References of "Opsomer, Eric"
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See detailSmall solar system bodies as granular systems
Hestroffer, Daniel; Campo Bagatin, Adriano; Losert, Wolfgang et al

in EPJ Web of Conferences (2017, June 30)

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See detailVibration Induced Phenomena in Granular Media in Microgravity
Opsomer, Eric ULg; Noirhomme, Martial ULg; Vandewalle, Nicolas ULg

in EPJ Web of Conferences (2017, June 30)

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See detailFrustrated crystallization of a monolayer of magnetized beads under geometrical confinement
Schockmel, Julien ULg; Vandewalle, Nicolas ULg; Opsomer, Eric ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2017)

We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short ... [more ▼]

We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short range magnetic dipole-dipole potential induced by an external magnetic field. The grains are confined by repulsing walls and are homogeneously distributed inside the cell. A two-dimensional (2d) Brownian motion is induced by horizontal mechanical vibrations. Therefore, the balance between magnetic interaction and agitation allows investigating 2d phases through direct visualization. The effect of both confinement size and shape on the grains’ organization in the low-energy state has been investigated. Concerning the confinement shape, triangular, square, pentagonal, hexagonal, heptagonal, and circular geometries have been considered. The grain organization was analyzed after a slow cooling process. Through the measurement of the averaged bond order parameter for the different confinement geometries, it has been shown that cell geometry strongly affects the ordering of the system. Moreover, many kinds of defects, whose observation rate is linked to the geometry, have been observed: disclinations, dislocations, defects chain, and also more exotic defects such as a rosette. Finally, the influence of confinement size has been investigated and we point out that no finite-size effect occurs for a hexagonal cell, but the finite-size effect changes from one geometry to another. [less ▲]

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See detailCoarsening dynamics of a granular lattice gas
Opsomer, Eric ULg; Noirhomme, Martial ULg; Ludewig, François et al

Poster (2017, March 23)

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See detailCluster growth in driven granular gases
Noirhomme, Martial ULg; Ludewig, François; Vandewalle, Nicolas ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2017)

We investigate numerically and theoretically the internal structures of a driven granular gas in cuboidal cell geometries. Clustering is reported and particles are classified as gaseous or clustered via a ... [more ▼]

We investigate numerically and theoretically the internal structures of a driven granular gas in cuboidal cell geometries. Clustering is reported and particles are classified as gaseous or clustered via a local packing fraction criterion based on a Voronoi tessellation. We observe that small clusters arise in the corners of the box, elucidating early reports of partial clustering. These aggregates have a condensation-like surface growth. When a critical size is reached, a structural transition occurs and all clusters merge together, leaving a hole in the center of the cell. This hole then becomes the new center of particle capture. Taking into account all structural modifications and defining a saturation packing fraction, we propose an empirical model for the cluster growth. [less ▲]

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See detailSegregation and pattern formation in dilute granular media under microgravity conditions
Opsomer, Eric ULg; Noirhomme, Martial ULg; Vandewalle, Nicolas ULg et al

in NPJ Microgravity (2017), 3

Space exploration and exploitation face a major challenge: the handling of granular materials in low-gravity environments. Indeed, grains behave quite differently in space than on Earth, and the ... [more ▼]

Space exploration and exploitation face a major challenge: the handling of granular materials in low-gravity environments. Indeed, grains behave quite differently in space than on Earth, and the dissipative nature of the collisions between solid particles leads to clustering. Within poly-disperse materials, the question of segregation is highly relevant but has not been addressed so far in microgravity. From parabolic flight experiments on dilute binary granular media, we show that clustering can trigger a segregation mechanism, and we observe, for the first time, the formation of layered structures in the bulk. [less ▲]

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See detailNovel structures for optimal space partitions
Opsomer, Eric ULg; Vandewalle, Nicolas ULg

in New Journal of Physics (2016)

Partitioning space into polyhedra with a minimum total surface area is a fundamental question in science and mathematics. In 1887, Lord Kelvin conjectured that the optimal partition of space is obtained ... [more ▼]

Partitioning space into polyhedra with a minimum total surface area is a fundamental question in science and mathematics. In 1887, Lord Kelvin conjectured that the optimal partition of space is obtained with a 14-faced space-filling polyhedron, called tetrakaidecahedron. Kelvin’s conjecture resisted a century until Weaire and Phelan proposed in 1994 a new structure, made of eight polyhedra, obtained from numerical simulations. Herein, we propose a stochastic method for finding efficient polyhedral structures, maximizing the mean isoperimeter Q, instead of minimizing total area. We show that novel optimal structures emerge with non-equal cell volumes and uncurved facets. A partition made of 24 polyhedra, is found to surpass the previous known structures. Our work suggests that other structures with high isoperimeter values are still to be discovered in the pursuit of optimal space partitions. [less ▲]

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See detailCoarsening dynamics of a granular lattice gas
Opsomer, Eric ULg; Noirhomme, Martial ULg; Ludewig, François et al

Poster (2016, July 22)

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See detailOn the coarsening dynamics of a granular lattice gas
Opsomer, Eric ULg; Noirhomme, Martial ULg; Ludewig, François et al

in European Physical Journal E -- Soft Matter (2016)

We investigated experimentally and theoretically the dynamics of a driven granular gas on a square lattice and discovered two characteristic regimes: Initially, given the dissipative nature of the ... [more ▼]

We investigated experimentally and theoretically the dynamics of a driven granular gas on a square lattice and discovered two characteristic regimes: Initially, given the dissipative nature of the collisions, particles move erratically through the system and start to gather on selected sites called traps. Later on, the formation of those traps leads to a strong decrease of the grain mobility and slows down dramatically the dynamics of the entire system. We realize detailed measurements linking a trap’s stability to the global evolution of the system and propose a model reproducing the entire dynamics of the system. Our work emphasizes the complexity of coarsening dynamics of dilute granular systems. [less ▲]

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See detailClustering and segregation in a driven bi-disperse granular gas
Opsomer, Eric ULg; Ludewig, François; Vandewalle, Nicolas ULg

Conference (2015, September 24)

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See detailGathering and handling of granular materials under microgravity conditions
Opsomer, Eric ULg; Ludewig, François; Noirhomme, Martial ULg et al

Conference (2015, March 27)

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See detailGranular transport in driven granular gas
Noirhomme, Martial ULg; Opsomer, Eric ULg; Ludewig, François ULg et al

in European Physical Journal E -- Soft Matter (2015), 38

We numerically and theoretically investigate the behavior of a granular gas driven by asymmetric plates. The injection of energy in the dissipative system differs from one side to the opposite one. We ... [more ▼]

We numerically and theoretically investigate the behavior of a granular gas driven by asymmetric plates. The injection of energy in the dissipative system differs from one side to the opposite one. We prove that the dynamical clustering which is expected for such a system is affected by the asymmetry. As a consequence, the cluster position can be fully controlled. This property could lead to various applications in the handling of granular materials in low-gravity environment. Moreover, the dynamical cluster is characterized by natural oscillations which are also captured by a model. These oscillations are mainly related to the cluster size, thus providing an original way to probe the clustering behavior. [less ▲]

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See detailGathering and Handling of Granular Materials under Microgravity Conditions
Opsomer, Eric ULg

Doctoral thesis (2014)

When a granular material is driven in microgravity environment, one can assist to the formation of dense and slow regions in the system. Indeed, given the dissipative character of the collisions in the ... [more ▼]

When a granular material is driven in microgravity environment, one can assist to the formation of dense and slow regions in the system. Indeed, given the dissipative character of the collisions in the media, energy is lost at each particle interaction and the grains begin to clump locally. The phenomenon has been observed for the first time in the late nineties during sounding rocket experimentation by Falcon and his coworkers and has attracted the interest of many scientists since then. However, precise laws describing the formation and the dynamics of such clusters are still lacking. In order to allow an intensive study of the phenomenon, the European Space Agency set up the SpaceGrains project. Small bronze spheres are enclosed in a rectangular cell and vertically driven by to pistons oscillating in phase opposition. Our work consists in the preparation of the SpaceGrains experiment via molecular dynamics simulations and the elaboration of models predicting the behaviour of the system. Before we started our study concerning SpaceGrains, we reproduced and extended Falcon’s sounding rocket experiments. We showed that, in addition to the granular gas and the cluster, another dynamical regime can be observed in the system. Indeed, for higher filling fractions, the entire granular media behaves like one single completely dissipative particle called the bouncing aggregate. Bouncing modes are observed and can be explained considering the bouncing ball paradigm. Moreover, we highlighted the role of the packing fraction φ as well as the size of the particles R on the different observed dynamics. Within the frame of the SpaceGrains device, we studied the impact of all tunable parameters of the experiment on the dynamics of the system. Thanks to an appropriate scaling all transition points that we obtained by varying the driving amplitude A, the packing fraction and the dimen- sions of the cell L fall along a same theoretical curve. The latter is explained regarding the energy transfer from the piston towards the center of the cell. Once the clustering was controlled, we investigated the handling of the agglomerate. By compartmentalizing the container, local trapping can be achieved and a granular pendant of Maxwell’s demon can be observed in microgravity. Based on the measured particle flux between the compartments, we realized a theoretical model predicting the asymptotic steady state of the system depending on the total number N of particles. In a clustered system, we investigated the impact of asymmetrical driving on the system’s dy- namics. We showed that the mean position of the cluster can be fully controlled via the amplitude ratio a. Moreover, the natural fluctuations of the agglomerate around its equilibrium position are dictated by the driving frequency f and the mass of the cluster. Finally, we realized simulations of driven bi-disperse gases and investigated the segregation phenomena in the system. We showed that clustering and segregation are strongly linked and that the size and the mass of the particles impact the segregation dynamics in different ways. [less ▲]

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See detailClustering and segregation in driven granular fluids
Opsomer, Eric ULg; Vandewalle, Nicolas ULg; Noirhomme, Martial ULg et al

in European Physical Journal E -- Soft Matter (2014)

In microgravity, the successive inelastic collisions in a granular gas can lead to a dynamical clustering of the particles. This transition depends on the filling fraction of the system, the restitution ... [more ▼]

In microgravity, the successive inelastic collisions in a granular gas can lead to a dynamical clustering of the particles. This transition depends on the filling fraction of the system, the restitution of the used materials and on the size of the particles. We report simulations of driven bi-disperse gas made of small and large spheres. The size as well as the mass difference imply a strong modification in the kinematic chain of collisions and therefore alter significantly the formation of a cluster. Moreover, the different dynamical behaviors can also lead to a demixing of the system, adding a few small particles in a gas of large ones can lead to a partial clustering of the taller type. We realized a detailed phase diagram recovering the encountered regimes and developed a theoretical model predicting the possibility of dynamical clustering in binary systems. [less ▲]

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See detailClustering et ségrégation dans les gaz granulaires bi-disperses
Opsomer, Eric ULg; Ludewig, François; Vandewalle, Nicolas ULg

Poster (2014, March 17)

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See detailHow dynamical clustering triggers Maxwell's demon in microgravity
Opsomer, Eric ULg; Noirhomme, Martial ULg; Vandewalle, Nicolas ULg et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2013), 88

In microgravity, the gathering of granular material can be achieved by a dynamical clustering whose existence depends on the geometry of the cell that contains the particles and the energy that is ... [more ▼]

In microgravity, the gathering of granular material can be achieved by a dynamical clustering whose existence depends on the geometry of the cell that contains the particles and the energy that is injected into the system. By compartmentalizing the cell in several subcells of smaller volume, local clustering is triggered and the so formed dense regions act as stable traps. In this paper, molecular dynamics simulations were performed in order to reproduce the phenomenon and to analyze the formation and the stability of such traps. Depending on the total number N of particles present in the whole system, several clustering modes are encountered and a corresponding bifurcation diagram is presented. Moreover, an iterative model based on the measured particle flux F as well as a theoretical model giving the asymptotical steady states are used to validate our results. The obtained results are promising and can provide ways to manipulate grains in microgravity. [less ▲]

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See detailPhase Transitions in Driven Granular Systems under Microgravity Conditions
Opsomer, Eric ULg; Ludewig, François; Vandewalle, Nicolas ULg

Conference (2013, July)

Detailed reference viewed: 13 (2 ULg)