PhD defense on October 18th, 2018, 2:30pm, at the PMMH meeting room (Sorbonne Université, Barre Cassan, Bât. A 1er Étage, 7 Quai Saint Bernard, 75005 Paris).
Acoustic confinement of Escherichia coli: The impact on biofilm formation
Brownian or self-propelled particles in aqueous suspensions can be trapped by acoustic fields generated by piezoelectric transducers usually at frequencies in the Megahertz. The obtained confinement allows the study of rich collective behaviours like clustering or spreading dynamics in microgravity-like conditions. The acoustic field induces the levitation of self-propelled particles and provides secondary lateral forces to capture them at nodal planes. Here, we give a step forward in the field Continue reading “PhD defense: Salomé Gutiérrez-Ramos. Acoustic confinement of Escherichia coli: The impact on biofilm formation”
PhD defense on October 1st, 2018, 2:30pm, at the PMMH meeting room (Sorbonne Université, Barre Cassan, Bât. A 1er Étage, 7 Quai Saint Bernard, 75005 Paris).
Converting wave energy from fluid–elasticity interactions
Understanding the mechanisms involved in wave-structure interactions is of high interest for the development of efficient wave energy harvesters as well as for coastal management. In this thesis, we study the interactions of surface waves with a model array of slender flexible structures, in view of developing an efficient system for both attenuating and harvesting wave energy. The presented results are based around experimental investigations, by means of small scale facilities, in which the spatial arrangement of the flexible objects is the key parameter of Continue reading “Clotilde Nové-Josserand’s PhD defense. Converting wave energy from fluid–elasticity interactions”
PhD defense on April 4th, 2018, 3pm, at the new PMMH meeting room (Sorbonne Université, Barre Cassan, Bât. A 1er Étage, 7 Quai Saint Bernard, 75005 Paris).
Interactions in Collective Fish Swimming
The question of how individuals in a population organise when living in groups arises for systems as different as a swarm of microorganisms or a flock of seagulls; and the different patterns for moving collectively involve a complex interaction of a wide spectrum of reasons, such as evading predators, optimising food prospection or diminishing energy consumption. The basic ingredient in such problems is the communication mechanism between individuals, that is to say, the way in which two neighbours sense each other, constituting the fabric of social behaviour. In this work we studied the case of fish schooling using a popular aquarium fish, the red nose tetra fish Hemigrammus bleheri. These fish are known to swim in highly cohesive groups and to sense each other both visually and through the lateral line, a system of organs based on the ability of hair cells to detect movement in their environment. In our experiments Continue reading “Intesaaf Ashraf’s PhD defense. Interactions in Collective Fish Swimming”
PhD defense on November 10th, at 2pm, in the auditorium of the Grande Galerie de l’Evolution.
Water as a driver of evolution: the example of aquatic snakes
1. UMR 7179, CNRS-MNHN, Mécanismes adaptatifs et Evolution, équipe FUNEVOL, Département d’Ecologie et de Gestion de la Biodiversité. Pavillon d’anatomie comparée, 55 rue Buffon, case postale 55, 75231 Paris cedex 5, France.
2. UMR 7636, CNRS, ESPCI Paris–PSL Research University, Sorbonne Université, U Paris Diderot, Physique et Mécanique des Milieux Hétérogènes. 10 rue Vauquelin, 75005 Paris, France
Animal-environment interactions are determinant in driving the evolution of phenotypic variation. Most aquatic animals have developed adaptations to overcome the physical constraints inherent to an aquatic lifestyle and particularly to motion in water. These constraints are the drag and the added mass if an acceleration is involved in the motion, such as during prey capture. The aim of this project is to evaluate the role of water as a potential driver of evolution of aquatic snakes by focusing on morphological and behavioral convergences during underwater prey capture. Snakes are a good model as an aquatic life- Continue reading “Marion Segall’s PhD defense. Water as a driver of evolution: the example of aquatic snakes”
PhD defense on January 10, 2014 at ESPCI
Propulsion biomimétique de structures élastiques
Birds and aquatic animals exploit the surrounding fluid to propel themselves in air or water. In inertial regimes, the mechanisms of propulsion are based on momentum transfer; by flapping wings or fins, animals accelerate fluid in their wake, creating a jet that propels them forward. The structures used to move can be flexible, and are thus likely to experiment large bending. Literature showed that those passive deformations can improve propulsive performance, when exploited in a constructive way. The mechanisms at play however remain poorly understood. In the present thesis, we aim at studying how a flapping elastic structure generates thrust, using two experimental biomimetic models. The first setup is a simplified mechanical insect with flexible wings, and the second one is a swimmer whose elastic body mimics the undulating motion of an eel. We show that propulsive performance is significantly influenced by the way the systems passively bend, and that their elastic response can be described by simplified theoretical models of forced oscillators. Those models also bring forward the crucial role of the quadratic fluid damping that resists the flapping motion. This result introduces the counter-intuitive idea that it is sometimes desirable to dissipate part of the energy in the fluid, in order to improve performance.
Christophe Clanet (Rapporteur)
Christophe Eloy (Rapporteur)
Yves Couder (Président)
Emmanuel de Langre (Examinateur)
Jean-Marc Di Meglio (Examinateur)
Ramiro Godoy-Diana (Directeur de Thèse)
Benjamin Thiria (Directeur de Thèse)
PhD defense on January 14th, 2011 at Amphi Langevin, ESPCI
Dynamique tourbillonnaire dans le sillage d’un aileron oscillant: Propulsion par ailes battantes biomimétiques
This thesis deals with the fundamental mechanisms implied in flapping based propulsion systems. We use a simplified model, which consists of a flapping foil, placed in a hydrodynamic tunnel. This set up allows us to establish a framework for the analyse of wakes produced. Particularly, we are interested with the influence of the foil flexibility on these wakes. We define a 2D phase space (frequency and amplitude of the flapping), in which we identify three main flow regimes, associated with three vortices wake type. The PIV technique allows us to precisely analyse and quantify the physical and geometrical parameters of the observed wakes. The mean force is estimated for each regime, using a standard momentum balance. We localise then the drag-propulsion transition in our phase space. We show that the propulsive performance of flexible foils is superior to that of the rigid foil, and we suggest some explanations to explain this result.
Olivier Doaré (Examinateur) ENSTA, Palaiseau
Marie Farge (Examinatrice) ENS, Paris
Stéphane Popinet (Rapporteur) NIWA, New Zealand
Lionel Schouveiler (Rapporteur) IRPHE, Marseille
José Eduardo Wesfreid (Directeur de thèse) PMMH, Paris
Ramiro Godoy-Diana (Co-Directeur de thèse) PMMH, Paris