Growth of force chain network upon non-Bagnold Transition of Inclined Surface Granular Flows via Discrete Element Simulation

Abstract A steady granular flow down an inclined surface is an important flow configuration to study the dynamic of dry granular flow. This work adopts two-dimensional discrete element simulation to study how inter-grain friction may play a role in momentum transport, in addition to the collision-based transport, to induce the non-Bagnold flow velocity profile reported in the literature. Special efforts were made to apply the knowledge of network science to identify the contact force chain network from particle dynamics information using the graph theory with the Louvain greedy algorithm. We studied how the number of grains born in the force chain network grows when the flow scaled velocity profile degrades from Bagnold to non-Bagnold flows. Concurrently, the stress loading ratio carried by these frictional contacts rises abruptly upon the non-Bagnold flow transition identifies when the flow Froude number falls roughly below 2.15. Both phenomena suggest that the non-local phenomenon of Bagnold velocity profile degradation occurs when sufficient grains are confined in the force chain network to assist the stress transport, replacing the collisional transport. Hence, a refined rheology model is needed in the future to account for this friction-assisted momentum transport at a mesoscopic yet flow-dependent length scale like that of the currently investigated force network.