Membre de l’équipe Matière Molle & Biophysique, thématique Instabilités et Turbulence.

 

Overview
My favorite activities concern mechanics and/or fluids problems for which there is a promising perspective for the experimental approach. Such problems are easily found in nonlinear and out-of-equilibrium systems.

keywords : instability, interacting particles, turbulence, slender structure

Research activities

Sedimentation of spherical particles falling non vertically

If a spherical heavy particle is released in a fluid at rest, a variety of non-trivial trajectories may be observed (oblique, oscillating or chaotic motions). These non-vertical paths are related to the interplay between the particle motion and the wake structure that depends, among other parameters, of the viscosity of the fluid.

Transition paths of individual particles falling in viscosity-stratified fluid

A water mixture is prepared in a columnar tank so that the viscosity is continuously varied from a high a value at the free surface to a low value at the bottom of the tank. An individual particle falling in the stratified fluid overgoes a path transition from a vertical falling regime to a oblique settling regime in the lowest part of the tank. The consequences of fluid entrainment is discussed as the origin of a delay for the establishment of the oblique regime.

Trajectories of individual spheres released in a viscosity-stratified fluid.

Columnar structures for dilute suspensions of particle falling in the oblique regime

A set of particles is released (glass beads, 2 mm) in a fluid at rest with a viscosity such a single particle would fall in the oblique regime. For a relativelly low particle concentration (volumic fraction 10-3 to 10-4), the particles organize in columnar structures. The origin of this collective behaviour is attributed to the particle-particle wake interactions whose statistical occurence is enhanced because of the non vertical exploration of the particles in the non-vertical regime.

Trajectories in sedimenting suspension (top view, scale bar 2 cm).

Reconfiguration

Reconfiguration refers to the behaviour of deformable structures in high-velocity fluid flows. The main field of interest is botany as reconfiguration can be presented as a survival strategy adopted by plants not to be damaged in high winds (Lafontaine’s Le chêne et le roseau happens to be, beyond poetry, a very good introduction to the concept of reconfiguration).

 

An effective reconfiguration experiment with a rigid sphere trapped in a jet

If someone wants to let think that science is somehow magic, levitation is a good option. One can use for instance the turbulent jet of a hair dryer oriented upward to capture and manipulate a ping-pong ball. The fluid forces in  a turbulent jet has some remarkable properties which makes that moving a sphere on the jet axis is somehow equivalent to change its size without moving it. This principle is used to build an analogy between the problem of a rigid sphere free to find an equilibrium position in a turbulent jet and the problem of an effective deformable sphere free to find its shape in a stationnary flow.

 

3 spheres that would experience the same fluid forces in the jet

 

Reconfiguration in the constant drag regime

For a plant in the wind, the deformability makes that the relation between drag force F and velocity v is not the usual FR ~ v2 that would be measured for a rigid body (R). Actually, forces for soft objets (S) are found to obey a similar scaling relation where FS ~ v2-E where the exponant 2 is a reduced by a so called Vogel exponent E, that is typically of order 1 for soft elastic structure (plates, rod, leaves, branches, …). The outreach of this work was to show that it is possible to design a deformable structure for which the Vogel exponent equals 2 which means that the drag on the structure is independent of the flow velocity.

 

Drag force for a flexible weighted ribbon towed at constant velocity.

Elasticity of thin plates: curvature-induced rigidity

A thin elastic plate like a sheet of paper can be easily bent by its own weight. To avoid this situation, newspaper readers have developped a well-known trick (figure, imaget 1) that is to impose a transverse curvature to the newspaper sheet they are reading. The same trick is also observed in plants (figure, imaget 1) with leaves shaped as long strips (yucca, maize, …).  In this work, a thin elastic strip has been pressed onto a curved frame. The curvature imposed by the clamping is smoothly decreasing and after a given distance, the ribbon is flat. In terms of mechanical properties, it means that the sheet is rigid with respect to bending in the curved region and soft and easily bent by gravity in the flat terminal portion.

1) Studio actor performing the newspaper trick. 2) Yucca plant. Bottom image: snapshot of an artificial leaf made of a strip transversly curved (those might be used in fake plastic trees for which, apparently, gravity allways wins).

Nanomechanics

Frequency-driving of mechanical resonators

Silicon carbide nanowires are used as mechanical resonators. The vibration modes are observed by the harmonic forcing for some specific frequencies. The forcing is coming from an oscillating electric field applied between the nanowire and a counter-electrode next to it. The mechanical damping has been specifically investigated and it was shown that the electric forcing scheme may introduce additionnal mechanical damping.

Mechanical resonances of a silicon carbide nanowire (driving frequencies: 7.2 kHz, 39.5 kHz and 107.6 kHz). Scale bar 50 µm.

 

Self-oscillation

A self-oscillator may be presented as a device that generates an oscillating output from a continuous driving. If a strong electric field is applied to a silicon carbide nanowire, a significant DC current is estalished that may eventually lead to self-oscillation. This spontaneous oscillation is characterized by a mechanical oscillation and an oscillating AC component in the current at the same frequency selected by the electromechanical system.

 

 

Self-oscillation observed in the « musketeer » geometry under a DC bias of 15 Volts. Scale bar 50 µm.

External synchronization

A self-oscillator is a nonlinear system by principle since a nonzero-frequency emerges from a zero-frequency driving. If an additional external frequency forcing fe is imposed to a self-oscillator with frequency fo two situations are possible: either fe is too far from fo and the self-oscillator keeps its frequency fo, either fe is close enough and a synchronized state emerges where the self-oscillator adopts the frequency of the external driving fe.

Response to phase shift

Phase-time diagram of a synchronized nanowire. A discontinuity is introduced in the external forcing signal to observe the dynamics of the synchronized phase.

Noise-induced phase jumps

Phase shift (in cycles) between the self-oscillator and the external driving over time. Phase synchronization corresponds to the horizontal steps. Self-oscillation period ~ 30 µs.

 

 

 

Publications

Published articles

List of my publications on Hal Archiv

2017

Equilibrium position of a rigid sphere in a turbulent jet: A problem of elastic reconfiguration
Thomas Barois, Peter D. Huck, Mickaël Bourgoin, Romain Volk
Physical Review E PDF

Investigation of the small-scale statistics of turbulence in the Modane S1MA wind tunnel
M Bourgoin, C Baudet, S Kharche, N Mordant, T Vandenberghe, S Sumbekova, N Stelzenmuller, A Aliseda, M Gibert, P-E Roche, R Volk, T Barois, M Lopez Caballero, L Chevillard, J-F Pinton, L Fiabane, J Delville, C Fourment, A Bouha, L Danaila, E Bodenschatz, G Bewley, M Sinhuber, A Segalini, R Örlü, I Torrano, J Mantik, D Guariglia, V Uruba, V Skala, J Puczylowski, J Peinke
CEAS Aeronautical Journal PDF

2016

Columnar structure formation of a dilute suspension of settling spherical particles in a quiescent fluid
Sander Huisman, Thomas Barois, Mickaël Bourgoin, Agathe Chouippe, Todor Doychev, Peter Huck, Carla Bello Morales, Markus Uhlmann, and Romain Volk
Physical Review Fluids PDF

Quality-Factor Enhancement of Nanoelectromechanical Systems by Capacitive Driving Beyond Resonance
Thomas Barois, Sorin Perisanu, Philippe Poncharal, Philippe Vincent, Stephen Purcell, and Anthony Ayari
Physical Review Applied PDF

2014

How a Curved Elastic Strip Opens
Thomas Barois, Loïc Tadrist, Catherine Quilliet, and Yoël Forterre
Physical Review Letters PDF

Frequency modulated self-oscillation and phase inertia in a synchronized nanowire mechanical resonator
Thomas Barois, Sorin Perisanu, Philippe Vincent, Stephen Purcell, and Anthony Ayari
New Journal of Physics PDF

2013

Role of fluctuations and nonlinearities on field emission nanomechanical self-oscillators
Thomas Barois, Sorin Perisanu, Philippe Vincent, Stephen Purcell, and Anthony Ayari
Physical Review B PDF

Flexible body with drag independent of the flow velocity
Thomas Barois and Emmanuel de Langre
Journal of Fluid Mechanics PDF

Ultra Low Power Consumption for Self-Oscillating Nanoelectromechanical Systems Constructed by Contacting Two Nanowires
Thomas Barois, Anthony Ayari, Pascal Vincent, Sorin Perisanu, Philippe Poncharal, and Stephen Purcell
Nanoletters PDF

2012

Carbon nanotube nanoradios: The field emission and transistor configurations
Pascal Vincent, Anthony Ayari, Philippe Poncharal, Thomas Barois, Sorin Perisanu, Vincent Gouttenoire, and Stephen Purcell
Comptes Rendus Physique PDF

Electron Fluctuation Induced Resonance Broadening in Nano Electromechanical Systems: The Origin of Shear Force in Vacuum
Alessandro Siria, Thomas Barois, Kenny Vilella, Sorin Perisanu, Anthony Ayari, Dominique Guillot, Stephen Purcell, and Philippe Poncharal
Nanoletters PDF

Ohmic electromechanical dissipation in nanomechanical cantilevers
Thomas Barois, Anthony Ayari, Alessandro Siria, Sorin Perisanu, Pascal Vincent, Philippe Poncharal, and Stephen Purcell
Physical Review B PDF

2011

Performance of field-emitting resonating carbon nanotubes as radio-frequency demodulators
Pascal Vincent, Philippe Poncharal, Thomas Barois, Sorin Perisanu, Vincent Gouttenoire, Henri Frachon, Anthony Lazarus, Emmanuel de Langre, Eric Minoux, Mickaël Charles, Afshin Ziaei, Dominique Guillot, May Choueib, Anthony Ayari, and Stephen Purcell
Physical Review B PDF

The mechanical resonances of electrostatically coupled nanocantilevers
Sorin Perisanu, Thomas Barois, Philippe Poncharal, Thibaut Gaillard, Anthony Ayari, Stephen Purcell, and Pascal Vincent
Applied Physics Letters PDF

2010

Simple modeling of self-oscillations in nanoelectromechanical systems
Arnaud Lazarus, Thomas Barois, Sorin Perisanu, Philippe Poncharal, Paul Manneville, Emmanuel de Langre, Stephen Purcell, Pascal Vincent, and Anthony Ayari
Applied Physics Letters PDF

Digital and FM Demodulation of a Doubly Clamped Single‐Walled Carbon‐Nanotube Oscillator: Towards a Nanotube Cell Phone
Vincent Gouttenoire, Thomas Barois, Sorin Perisanu, Jean‐Louis Leclercq, Stephen T Purcell, Pascal Vincent, and Anthony Ayari
Small PDF

Beyond the linear and Duffing regimes in nanomechanics: Circularly polarized mechanical resonances of nanocantilevers
Sorin Perisanu, Thomas Barois, Anthony Ayari, Philippe Poncharal, May Choueib, Stephen Purcell, and Pascal Vincent
Physical Review B PDF

Conference proceedings

2015

Field emission as a tool for exploring new phenemena in nanomechanics
Pascal Vincent, Anthony Ayari, Sorin Perisanu, Philippe Poncharal, Thomas Barois, Arnaud Derouet, May Choueib, Stephen Purcell
Vacuum Nanoelectronics Conference (IVNC), 2015 28th International

2014

Synchronization of nanowire self-oscillators
Anthony Ayari, Thomas Barois, Sorin Perisanu, Pascal Vincent, and Stephen Purcell
General Assembly and Scientific Symposium (URSI GASS), 2014 XXXIth URSI

2012

Signal amplification in a synchronized field emission NEMS
Thomas Barois, Sorin Perisanu, Philippe Poncharal, Pascal Vincent, Stephen Purcell, Anthony Ayari
2012 International Conference on Electromagnetics in Advanced Applications

Talks

Conferences & Seminars
– Consonance, dissonance et distances (main speaker: Nicolas Trottignon), Séminaire détente mathématique – Maison de l’Informatique et des Mathématiques, Fev. 2016, Lyon.
– The mechanics of plants: what we can learn from thin elastic strips (MSC Paris Diderot, Mar. 2015 – IPR Rennes, April 2015- IMFT Toulouse, April 2015 – LOMA, May 2015 – ILM Lyon, Dec. 2015 – Univ. Liège, Apr. 2016).
– Experimental Investigation of Small-Scale Homogeneous Isotropic Turbulence in S1MA wind tunnel – CEAS 2015, Delft TU.
– Flexible body with drag independent of the flow velocity – APS-DFD Meeting Pittsburgh, Nov. 2013.
– Nanomechanics of carbon nanotubes: an excitation technique based on telecommunication signals – Trans’Alp nano, Como, Italy, May 2010.
– Detection of mechanical resonances of doubly-clamped carbon nanotubes by FM techniques (poster) – GDR Nanotubes & Graphene – Coma ruga, Spain, Sept. 2009.

Internal seminars
– Investigation of small scale turbulence in equipments designed for aircrafts testing – ENS Lyon Sept 2015.
– The shape of thin things: experiments with elastic, plastic, and viscous systems – Laboratoire Écoulement Géophysiques et Industriels, Grenoble, Apr. 2014.
– Drag reduction: a flexible body with drag independent of the flow velocity – Laboratoire Écoulement Géophysiques et Industriels, Grenoble, Oct. 2013.

Peoplaborators

Local:
Hamid Kellay
Juho Lintuvuori
Jean-François Boudet

Elsewhere:
Anthony Ayari, Pascal Vincent, Sorin Perisanu, Philippe Poncharal, Stephen Purcell (ILM, Lyon)
Emmanuel de Langre (LadHyX, Palaiseau)
Loïc Tadrist (Microfluidics Lab, Univ. Liège)
Catherine Quilliet (Liphy, Grenoble)
Yoël Forterre (IUSTI, Marseille)
Nicolas Mordant (LEGI, Univ. Grenoble)
Mathieu Gibert (Institut Néel, Grenoble)
Mickaël Bourgoin, Romain Volk, Peter Huck, Sander Huisman (Lab. physique, ENS Lyon)
Markus Uhlmann, Agathe Chouippe (KIT, Karlsruhe)
Yvan Dossmann (LEMTA, Univ. Nancy)

 

CV

Faculty positions

since 2016: Permanent researcher at LOMA (CR2/CNRS)
2014 – 2016 : Postdoc Laboratoire de Physique (ENS Lyon)
2013 – 2014 : Postdoc LEGI (Grenoble)
2012 – 2013 : Postdoc LadHyX (Palaiseau)
2009 – 2012 : PhD student LPMCN (now ILM) (Univ. Lyon 1)

Education & Internships

2008 : Agrégation de Physique
2007 : Internship, Univ. de Chile, Santiago de Chile
2006 : Internship, Lab. Of the Future (Pessac)
2005 – 2008 : Studentship at École Normale Supérieure (Lyon)

Thesis here

 

barois-thomas

Thomas BAROIS

Laboratoire Ondes et Matière d’Aquitaine (LOMA)
351 cours de la libération
33405 Talence Cedex

Phone : + 33 (0)5 40 00 6508
E-mail: thomas.barois@u-bordeaux.fr