Sophie Ramananarivo’s PhD: Propulsion biomimétique de structures élastiques

PhD defense on January 10, 2014 at ESPCI

Propulsion biomimétique de structures élastiques

Sophie Ramananarivo


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)