| Granular materials exhibit bulk properties that are distinct from conventional solids, liq- uids, and gases, due to the dissipative nature of the inter-granular forces. Understanding the fundamentals of granular materials draws upon and gives insight into many fields at the current frontiers of physics, such as plasticity of solids, fracture and friction, com- plex systems such as colloids, foams and suspensions, and a variety of biological systems. Particulate flows are widespread in geophysics, and are also essential to many industries. Despite the importance of these phenomena, we lack a theoretical model that explains most behaviors of granular materials. Since granular assemblies are highly dissipative, they are often far from mechanical equilibrium, making most classical analyses inappli- cable. A theory for dilute granular systems exists, but for dense granular systems (by far the majority of granular systems in the real world) no comparable theory is accepted.;We approach this problem by examining the fluidization, or transition from solid to liquid, in dense granular systems. In this study, the separate effects of random noise and vibration on the static to flowing transition of a dense granular assembly under planar shear is studied numerically using soft contact particle dynamics simulations in two dimensions. We focus on small systems in a thin planar Couette cell, examining the bistable region while increasing shear, with varying amounts of random noise or vibration, and determine the statistics of the shear required for the onset of flow. We find that the applied power is the key parameter in determining the magnitude of the effects of the noise or vibration, with vibration frequency also having an influence. Similarities and differences between noise and vibration are determined, and the results compare favorably with a two phase model for dense granular flow. |
