Sophie Ramananarivo

École Polytechnique · Département de Mécanique

We designed and built a reduced-scale model experiment to study the paragliding inflation and launching phase at given traction force. We show that the launch trajectory of a single skin glider is universal, that is, independent of the exerted force. As a consequence, the length of the take-off run required for the glider to reach its “ready to lau...

We investigate the three-dimensional flow around and through a porous screen for various porosities at high Reynolds number Re = O(10000). Historically, the study of this problem was focused on two-dimensional cases and for a screen spanning completely or partially a channel. Since many recent problems have involved a porous object in a three-dimen...

Mechanisms of drag reduction through shape reconfiguration have been extensively studied on model geometries of plates and beams that deform primarily in bending. Adding an origami crease pattern to such plates produces a distinct class of deformation modes, with large shape changes along selected degrees of freedom. Here, we investigate the impact...

Fog harvesting is an application of aerosol filtration to capture water droplets from fog by using nets, called fog collectors. It is a promising technique for freshwater supply in arid and semi-arid regions. In this study, we investigate the collection efficiency of harp-like fog collectors consisting of vertical fibres. We conduct well-controlled...

We design, build and run a reduced-scale model experiment to study the paragliding inflation and launching phase at given traction force. We show that the launch trajectory of the glider is universal, that is, independent of the strength of the exerted force. As a consequence, the length of the take-off run required for the glider to reach its "rea...

We investigate the deformation in a uniform water flow of thin sheets perforated with parallel cuts. Through combined experiments and theory, we show that deployment is governed by the competition between fluid forces and sheet stretchability, which is prescribed by the cut pattern. Importantly, fluid loading is modulated by the local three-dimensi...

For a couple of decades, passive fog collectors (generally a fibrous mesh placed in the path of the fog) have been used to obtain data from fog or to harvest fresh water, for domestic use of for agriculture. Here, we present in situ force measurements on a model fog collector, composed of vertical fibers with a 40% solidity. We compare in situ wind...

The flagella of microorganisms have provided inspiration for many synthetic devices, but they’re typically not easy to produce. A new class of swimmer makes it look simple by spontaneously growing a tail that it can whip to self-propel.

Active navigation relies on effectively extracting information from the surrounding environment, and often features the tracking of gradients of a relevant signal-such as the concentration of molecules. Microfluidic networks of closed pathways pose the challenge of determining the shortest exit pathway, which involves the proper local decision-maki...

Molecular motors are essential to the living, they generate additional fluctuations that boost transport and assist assembly. Self-propelled colloids, that consume energy to move, hold similar potential for the man-made assembly of microparticles. Yet, experiments showing their use as a powerhouse in materials science lack. Our work explores the de...

Molecular motors are essential to the living, generating fluctuations that boost transport and assist assembly. Active colloids, that consume energy to move, hold similar potential for man-made materials controlled by forces generated from within. Yet, their use as a powerhouse in materials science lacks. Here we show a massive acceleration of the...

Aeronautical studies have shown that subtle changes in aerofoil shape substantially alter aerodynamic forces during fixed-wing flight. The link between shape and performance for flapping locomotion involves distinct mechanisms associated with the complex flows and unsteady motions of an air- or hydro-foil. Here, we use an evolutionary scheme to mod...

Advances in colloidal synthesis allow for the design of particles with controlled patches. This article reviews routes towards colloidal locomotion, where energy is consumed and converted into motion, and its implementation with active patchy particles. A special emphasis is given to phoretic swimmers, where the self-propulsion originates from an i...

Classic models of fish schools and flying formations of birds are built on the hypothesis that the preferred locations of an individual are determined by the flow left by its upstream neighbor. Lighthill posited that arrangements may in fact emerge passively from hydro- or aerodynamic interactions, drawing an analogy to the formation of crystals by...

• Roots play an important role in strengthening and stabilizing soils. Existing models predict that tensile strength and root abundance are primary factors that strengthen soil. This study quantified how both factors are affected by root developmental stage.• Focusing on early development of Avena fatua, a common grassland species with a fibrous ro...

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. We address this problem by...

Confined geometries usually involve reflected waves interacting together to form a spatially stationary pattern. A recent study on bio-locomotion, however, has reported that propagating wave kinematics can naturally emerge in a forced elastic rod, even with boundary conditions involving significant reflections. It has been shown that this particula...

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...

Swimmers in nature use body undulations to generate propulsive and manoeuvring forces. The anguilliform 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 the elasticity of...

This project was conducted to increase understanding of the effect of root development on soil stability. Root development and relevant morphological and mechanical plant attributes were monitored in conjunction with the evolution of soil shear resistance. Avena fatua (wild oats) were grown in pots for one, three, and seven weeks, after which soil...

We present in this fluid dynamics video a novel experimental setup with self-propelled swimmers on a free surface. The swimmers, modeled as flexible thin filaments, are subjected to external electromagnetic forcing driving a propagating elastic wave that gives rise to self- propulsion. The fluid-structure interaction problem of these passive anguil...

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 observa...