HR: 0830h
AN: V51F-0345    [PDF]
TI: Numerical study of segregation mechanism in granular flow on inclined rough surface
AU: * Mitani, N K
EM: mitani@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Matuttis, H
EM: hg@miyazaki.mce.uec.ac.jp
AF: Department of Intelligent Systems and Mechanical Engineering, University of Electro-Communications, Chofugaoka 1-5-1, Chofu, Tokyo, 182-8585 Japan
AU: Kadono, T
EM: kadono@gaea.k.u-tokyo.ac.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Marine Science and Technology Center, Natsushima 2-15, Yokosuka, Kanagawa, 237-0061 Japan
AB: Pyroclastic flow deposits commonly consist of several vertical layers: a reversely graded fine-grained basal ash layer, and a massive main body in which pumice clasts are reversely graded while lithic clasts are normally graded. Most of these structures are thought to be formed during transport processes. Previously, experiments have shown that the normally graded structures can be formed by gas fluidization or hindered-settling. However, pyroclastic flows accompanied by lateral motion on inclined surface with significant velocity shears are dissimilar to both those experiments performed in stationary tanks. Numerical and experimental studies on high-concentration granular flow show that the degree of the shear is important in reversely graded segregation. Other numerical studies show that granular flows are affected by the roughness of ground surface. Additionally, using a classical granular theory implying that the collisions are dominant and the grain concentration is dilute, it is shown that the grain-dispersive pressure induced by the shear is important in the formation of the layer structures. In this study, we numerically analyze the inner structure of granular flows and clarify the relationships between the reversely-graded segregation mechanism depending on the inclination and the roughness of the ground, and the ratios of size and number densities of large and small grains. Simulations are performed using a two-dimensional Discrete Element Method. Since the density is high, we adopt the soft particle method that allows us to treat multi-body collisions. We adopt periodic boundary in order to calculate processes which occur over a long distance. Furthermore, we use a rough ground. Numerical results show that the velocity and number density of grains form layer structures and the number density becomes low near the base as previous studies show. This is because the gravity energy is converted into random kinetic energy (granular temperature) due to the velocity shear that is largest near the ground. As the inclination or the roughness of the ground increases, the granular temperature increases because of the increase of the shear velocity. The granular temperature plays an important role for reversely-graded segregation. In the large granular temperature, there are spaces for small particles to drop under large particles. As the inclination and the degree of the roughness increase, this dynamic sieving effect becomes greater.
DE: 3220 Nonlinear dynamics
DE: 8400 VOLCANOLOGY
DE: 8404 Ash deposits
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting