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 0 < Gamma(h,v) < 1.6. Phenomena include th e spontaneous formation of a static heap at Gamma(hs)(Gamma(v)) when G amma(v) < 1, convective flow for Gamma(hc) > Gamma(hs), and a novel sw itching state for frequencies omega(v) not equal omega(h). A simple fr iction model provides an approximate, but not exact, description of th e steady states and the transition to convection. [S0031-9007(98)06699 -X].