Uncertainty of vibrated granular balls in dynamical behavior

Abstract There is a known granular motion pattern where a dense upper region is supported on a fluidized low-density region underneath, i.e., so-called density inversion which is regarded as a precursor to granular Leidenfrost effect1-2. In this work, we show another possible granular motion pattern by discrete element simulation, i.e., the granular wave-solid state3 which reflects the uncertainty of density inversion. The occurrence probability of density inversion or wave-solid state is presented by vibrating granular systems of random packing with constant excitation parameters. Moreover, our simulations further reproduce the well-known Butterfly effect that indicates the sensitivity of nonlinear systems to initial conditions. Based on the phenomena revealed by our simulations, we believe that density inversion which is highly influenced by initial packing state of granular balls is not the only path to granular Leidenfrost effect. In addition, we argue that the granular system that undergone one dynamic test is no longer the original one due to the change of granular packing state, which should not be ignored in the experimental studies of granular dynamics.