Levan Jibuti - Academia.edu (original) (raw)
Papers by Levan Jibuti
et codirigée par Salima Rafaï préparée au sein du Laboratoire interdisciplinaire de Physique dans... more et codirigée par Salima Rafaï préparée au sein du Laboratoire interdisciplinaire de Physique dans Ecole Doctorale de Physique Locomotion et écoulements dans les fluides complexes confinés Thèse soutenue publiquement le 21 Octobre 2011, devant le jury composé de:
Cette these est consacree a l'etude de la dynamique et de la rheologie des fluides complexes.... more Cette these est consacree a l'etude de la dynamique et de la rheologie des fluides complexes. Nous utilisons une methode de simulation numerique a trois dimensions. Les systemes que nous etudions ici sont des suspensions de micro-nageurs actifs, des suspensions de particules spheriques rigides en presence d'un champ externe auquel elles sont sensibles et de la dynamique de suspensions de particules spheriques et confinees en cisaillement. Les Micro-nageurs sont les objets microscopiques qui se propulsent dans un fluide et ils sont omnipresents dans la nature. Un exemple commun de micro-nageurs est la micro-algue textit{Chlamydomonas} . Un des buts principaux de cette these est de comprendre l'effet de la motilite de ces micro-organismes sur les proprietes macroscopiques globales de la suspension, telles que la viscosite effective pour expliquer les observations experimentales. Nous avons elabore differents modeles de suspensions de textit{Chlamydomonas} et effectue des s...
Measuring quantitative and macroscopic parameters to estimate the global motility of a large popu... more Measuring quantitative and macroscopic parameters to estimate the global motility of a large population of swimming cells is a challenge. The rheology of suspensions containing such cells is a good solution to achieve such measurements. As a matter of fact, recent rheological measurements on suspensions of bacteria [1] or algae [2] have been performed very recently. These experiments showed the
Physical review. E, 2017
Micro-organisms usually can swim in their liquid environment by flagellar or ciliary beating. In ... more Micro-organisms usually can swim in their liquid environment by flagellar or ciliary beating. In this numerical work, we analyze the influence of flagellar beating on the orbits of a swimming cell in a shear flow. We also calculate the effect of the flagellar beating on the rheology of a dilute suspension of microswimmers. A three-dimensional model is proposed for Chlamydomonas Reinhardtii swimming with a breaststroke-like beating of two anterior flagella modeled by two counter-rotating fore beads. The active swimmer model reveals unusual angular orbits in a linear shear flow. Namely, the swimmer sustains orientations transiently across the flow. Such behavior is a result of the interplay between shear flow and the swimmer's periodic beating motion of flagella, which exert internal torques on the cell body. This peculiar behavior has some significant consequences on the rheological properties of the suspension. We calculate Einstein's viscosity of the suspension composed of ...
Physical Review Fluids, 2016
sphériques en présence d'un couple externe. Nous avons montré que le changement de vitesse angula... more sphériques en présence d'un couple externe. Nous avons montré que le changement de vitesse angulaire des particules due à l'application d'un couple externe est suisante pour modier fortement la viscosité de la suspension. Basée sur des simulations numériques, une formule semi-empirique a été proposée pour la viscosité des suspensions de particules sphériques valables jusqu'à 40% de concentration. Nous avons également montré que la 2ème loi de Faxén peut être étendue par une expression empirique pour de grandes concentrations.
Measuring quantitative and macroscopic parameters to estimate the global motility of a large popu... more Measuring quantitative and macroscopic parameters to estimate the global motility of a large population of swimming cells is a challenge. The rheology of suspensions containing such cells is a good solution to achieve such measurements. As a matter of fact, recent rheological measurements on suspensions of bacteria [1] or algae [2] have been performed very recently. These experiments showed the
Physical Review E, 2014
Three-dimensional (3D) numerical simulations are performed on suspensions composed of puller-like... more Three-dimensional (3D) numerical simulations are performed on suspensions composed of puller-like microswimmers that are sensitive to light (phototaxis) mimicking microalgae in a Poiseuille flow. Simulations are based on the numerical resolution of the flow equations at low Reynolds numbers discretized on a 3D grid (finite differences). The model reproduces the formation of a central jet of swimmers by self-focusing [Phys. Rev. Lett. 110, 138106 (2013)] but also predicts an instability of the jet, which leads to its fractionation in clusters. We show that this instability is due to hydrodynamic interactions between microswimmers, which attract each other along the flow direction. This effect was not observed in the experiments conducted on dilute suspensions (i.e., where hydrodynamic interactions are weak). This phenomenon is peculiar for pullers for which collective motions are usually not observed on such a time scale. With this modeling, we hope to pave the way toward a better understanding of concentration techniques of algae (a bottleneck challenge in industrial applications).
A three-dimensional model is proposed for Chlamydomonas Reinhardtii swimming with a breaststroke-... more A three-dimensional model is proposed for Chlamydomonas Reinhardtii swimming with a breaststroke-like beating of its two flagella. The model reveals unusual angular orbits of the active swimmer under a linear shear flow. Namely, the swimmer sustains orientation transiently across the flow when flagella plane is perpendicular to the shear plane, and amplify the shear-induced rotation along the flow. Such behavior is a result of the interplay between shear-induced deformation and swimmer's periodic beating motion that exerts internal torques on the torque-free swimmer. This particular behavior has some significant consequences on the rheological properties of the suspension that tends to confirm previous experimental results [Phys. Rev. Lett. 104, 098102 (2010)]. We calculated the intrinsic viscosity of the suspension with such isolated modeled microswimmers (dilute case) in shear flow using numerical simulations based on Rotne-Prager approximation. The results show an increased intrinsic viscosity for active swimmer suspensions in comparison to non-active ones in accordance with previous experimental measurements. A major enhancement of the active swimmer viscosity occurs due to the effectively extended shape of the deformable swimming cells. We also recover the experimentally observed shear thinning behavior.
Measuring quantitative and macroscopic parameters to estimate the global motility of a large popu... more Measuring quantitative and macroscopic parameters to estimate the global motility of a large population of swimming cells is a challenge. The rheology of suspensions containing such cells is a good solution to achieve such measurements. As a matter of fact, recent rheological measurements on suspensions of bacteria [1] or algae [2] have been performed very recently. These experiments showed the
Physical Review Letters, 2010
The measurement of a quantitative and macroscopic parameter to estimate the global motility of a ... more The measurement of a quantitative and macroscopic parameter to estimate the global motility of a large population of swimming biological cells is a challenge Experiments on the rheology of active suspensions have been performed. Effective viscosity of sheared suspensions of live unicellular motile micro-algae (Chlamydomonas Reinhardtii) is far greater than for suspensions containing the same volume fraction of dead cells and suspensions show shear thinning behaviour. We relate these macroscopic measurements to the orientation of individual swimming cells under flow and discuss our results in the light of several existing models.
Physical Review Letters, 2013
We study the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids i... more We study the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids in a dynamic magnetic field. The sedimented ribbon assembles due to time averaged dipolar interactions between the beads. The time dependence of the dipolar interactions together with hydrodynamic interactions cause a twisted ribbon conformation. Domain walls of high twist connect domains of nearly constant orientation and negligible twist and travel through the ribbon. The particular form of the domain walls can be controlled via the frequency and the eccentricity of the modulation. The flux of twist wallsa true ribbon property absent in slender bodies-provides the thrust onto the surrounding liquid that propels this biomimetic flagellum into the opposite direction. The propulsion efficiency increases with frequency and ceases abruptly at a critical frequency where the conformation changes discontinuously to a flat standing ribbon conformation.
Journal of Fluid Mechanics, 2012
In this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spher... more In this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spherical particles on which a torque is applied. Particles are mono-dispersed and neutrally buoyant. Since the torque modifies particle rotation, we show that it can indeed strongly change the effective viscosity of semi-dilute or even more concentrated suspensions. We perform our calculations up to a volume fraction of 28 %. And we compare our results to data obtained at 40 % by Yeo and Maxey (Phys. Rev. E, vol. 81, 2010, p. 62501) with a totally different numerical method. Depending on the torque orientation, one can increase (decrease) the rotation of the particles. This results in a strong enhancement (reduction) of the effective shear viscosity of the suspension. We construct a dimensionless number Theta\Theta Theta which represents the average relative angular velocity of the particles divided by the vorticity of the fluid generated by the shear flow. We show that the contribution of the parti...
et codirigée par Salima Rafaï préparée au sein du Laboratoire interdisciplinaire de Physique dans... more et codirigée par Salima Rafaï préparée au sein du Laboratoire interdisciplinaire de Physique dans Ecole Doctorale de Physique Locomotion et écoulements dans les fluides complexes confinés Thèse soutenue publiquement le 21 Octobre 2011, devant le jury composé de:
Cette these est consacree a l'etude de la dynamique et de la rheologie des fluides complexes.... more Cette these est consacree a l'etude de la dynamique et de la rheologie des fluides complexes. Nous utilisons une methode de simulation numerique a trois dimensions. Les systemes que nous etudions ici sont des suspensions de micro-nageurs actifs, des suspensions de particules spheriques rigides en presence d'un champ externe auquel elles sont sensibles et de la dynamique de suspensions de particules spheriques et confinees en cisaillement. Les Micro-nageurs sont les objets microscopiques qui se propulsent dans un fluide et ils sont omnipresents dans la nature. Un exemple commun de micro-nageurs est la micro-algue textit{Chlamydomonas} . Un des buts principaux de cette these est de comprendre l'effet de la motilite de ces micro-organismes sur les proprietes macroscopiques globales de la suspension, telles que la viscosite effective pour expliquer les observations experimentales. Nous avons elabore differents modeles de suspensions de textit{Chlamydomonas} et effectue des s...
Measuring quantitative and macroscopic parameters to estimate the global motility of a large popu... more Measuring quantitative and macroscopic parameters to estimate the global motility of a large population of swimming cells is a challenge. The rheology of suspensions containing such cells is a good solution to achieve such measurements. As a matter of fact, recent rheological measurements on suspensions of bacteria [1] or algae [2] have been performed very recently. These experiments showed the
Physical review. E, 2017
Micro-organisms usually can swim in their liquid environment by flagellar or ciliary beating. In ... more Micro-organisms usually can swim in their liquid environment by flagellar or ciliary beating. In this numerical work, we analyze the influence of flagellar beating on the orbits of a swimming cell in a shear flow. We also calculate the effect of the flagellar beating on the rheology of a dilute suspension of microswimmers. A three-dimensional model is proposed for Chlamydomonas Reinhardtii swimming with a breaststroke-like beating of two anterior flagella modeled by two counter-rotating fore beads. The active swimmer model reveals unusual angular orbits in a linear shear flow. Namely, the swimmer sustains orientations transiently across the flow. Such behavior is a result of the interplay between shear flow and the swimmer's periodic beating motion of flagella, which exert internal torques on the cell body. This peculiar behavior has some significant consequences on the rheological properties of the suspension. We calculate Einstein's viscosity of the suspension composed of ...
Physical Review Fluids, 2016
sphériques en présence d'un couple externe. Nous avons montré que le changement de vitesse angula... more sphériques en présence d'un couple externe. Nous avons montré que le changement de vitesse angulaire des particules due à l'application d'un couple externe est suisante pour modier fortement la viscosité de la suspension. Basée sur des simulations numériques, une formule semi-empirique a été proposée pour la viscosité des suspensions de particules sphériques valables jusqu'à 40% de concentration. Nous avons également montré que la 2ème loi de Faxén peut être étendue par une expression empirique pour de grandes concentrations.
Measuring quantitative and macroscopic parameters to estimate the global motility of a large popu... more Measuring quantitative and macroscopic parameters to estimate the global motility of a large population of swimming cells is a challenge. The rheology of suspensions containing such cells is a good solution to achieve such measurements. As a matter of fact, recent rheological measurements on suspensions of bacteria [1] or algae [2] have been performed very recently. These experiments showed the
Physical Review E, 2014
Three-dimensional (3D) numerical simulations are performed on suspensions composed of puller-like... more Three-dimensional (3D) numerical simulations are performed on suspensions composed of puller-like microswimmers that are sensitive to light (phototaxis) mimicking microalgae in a Poiseuille flow. Simulations are based on the numerical resolution of the flow equations at low Reynolds numbers discretized on a 3D grid (finite differences). The model reproduces the formation of a central jet of swimmers by self-focusing [Phys. Rev. Lett. 110, 138106 (2013)] but also predicts an instability of the jet, which leads to its fractionation in clusters. We show that this instability is due to hydrodynamic interactions between microswimmers, which attract each other along the flow direction. This effect was not observed in the experiments conducted on dilute suspensions (i.e., where hydrodynamic interactions are weak). This phenomenon is peculiar for pullers for which collective motions are usually not observed on such a time scale. With this modeling, we hope to pave the way toward a better understanding of concentration techniques of algae (a bottleneck challenge in industrial applications).
A three-dimensional model is proposed for Chlamydomonas Reinhardtii swimming with a breaststroke-... more A three-dimensional model is proposed for Chlamydomonas Reinhardtii swimming with a breaststroke-like beating of its two flagella. The model reveals unusual angular orbits of the active swimmer under a linear shear flow. Namely, the swimmer sustains orientation transiently across the flow when flagella plane is perpendicular to the shear plane, and amplify the shear-induced rotation along the flow. Such behavior is a result of the interplay between shear-induced deformation and swimmer's periodic beating motion that exerts internal torques on the torque-free swimmer. This particular behavior has some significant consequences on the rheological properties of the suspension that tends to confirm previous experimental results [Phys. Rev. Lett. 104, 098102 (2010)]. We calculated the intrinsic viscosity of the suspension with such isolated modeled microswimmers (dilute case) in shear flow using numerical simulations based on Rotne-Prager approximation. The results show an increased intrinsic viscosity for active swimmer suspensions in comparison to non-active ones in accordance with previous experimental measurements. A major enhancement of the active swimmer viscosity occurs due to the effectively extended shape of the deformable swimming cells. We also recover the experimentally observed shear thinning behavior.
Measuring quantitative and macroscopic parameters to estimate the global motility of a large popu... more Measuring quantitative and macroscopic parameters to estimate the global motility of a large population of swimming cells is a challenge. The rheology of suspensions containing such cells is a good solution to achieve such measurements. As a matter of fact, recent rheological measurements on suspensions of bacteria [1] or algae [2] have been performed very recently. These experiments showed the
Physical Review Letters, 2010
The measurement of a quantitative and macroscopic parameter to estimate the global motility of a ... more The measurement of a quantitative and macroscopic parameter to estimate the global motility of a large population of swimming biological cells is a challenge Experiments on the rheology of active suspensions have been performed. Effective viscosity of sheared suspensions of live unicellular motile micro-algae (Chlamydomonas Reinhardtii) is far greater than for suspensions containing the same volume fraction of dead cells and suspensions show shear thinning behaviour. We relate these macroscopic measurements to the orientation of individual swimming cells under flow and discuss our results in the light of several existing models.
Physical Review Letters, 2013
We study the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids i... more We study the dynamic self-assembly and propulsion of a ribbon formed from paramagnetic colloids in a dynamic magnetic field. The sedimented ribbon assembles due to time averaged dipolar interactions between the beads. The time dependence of the dipolar interactions together with hydrodynamic interactions cause a twisted ribbon conformation. Domain walls of high twist connect domains of nearly constant orientation and negligible twist and travel through the ribbon. The particular form of the domain walls can be controlled via the frequency and the eccentricity of the modulation. The flux of twist wallsa true ribbon property absent in slender bodies-provides the thrust onto the surrounding liquid that propels this biomimetic flagellum into the opposite direction. The propulsion efficiency increases with frequency and ceases abruptly at a critical frequency where the conformation changes discontinuously to a flat standing ribbon conformation.
Journal of Fluid Mechanics, 2012
In this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spher... more In this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spherical particles on which a torque is applied. Particles are mono-dispersed and neutrally buoyant. Since the torque modifies particle rotation, we show that it can indeed strongly change the effective viscosity of semi-dilute or even more concentrated suspensions. We perform our calculations up to a volume fraction of 28 %. And we compare our results to data obtained at 40 % by Yeo and Maxey (Phys. Rev. E, vol. 81, 2010, p. 62501) with a totally different numerical method. Depending on the torque orientation, one can increase (decrease) the rotation of the particles. This results in a strong enhancement (reduction) of the effective shear viscosity of the suspension. We construct a dimensionless number Theta\Theta Theta which represents the average relative angular velocity of the particles divided by the vorticity of the fluid generated by the shear flow. We show that the contribution of the parti...