Hisao Hayakawa

Collisional granular flow as a micropolar fluid.

We show that a micropolar fluid model successfully describes collisional granular flows on a slope. A micropolar fluid is the fluid with internal structures in which coupling between the spin of each particle and the macroscopic velocity field is taken into account. It is a hydrodynamical framework suitable for granular systems which consists of particles with macroscopic size. We demonstrate that the model equations can quantitatively reproduce the velocity and the angular velocity profiles obtained from the numerical simulation of the collisional granular flow on a slope using a simple estimate for the parameters in the theory.

Critical scaling near jamming transition for frictional granular particles.

The critical rheology of sheared frictional granular materials near jamming transition is numerically investigated. It is confirmed that there exists a true critical density which characterizes the onset of the yield stress and two fictitious critical densities which characterize the scaling laws of rheological properties. We find the existence of a hysteresis loop between two of the critical densities for each friction coefficient. It is noteworthy that the critical scaling law for frictionless jamming transition seems to be still valid even for frictional jamming despite using fictitious critical density values.

Dynamical simulation of fluidized beds: Hydrodynamically interacting granular particles

A numerical simulation of a gas-fluidized bed is performed without introduction of any empirical parameters. Realistic bubbles and slugs are observed in our simulation. It is found that the convective motion of particles is important for the bubbling phase and there is no convection in the slugging phase. From the simulation results, non-Gaussian distributions are found in the particle velocities and the relation between the deviation from Gaussian and the local density of particles is suggested. It is also shown that the power spectra of particle velocities obey power laws. A brief explanation of the relationship between the simulation results and the Kolmogorov scaling argument is discussed.

4/3 LAW OF GRANULAR PARTICLES FLOWING THROUGH A VERTICAL PIPE

Density waves of granular material (sand) flowing through a vertical pipe have been investigated. Clear density waves emerge when the cock attached to bottom end of the pipe is closed. The FFT power spectra were found to show a stable power-law form

Geometrical expression of excess entropy production.

P(f) \sim f^{-\alpha}.

Hydrodynamic description of granular convection.

The value of the exponent was evaluated as

Synchronization of kinks in the two-lane totally asymmetric simple exclusion process with open boundary conditions

\alpha \cong 4/3

Stochastic energetics for non-Gaussian processes.

. We also introduce a simple one-dimensional model which reproduces

Size distribution of particles in Saturn’s rings from aggregation and fragmentation

\alpha = 4/3

Negative Normal Restitution Coefficient Found in Simulation of Nanocluster Collisions

from both simulation and theoretical analysis. (to be published in Phys.Rev.Lett.)