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”
Simple phalanx pattern leads to energy saving in cohesive fish schooling
I. Ashraf, H. Bradshaw, T. T. Ha, J. Halloy, R. Godoy-Diana, B. Thiria
PNAS 114 (36) 9599-9604 (2017)
Synchronisation and collective swimming patterns in Hemigrammus bleheri
I. Ashraf, R. Godoy-Diana, J. Halloy, B. Collignon, B. Thiria
Journal of the Royal Society Interface 13 20160734 (2016)
The question of how individuals in a population organize when living in groups arises for systems as different as a swarm of microorganisms or a flock of seagulls. The different patterns for moving collectively involve a wide spectrum of reasons, such as evading predators or optimizing food prospection. Also, the schooling pattern has often been associated with an advantage in terms of energy consumption. We use a popular aquarium fish, the red nose tetra fish, Hemigrammus bleheri, which is known to swim in highly cohesive groups, to ana- lyze the schooling dynamics. In our experiments, fish swim in a shallow-water tunnel with controlled velocity, Continue reading “Synchronisation and pattern formation in fish swimming”
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”
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”
Topology-induced effect in biomimetic propulsive wakes
V. Raspa; R. Godoy-Diana & B. Thiria.
Journal of Fluid Mechanics, 729: 377-387 (2013).
Abstract: It is known that the wake pattern observed in a cross-section behind swimming or flying animals is typically characterized by the presence of periodical vortex shedding. However, depending on species, propulsive wakes can differ according to the spatial ordering of the main vortex structures. We conducted a very precise experiment to analyse the role of the topology of the wake in the generation of propulsion by comparing two prototypical cases in a quasi-two-dimensional view. Continue reading “Topology-induced effect in biomimetic propulsive wakes”
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”