Simulation Of Dynamic Response Characteristics Of Granular Materials By Discrete Element Method

Granular materials are widely existed in nature and industrial processes.The related unit operation devices include moving bed,blast furnace and other reactors,mixing devices such as roller,ball mill,hopper,transportation pipeline and other transportation devices.A typical feature of dense granular materials is that the internal stress distribution is extremely uneven,and a few particles bear most of the external load.One of the direct consequences of the non-uniformity of the stress distribution is that the dynamic response characteristics of particles show a strong spatiotemporal correlation.Therefore,it is of great significance to understand the statistical properties and the underlying mechanisms of mechanical response granular materials from the component particle scale.Focusing on the mechanical response of a tagged particle inside a dense granular material,in this work the movement of an intruder inside a 2D granular system dragged either with constant velocity or by a spring was investigated by performing discrete element method(DEM)simulations.The variations of force experienced by the intruder and also the evolutions of the force chain network were systematically investigated by considering a number of key parameters.The main work of this paper is as follows:(1)Under the condition of constant velocity traction,the horizontal traction force is related to the traction speed: For low traction velocity,the traction force is nearly constant and independent on the traction velocity,and the interaction between the dragged intruder and its neighbor particles is mainly the enduring contact;for large traction velocity,the traction force increases linearly with the traction velocity.At the time,the interaction between the dragged intruder and its neighbor particles is mainly in the form of instantaneous collision.(2)The force experienced by the dragged intruder is closely related to its size and also the frictional properties of particles.The drag force increases with intruder size.Analyses indicate that this can be attributed to the fact that the number of particles dragged by the intruder increases linearly with intruder size.Increasing particle frictional coefficient lead to the increase of drag force.This can be ascribed to the fact that increasing frictional coefficient is helpful to strengthen the stability of force chain,thus intensify the resistance experienced by the intruder.Mesoscopic-scale analyses demonstrate that the topology of force chain network in front of the intruder can notably influence the force experienced by the intruder.Longer and straighter force chains with more branches will lead to larger drag force.(3)Analyses of the stick-slip events occurred during the spring traction process show that the slip event is the macroscopic reflection of the accumulating slip movements of particles during the stick period.It is found that the slip distance and force variation of intruder is closely tied to the topology of force chain networks in front of the intruder,rather than the evolution of the previous stick event.