Gerald H. Ristow

BOUNDARY EFFECTS ON THE ANGLE OF REPOSE IN ROTATING CYLINDERS

The angle of repose for the flow of granular materials in a half-filled rotating drum is studied by means of experiments and computer simulations. Particles of different material properties are used to investigate the effects of the end caps on the angle of repose. By fitting the numerical results to an exponentially decaying function, we are able to calculate the characteristic range

COMPETITION OF MIXING AND SEGREGATION IN ROTATING CYLINDERS

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Forces on the walls and stagnation zones in a hopper filled with granular material

of the influence of the wall. We found that

On The Application Of A Novel Algorithm To Hydrodynamic Diffusion And Velocity Fluctuations In Sedimenting Systems

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MOLECULAR DYNAMICS SIMULATIONS OF GRANULAR MATERIALS ON THE INTEL iPSC/860

scales with the drum radius but does not depend on either the density or the gravitational constant. For increasing particle diameter, finite size effects are visible.

Particles moving in spatially bounded, viscous fluids

Using discrete element methods, we study numerically the dynamics of the size segregation process of binary particle mixtures in three-dimensional rotating drums, operated in the continuous flow regime. Particle rotations are included and we focus on different volume filling fractions of the drum to study the interplay between the competing phenomena of mixing and segregation. It is found that segregation is best for a more than half-filled drum due to the nonzero width of the fluidized layer. For different particle size ratios, it is found that radial segregation occurs for any arbitrary small particle size difference and the final amount of segregation shows a linear dependence on the size ratio of the two particle species. To quantify the interplay between segregation and mixing, we investigate the dynamics of the center of mass positions for each particle component. Starting with initially separated particle groups we find that no mixing of the component is necessary in order to obtain a radially segregated core.

Size Segragation of Granular Materials in a 3D Rotating Drum

We measure the pressure and the shear forces acting on the walls of an outflowing hopper using Molecular Dynamics simulations. We find very strong fluctuations which for large opening angles follow a power spectrum but have white noise for smaller angles. We also calculate the shape of the stagnation zones that appear during funnel flow and compare it to the experimentally observed ones.

Density waves in granular flow

We present a numerical method to deal efficiently with large numbers of particles in incompressible fluids. The interactions between particles and fluid are taken into account by a physically motivated ansatz based on locally defined drag forces. We demonstrate the validity of our approach by performing numerical simulations of sedimenting non-Brownian spheres in two spatial dimensions and compare our results with experiments. Our method reproduces qualitatively important aspects of the experimental findings, in particular the strong anisotropy of the hydrodynamic bulk self-diffusivities.

Formation of Patterns in Granular Materials

In this paper we present an efficient algorithm to perform Molecular Dynamics simulations on a distributed memory parallel computer, the Intel iPSC/860. The proposed model describes the flow properties of granular materials in two dimensions. The specific implementation on a 32 node iPSC/860, especially the message passing and load balancing algorithms, are discussed in detail. Performance data are shown for different computers and varying node numbers of the iPSC/860. As a physical example we calculate some properties of the outflow behavior from a two-dimensional hopper and we discuss possible extensions of our model to three dimensions. Our simulations show that Molecular Dynamics simulations can be implemented quite efficiently on a distributed memory parallel computer if one assures load balancing and optimizes the internode communications.

AN ITERATIVE NONUNIFORMLY SPACED FINITE DIFFERENCE SCHEME FOR COMPUTATIONAL FLUID DYNAMICS

Abstract Using finite difference methods, we study the dynamics of a single spherical object in a two-dimensional box filled with viscous fluid under the influence of gravity. The algorithm is validated using experimental and analytic results. Special emphasis is made on the implementation and performance of two different algorithms on the parallel computer Cray-T3D. Parallel versions of the codes were tested for their speedups and the numbers are analyzed and explained to discuss further improvements.