Hiraku Nishimori

Collision Dynamics of Two Barchan Dunes Simulated Using a Simple Model

The collision processes of two crescentic dunes called barchans are systematically studied using a simple computer simulation model. The simulated processes, coalescence, ejection and reorganization, qualitatively correspond to those observed in a water tank experiment. Moreover we found the realized types of collision depend both on the mass ratio and on the lateral distance between barchans under initial conditions. A simple set of differential equations to describe the collision of one-dimensional (1D) dunes is introduced.

A simple model for the formation of vegetated dunes

A simple model for the dynamics of dunes associated with vegetation is proposed. Using the model, the formation processes of transverse dunes, parabolic dunes and elongated parabolic dunes are simulated according to two environmental factors: (i) the amount of sand at the source; (ii) the wind force. The results have qualitative correspondence to the real counterpart, and the simplicity of the algorithm and the consequent ease of handling this model provide us with wide applicability for the investigation of the complex interplay between vegetation and dunes. Copyright

AXIAL MIGRATION OF TWO SPECIES OF PARTICLES IN A HORIZONTAL CYLINDER

Axial segregation in a long horizontal rotating cylinder has generated much interest. Recent developments of the MRI (Magnetic Resonance Imaging) technology have given much needed insights into the dynamics as well as the internal structures of complex behavior. We have seen a number of axial segregation/mixing experiments and simulations but issues associated with the mechanism(s) of the axial segregation are still under investigation. In this paper we simply summarize axial migration phenomena that occur in an almost completely filled rotating cylinder.