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 study. The model array is first characterised by evaluating the role played by various parameters (configuration, flexibility, wave frequency) on the energy distribution in our system. Following these first observations, an interference model is then developed in order to describe the observed global effects of the array on both the wave field and the blade dynamics, based on known local parameters of a unit item of the array. This model then serves as a tool for exploring many possible array configurations, in order to determine the optimal choice regarding both the attenuation and the absorption of the imposed waves. A final experimental study is presented, in which the key results from the interference model are evaluated and the underlying principles of array optimisation are identified.
Médéric Argentina (Institut de Physique de Nice) Rapporteur
Olivier Doaré (ENSTA ParisTech) Rapporteur
Aurélien Babarit (École Centrale de Nantes) Examinateur
Delphine Doppler (Université Claude Bernard Lyon 1) Examinatrice
Sandra Lerouge (Université Paris Diderot) Examinatrice
William Megill (Hochschule Rhein-Waal) Examinateur
Gaële Perret (Université du Havre) Examinatrice
Ramiro Godoy-Diana (ESPCI Paris) Directeur de thèse
Benjamin Thiria (ESPCI Paris) Directeur de thèse
Surface wave energy absorption by a partially submerged bio-inspired canopy
C. Nové-Josserand, F. Castro Hebrero, L.-M. Petit, W. Megill, R. Godoy-Diana & B. Thiria
Bioinspiration & Biomimetics 13 036006 (2018)
Aquatic plants are known to protect coastlines and riverbeds from erosion by damping waves and fluid flow. These flexible structures absorb the fluid-borne energy of an incoming fluid by deforming mechanically. In this paper we focus on the mechanisms involved in these fluid-elasticity interactions, as an efficient energy harvesting system, using an experimental canopy model in a wave tank.We study an array of partially-submerged flexible structures that are subjected to the action of a surface wave field, investigating in particular the role of spacing between the elements of the array on the ability of our system to absorb energy from the flow. The energy absorption potential of the canopy model is examined using global wave height measurements for the wave field and local measurements of the elastic energy based on the kinematics of each element of the canopy. We study different canopy arrays and show in particular that flexibility improves wave damping by around 40%, for which half is potentially harvestable.
On the diverse roles of fluid dynamic drag in animal swimming and flying
R. Godoy-Diana & B. Thiria
Journal of the Royal Society Interface 15 20170715 (2018)
Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. Continue reading “Fluid dynamic drag in animal swimming and flying”
Modelling of an actuated elastic swimmer
M. Piñeirua, B. Thiria & R. Godoy-Diana
Journal of Fluid Mechanics 829 731-750 (2017)
We studied the force production dynamics of undulating elastic plates as a model for fish-like inertial swimmers. Using a beam model coupled with Lighthill’s large-amplitude elongated-body theory, we explore different localised actuations at one extremity of the plate (heaving, pitching and a combination of both) in order to quantify the reactive and resistive contributions to the thrust. The latter has the Continue reading “Flapping elastic plates as a model of fish-like swimmers”
Resistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers
M. Piñeirua, R. Godoy-Diana & B. Thiria
Physical Review E 92 021001(R) (2015).
We address here a crucial point regarding the description of moderate to high Reynolds numbers aquatic swimmers. For decades, swimming animals have been classified in two different families of propulsive mechanisms based on the Reynolds number: the resistive swimmers, using local friction to produce the necessary thrust force for locomotion at low Reynolds number, and the reactive swimmers, lying in the high Reynolds range, and using added mass acceleration (described by perfect fluid theory). Continue reading “Resistive thrust production can be as crucial as added mass mechanisms for inertial undulatory swimmers”
Four-winged flapping flyer in forward flight
R. Godoy-Diana, P. Jain, M. Centeno, A. Weinreb & B. Thiria
In Klapp et al. (eds.), Selected Topics of Computational and Experimental Fluid Mechanics, Environmental Science and Engineering, pp. 147-158. Springer (2015).
We study experimentally a four-winged flapping flyer with chord-wise flexible wings in a self-propelled setup. For a given physical configuration of the flyer (i.e. fixed distance between the forewing and hindwing pairs and fixed wing flexibility), we explore the kinematic parameter space constituted by the flapping frequency and the forewing-hindwing phase lag. Continue reading “Four-winged flapping flyer in forward flight”
Large-amplitude undulatory swimming near a wall
R. Fernández-Prast, V. Raspa, B. Thiria, F. Huera-Huarte & R. Godoy-Diana. Bioinspiration and Biomimetics 10 016003 (2015).
We study experimentally the propulsive dynamics of flexible undulating foils in a self-propelled swimming configuration near a wall. Measurements of swimming speed and propulsive force are performed, together with full recordings of the elastic wave kinematics and particle image velocimetry. Continue reading “Undulatory swimming near a wall”
Bio-inspired swimming and flying – Vortex dynamics and fluid/structure interaction
Habilitation à diriger des recherches, Université Pierre et Marie Curie, 2014.
PDF file here (19.4 MB)
The present document, prepared in view of obtaining the Habilitation à diriger des recherches, reviews my main research subject at PMMH since 2006, which concerns the study of swimming and flying inspired by nature. Canonical examples of flapping flight and undulatory swimming are explored using simplified experimental models as a starting point. This allows for the discussion of some fundamental questions related to the physics of bio-inspired locomotion at “intermediate” Reynolds numbers. In particular, we address the strong fluid-structure interactions that arise in these problems, where we have focused on: simplified models of flapping foils in hydrodynamic tunnel experiments, especially in the dynamics of vorticity in the wake of an oscillating foil ; mechanical models of flapping flyers with flexible wings in a self-propelled configuration (in the spirit of the pioneer experiments of Etienne-Jules Marey), as well as novel experimental models of undulatory swimming.
Continue reading “Habilitation à diriger des recherches (HDR)”
Elastic swimmer on a free surface
S. Ramananarivo, B. Thiria & R. Godoy-Diana.
Physics of Fluids, 26: 091112 (2014)
*31st Annual Gallery of Fluid Motion (Pittsburgh, Pennsylvania, USA, 2013)
Vortex-induced drag and the role of aspect ratio in undulatory swimmers
V. Raspa, S. Ramananarivo, B. Thiria & R. Godoy-Diana. Physics of Fluids, 26 : 041701 (2014).
During cruising, the thrust produced by a self-propelled swimmer is balanced by a global drag force. For a given object shape, this drag can involve skin friction or form drag, both being well-documented mechanisms. However, for swimmers whose shape is changing in time, the question of drag is not yet clearly established. Continue reading “Drag in undulatory swimmers”
Propagating waves in bounded elastic media: an application to the efficiency of bio-inspired swimmers
S. Ramananarivo, R. Godoy-Diana & B. Thiria.
EPL, 105 : 54003 (2014).
Confined geometries usually involve reflected waves interacting together to form a spatially stationary pattern. Our recent study on the locomotion of a self-propelled elastic swimmer on a free surface [Ramananarivo et al. 2013], however, has shown that propagating wave kinematics can naturally emerge in a forced elastic rod, even with boundary conditions involving significant reflections. This particular behavior is observed only in the presence of strong damping. Continue reading “Propagating waves in bounded elastic media”
Passive elastic mechanism to mimic fish-muscles action in anguilliform swimming
S. Ramananarivo; R. Godoy-Diana & B. Thiria.
Journal of the Royal Society Interface 10 : 20130667 (2013).
Abstract: Swimmers in nature use body undulations to generate propulsive and maneuvering forces. The an- guilliform kinematics is driven by muscular actions all along the body, involving a complex temporal and spatial coordination of all the local actuations. Such swimming kinematics can be reproduced artificially, in a simpler way, by using passively the elasticity of the body. Here we present experiments on self-propelled elastic swimmers at a free surface in the inertial regime. Continue reading “Passive elastic mechanism to mimic fish-muscles action in anguilliform swimming”
Stabilizing effect of flexibility in the wake of a flapping foil
C. Marais; B Thiria; Wesfreid, J. E. & R. Godoy-Diana.
Journal of Fluid Mechanics, 710 : 659-669 (2012).
Abstract: The wake of a flexible foil undergoing pitching oscillations in a low-speed hydrodynamic tunnel is used to examine the effect of chordwise foil flexibility in the dynamical features of flapping-based propulsion. Continue reading “Stabilizing effect of flexibility in the wake of a flapping foil”
Rather than resonance, flapping wing flyers may play on aerodynamics to improve performance
S. Ramananarivo; R. Godoy-Diana & B. Thiria.
Proceedings of the National Academy of Sciences (USA), 108 (15): 5964-5969 (2011).
Abstract: Saving energy and enhancing performance are secular preoccupations shared by both nature and human beings. In animal locomotion, flapping flyers or swimmers rely on the flexibility of their wings or body to passively increase their efficiency using an appropriate cycle of storing and releasing elastic energy. Despite the convergence of many observations pointing out this feature, the underlying mechanisms explaining how the elastic nature of the wings is related to propulsive efficiency remain unclear. Here we use an experiment with a self-propelled simplified insect model allowing to show how wing compliance governs the performance of flapping flyers. Continue reading “Behind the performance of flapping wing flyers”
How wing compliance drives the efficiency of self-propelled flapping flyers
B. Thiria & R. Godoy-Diana.
Physical Review E, 82 : 015303(R) (2010).
*arXiv preprint blogged in MIT Technology Review (March 2, 2010)
*Also referenced in Vir. J. Bio. Phys. Res. / Volume 20 / Issue 3 / (August 1, 2010)
Abstract: Wing flexibility governs the flying performance of flapping-wing flyers. Here, we use a self-propelled flapping-wing model mounted on a ”merry go roun” to investigate the effect of wing compliance on the propulsive efficiency of the system. Continue reading “Bending to fly”