous plasticity equipped with a temperature dependent activation of weak-sites, we derive a phase-diagram for the critical behaviour and various scaling results in temperature and finite-size truncated phases [1]. In the continuously flowing state, when avalanches overlap, we also find a change in the flow exponents at high temperature, which we will compare to data obtained at other scales. [1] D. Korchinski and J. Rottler, Dynamic Phase Diagram of Plastically Deformed Amorphous Solids at Finite Temperature, Phys. Rev. E 106, 034103 (2022). |
| 27 avril | Thomas Alline Doctorant au MSC Mechanobiology of the root hair cell Plant growth is controlled by genetic circuits but also by mechanical cues as the plants need to adapt to their mechanical environment. The plant roots are good systems to study such an adaptation since they grow in soils with many mechanical heterogeneities. Our aim is to understand the mecanotransduction from the cell wall to the nucleus in growing plant roots. In particular, we study the growth of the root hair cell which is a single cell, from the root epidermis, exhibiting tip growth. Combining microfluidics and optical microscopy, we quantitatively characterize the growth of single root hairs by measuring, in different conditions and mechanical environments, their growth speed and the concomitant nuclear dynamics. In particular, using growth media of increasing young moduli leads to root hairs with decreasing growth speed and length, whereas growth duration is unaffected. Interestingly, the stiffness of the growth medium also affects nuclear dynamics, suggesting mechanotransduction from the root hair cell surface to the nucleus. We then want to better understand the effect of mechanical cues on root hair growth by controlling the force exerted on the root hair tip and the rigidity detected by the root hair cell using a glass microplate technique. |
| 4 mai | Pas de séminaire café (visite du MSC) |
| 11 mai | Stéphane et Baptiste Retour de mission du Canada |
| 18 mai | Ferié - Jeudi de l’Ascension |
| 25 mai | Valentin Mouet Doctorant au LPENS Water waves control by electrostriction : principles, wave propagation in space and time-varying media The control of wave propagation based on refraction principles offers unparalleled possibilities as shown by the striking example of optics. This approach is unfortunately limited for water waves as it relies mainly on variations of the liquid depth which, while controlling the wave velocity, also trigger nonlinearities and damping. In this seminar, I will present the basic principles of water waves control using electrostriction and I will show that electrostriction allows to implement extensive refraction-based control of water waves in a precise and contactless manner. Although these examples are based on space-varying propagation properties, it is actually easy to change those properties in time. I will conclude with some examples where propagation properties are both space and time-varying and lead to unusual situations. |
| 1 juin | TBA |
| 8 juin | Pas de séminaire café - Xavier PhD defense |
| 15 juin | Pas de séminaire café - Lars PhD defense |
| 22 juin | Sylvain Patinet, Philppe Claudin, Etienne Reyssat, Anne Mongruel, Baptiste Auvity, Benoit Roman Bilan carbone du laboratoire |
| 29 juin | Sameh Tawfick University of Illinois Urbana Champaign Polymorphic Texture Integrated Systems (Polytexis) via Hydrodynamic Elastocapillarity My group recently demonstrated that hair and fins self-assemble into polymorphic patterns due to the combination of capillary effects and hydrodynamics. In this Coffee Talk, I will share our recent work on exploiting these phenomena to produce polymorphic texture integrated systems (polytexsis). Polytexis are soft-fin devices controlled by fluidic flow for reflective display, camouflage, and texture modulation. Short Biography Sameh Tawfick is a Visiting Professor in the University of Cambridge and a Beaufort Visiting Fellow in St John’s College. Prof. Tawfick’s home institution is the University of Illinois Urbana-Champaign where he is currently an Associate Professor of Mechanical Science and Engineering, having received the Dean’s Award for Excellence in Research. Sam obtained his PhD from the University of Michigan and was a Postdoctoral Associate at the Massachusetts Institute of Technology. He studies advanced materials, nonlinear mechanics, and manufacturing processes. |
| 6 juillet | Chloé Lindeman Physics Departement, University of Chicago Motion of driven and relaxing contact lines A liquid drop moving across a solid surface involves subtle and complex phenomena, particularly at the contact line where liquid, solid, and air all meet. One route to describing drop motion has been to borrow ideas from friction, another process with complex microscopic details yet robust macroscopic phenomena. Here, we study the contact line motion of water drops as they are withdrawn from surfaces with moderate contact angle hysteresis. I will show that the behavior is well described by overdamped (drag-dominated) dynamics, with an unexpected control parameter that can be quantified by fitting for the damping coefficient. By turning off the flow mid-experiment, we can also observe contact line relaxation toward an equilibrium contact angle, providing additional insight into details of the damping behavior and suggesting that damping decreases with contact line velocity. |
| 31 août | Marie Tani |
| 7 septembre | Pas de séminaire café - conseil du labo |
