Granular Leidenfrost Effect Research Articles

Effect of excitation frequency on dissipation behavior of vibrated granular balls.

The dissipation behavior of granular balls in a quasi-2D vertically oscillating closed container is studied by the discrete element method with varying excitation frequencies in this work. Combining the dynamic behavior with dissipation effect of vibrated granular balls, the optimal damping effect of the phase transition critical stage between granular density inversion and granular Leidenfrost effect that involves four high damping granular phases (HDGPs) is revealed. Moreover, the high damping granular phases near and away from this phase transition critical stage are compared and analyzed further, which indicates the universal dynamic behavior of dense granular clusters playing the optimal damping effect. Finally, the optimal damping mechanism of granular balls in the quasi-2D closed container is clarified. Damping properties and motion states of partic.

Visual analysis of density and velocity profiles in dense 3D granular gases

Granular multiparticle ensembles are of interest from fundamental statistical viewpoints as well as for the understanding of collective processes in industry and in nature. Extraction of physical data from optical observations of three-dimensional (3D) granular ensembles poses considerable problems. Particle-based tracking is possible only at low volume fractions, not in clusters. We apply shadow-based and feature-tracking methods to analyze the dynamics of granular gases in a container with vibrating side walls under microgravity. In order to validate the reliability of these optical analysis methods, we perform numerical simulations of ensembles similar to the experiment. The simulation output is graphically rendered to mimic the experimentally obtained images. We validate the output of the optical analysis methods on the basis of this ground truth information. This approach provides insight in two interconnected problems: the confirmation of the accuracy of the simulations and the test of the applicability of the visual analysis. The proposed approach can be used for further investigations of dynamical properties of such media, including the granular Leidenfrost effect, granular cooling, and gas-clustering transitions.

Effect of the coefficient of restitution and friction in the granular Leidenfrost effect in the absence of gravity. A numerical study

In this study the granular Leidenfrost effect in the absence of gravity is investigated numerically by means of the discrete element method. Apart from identifying the phenomena, a parametric study to quantify the influence of the coefficient of restitution and friction in the packing fraction of the granular media is carried on numerically. Surprisingly, both the coefficient of restitution and the coefficient of friction exhibit an influence of the same magnitude in the packing fraction of the granular system, which has not been reported in experiments and simulation of granular Leidenfrost regime under gravity or microgravity conditions.

Granular Leidenfrost effect in microgravity

When a container filled with granular material is subjected to vertical vibration in the presence of gravity, under certain conditions a non-monotonous density profile can be observed. This effect which is characteristic for dissipative granular gases, was termed “floating cluster regime” or “granular Leidenfrost effect”. Here, we study the behavior of vibro-agitated granular matter in the absence of gravity and identify a corresponding stationary state of the granulate, that is, we provide experimental evidence of the granular Leidenfrost effect under conditions of weightlessness.

Experiments and characterization of low-frequency oscillations in a granular column.

The behavior of a vertically vibrated granular bed is reminiscent of a liquid in that it exhibits many phenomena such as convection and Faraday-like surface waves. However, when the lateral dimensions of the bed are confined such that a quasi-one-dimensional geometry is formed, the only phenomena that remain are bouncing bed and the granular Leidenfrost effect. This permits the observation of the granular Leidenfrost state for a wide range of energy injection parameters and more specifically allows for a thorough characterization of the low-frequency oscillation (LFO) that is present in this state. In both experiments and particle simulations we determine the LFO frequency from the power spectral density of the center-of-mass signal of the grains, varying the amplitude and frequency of the driving, the particle diameter, and the number of layers in the system. We thus find that the LFO frequency (i) is inversely proportional to the fast inertial timescale and (ii) decorrelates with a typical decay time proportional to the slow dissipative timescale in the system. The latter is consistent with the view that the LFO is driven by the inherent noise that is present in the granular Leidenfrost state with a low number of particles.

Damping behaviors of granular particles in a vertically vibrated closed container

Damping behaviors of granular particles in a quasi-two-dimensional (Q-2D) closed container subjected to vertical vibration are simulated by means of Discrete Element Method (DEM). Phase diagram and damping contour of vibrated granular particles in the amplitude-frequency plane of external excitation are obtained, which indicates six different damping phases of vibrated granular particles. Simulation results also reveal that three suspended states of vibrated granular particles (i.e., Leidenfrost effect, Buoyancy convection and Bidirectional Leidenfrost effect) display the higher damping capacity, and especially granular Leidenfrost effect demonstrates the optimal damping effect. Furthermore, the dissipation characteristic of granular Leidenfrost effect is analyzed respectively from the perspective of energy transformation and energy dissipation. The influence of the corresponding parameters (gap clearance, particle diameter and container dimension) on the three high damping suspended phases (HDSPs) of vibrated granular particles is explored. Finally, base on the rheological behavior of vibrated granular particles, a visualization method for evaluating the granular damping effect by DEM simulation is proposed for the first time, which may provide a new idea for designing optimal granular dampers.

Noise induces rare events in granular media.

The granular Leidenfrost effect [B. Meerson, et al., Phys. Rev. Lett. 91, 024301 (2003)PRLTAO0031-900710.1103/PhysRevLett.91.024301; P. Eshuis et al., Phys. Rev. Lett. 95, 258001 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.258001] is the levitation of a mass of granular matter when a wall below the grains is vibrated, giving rise to a hot granular gas below the cluster. We find by simulation that for a range of parameters the system is bistable: the levitated cluster can occasionally break and give rise to two clusters and a hot granular gas above and below. We use techniques from the theory of rare events to compute the mean transition time for breaking to occur. This requires the introduction of a two-component reaction coordinate.

Motion mode of the optimal damping particle in particle dampers

To explore the optimal damping mechanism of Particle dampers (PDs), experimental studies on the relationship between the optimal damping performance of PDs and the motion mode of damping particles in PDs were conducted. First, the damping performance of PDs under a certain initial condition was investigated via cantilever system experiments. Then a simple evaluation of the effective mass and effective damping of PDs was performed by fitting the experimental data to an equivalent Single-degree-of-freedom (SDOF) system without damping particles. Finally, the motion mode of damping particles playing the optimal damping effect was determined by vibration table tests with the corresponding control parameters used in the cantilever system experiments. The study results indicate that when the optimal damping performance of PDs is obtained, the granular Leidenfrost effect, whereby the entire damping particle bed is levitated above the vibrating base by a layer of highly energetic particles, is observed in PDs. The optimal damping performance of PDs is mainly caused by the dissipative properties of damping particles in Leidenfrost state.

Rheology behavior and optimal damping effect of granular particles in a non-obstructive particle damper

To explore the optimal damping mechanism of non-obstructive particle dampers (NOPDs), research on the relationship between the damping performance of NOPDs and the motion mode of damping particles in NOPDs was carried out based on the rheological properties of vibrated granular particles. Firstly, the damping performance of NOPDs under different excitation intensity and gap clearance was investigated via cantilever system experiments, and an approximate evaluation of the effective mass and effective damping of NOPDs was performed by fitting the experimental data to an equivalent single-degree-of-freedom (SDOF) system with no damping particles. Then the phase diagrams which could show the motion mode of damping particles under different excitation intensity and gap clearance were obtained via a series of vibration table tests. Moreover, the dissipation characteristic of damping particles was explored by the discrete element method (DEM). The study results indicate that when NOPDs play the optimal damping effect the granular Leidenfrost effect whereby the entire particle bed in NOPDs is levitated above the vibrating base by a layer of highly energetic particles is observed. Finally, the damping characteristics of NOPDs was explained by collisions and frictions between particle–particle and particle–wall based on the rheology behavior of damping particles and a new dissipation mechanism was first proposed for the optimal damping performance of NOPDs.

Electrical capacitance sensor array to measure density profiles of a vibrated granular bed

Monitoring the dynamical evolution of the solids distribution within vibrating granular beds is of key importance to control a variety of industrial processes and to assist basic studies on phenomena like segregation and convection. One of the most used techniques is video analysis, however it is restricted to quasi-two dimensional beds and may need considerable postprocessing time. Here we explore an alternative technique based on a simple linear capacitor array that is able to resolve variations of the solid fraction along a single direction. This method has potential to be used in real-time control applications due to the simple signal processing needed and it’s suited to probe three dimensional beds. We show a comparison between spatiotemporal density profiles of a quasi two dimensional vertically vibrated bed obtained with video and capacitive methods, and discuss on the advantages and downsides of each one. We also present spatiotemporal density profiles of a three dimensional vertically vibrated bed using the capacitive technique, illustrating the distribution of material along the direction of vibration when the bed performs bouncing motion and when the forcing is enough to obtain a granular Leidenfrost effect.

Granular Leidenfrost effect in vibrated beds with bumpy surfaces

The effects of subjecting a bed of granular materials to horizontal vibrations by a bumpy oscillating surface have been investigated computationally in this study. The behaviour of the granular bed is determined by the vibration conditions applied which include the vibrating frequency and amplitude as well as the bumpiness of the oscillating surface. Under sufficiently vigorous vibration conditions, the granular Leidenfrost effect whereby the entire granular bed is levitated above the vibrating base by a layer of highly energetic particles may be observed. Granular temperature profiles of systems that exhibit the granular Leidenfrost effect indicate an unequal distribution of energy between particles near the vibrating base and those in the bulk. A bumpy oscillating surface was also observed to be more effective at introducing perturbations and transferring energy into a granular bed. The granular Leidenfrost effect can be induced by the application of larger grain sizes of particles constituting the bumpy vibrating base under vibration conditions that are normally insufficient for the onset of the effect. Lastly, a phase diagram which can be utilized for predicting the behaviours of granular beds that are subjected to oscillations by various types of bumpy surfaces has been constructed based on the simulation results obtained.

Onset of Convection in Strongly Shaken Granular Matter

Strongly vertically shaken granular matter can display a density inversion: A high-density cluster of beads is elevated by a dilute gaslike layer of fast beads underneath ("granular Leidenfrost effect"). For even stronger shaking the granular Leidenfrost state becomes unstable and granular convection rolls emerge. This transition resembles the classical onset of convection in fluid heated from below at some critical Rayleigh number. The same transition is seen in molecular dynamics (MD) simulations of the shaken granular material. The critical shaking strength for the onset of granular convection can be calculated from a linear stability analysis of a hydrodynamiclike model of the granular flow. Experiment, MD simulations, and theory quantitatively agree.

Phase diagram of vertically shaken granular matter

A shallow, vertically shaken granular bed in a quasi-two-dimensional container is explored experimentally yielding a wider variety of phenomena than in any previous study: (1) bouncing bed, (2) undulations, (3) granular Leidenfrost effect, (4) convection rolls, and (5) granular gas. These phenomena and the transitions among them are characterized by dimensionless control parameters and combined in a full experimental phase diagram.

Granular Leidenfrost Effect: Experiment and Theory of Floating Particle Clusters

Granular material is vertically vibrated in a 2D container: above a critical shaking strength, and for a sufficient number of beads, a crystalline cluster is elevated and supported by a dilute gaseous layer of fast beads underneath. We call this phenomenon the granular Leidenfrost effect. The experimental observations are explained by a hydrodynamic model featuring three dimensionless control parameters: the energy input S, the number of particle layers F, and the inelasticity of the particle collisions epsilon. The (S,F) phase diagram, in which the Leidenfrost state lies between the purely solid and gas phases, shows accurate agreement between experiment and theory.