Waves and oscillations on vertically-vibrated separated binary systems
Abstract: When fine granular particulates are vertically vibrated within a fluid at low frequencies, the granular bed may break symmetry and exhibit Faraday tilting. Vertically vibrated binary mixtures of bronze and glass spheres will separate into regions rich in glass and regions rich in bronze. At low frequencies, a single bronze region will form above a single glass region. This system too shows tilting. We will describe two situations in which the resulting configuration is not stable. In a rectangular container, the granular system may oscillate backwards and forwards between two equivalent tilted forms, with a period dependent upon the driving conditions. Within two concentric cylinders, this instability results in continuous travelling wave motion. The common mechanism behind these behaviours is described.