Numerical investigations of the effect of friction and vibrational amplitude on convection phenomena in granular materials under vertical vibrations

This study investigates the effects of wall friction coefficient (μw), interparticle friction coefficient (μp) and vibrational amplitude on convection phenomena occurring in two-dimensional granular systems under vertical vibration. Non-smooth contact dynamics method was used for that purpose. Various values of μw and μp between 0.1 and 1.0 were tested. Monodisperse-like granular samples composed of 4000 disks were subjected to vertical vibration with a dimensionless vibrational acceleration of 5, while vibrational amplitudes of 0.35D, 0.5D and 1.0D were applied (where D is a mean disk diameter). A new indicator for describing the strength and direction of the convection is proposed to analyze the simulation results: the dimensionless angular velocity W. It was found that the non-convection occurs when μw < 0.3 or μp < 0.2. However, the single-layer convection begins to appear when μw ≥ 0.3 and μp ≥ 0.2. Then, single-layer convection evolves into multi-layer convection as both frictions increase. Moreover, the strength of convection increases rapidly with μp, reaching its maximum value when μp = μw. The convection strength then appears to stabilize with small fluctuations. In addition, the vibrational amplitude appears to significantly affect the convection strength in the case where μp and μw are greater than 0.6.