Vertical and Horizontal Vibration of Granular Materials: Coulomb Friction and a Novel Switching State

Experiments for simultaneous horizontal (h) and vertical (v) vibration of granular materials show novel flow dynamics. We focus on moderate dimensionless accelerations 0₇ₒ, and a novel switching state for frequencies ₕ₇. A simple friction model provides an approximate, but not exact, description of the steady states and the transition to convection.