DEM Simulation On The Packing Densification Of Cubical Particles Under Vibration

This thesis presents a numerical study of the cubical particle packing under three-dimensional(3D)mechanical vibration by the multi-sphere model and the discrete element method(DEM).The effects of both vibration parameters and material properties on the packing density are comprehensively investigated.The focus is on the analyses of the microscopic properties in terms of coordination number(CN),radial distribution function(RDF),particle orientation,contact networks and force networks.Corresponding mechanisms in the packing densification process are also discussed.Under 3D mechanical vibration,it is found the packing density of cubical particle packing will initially grow to a maximum value and then decrease with the increase of amplitude or frequency.And the highest packing density is achieved when the amplitude is 0.15dv(dv represents the equivalent diameter of the cubical particle)and the frequency is 100Rad/s.For the effects of material properties of particles on the packing density,the results indicate the sliding friction coefficient has a strong effect on the packing density,while the effects of rolling friction coefficient,restitution coefficient and the shear modulus are less significant.But the shear modulus to some extent can affect the choosing of vibration parameters.The packings of two other rectangular cuboid particles(the ratios of length versus width versus height are 1:1:2 for the Number 1 cuboid and 3:5:9 for the Number 2 cuboid)are simulated and compared together with the cubical particle packing.It is shown the cubical particle packing can achieve the highest packing density,the Number 1 cuboid can get the second highest packing density,while the lowest packing density is obtained in the packing of the Number 2 cuboid particles.The packing structures at different densification stages are analyzed in a microscopic view.The peak of CN distribution shifts to right when vibration conditions are initially carried out,while it almost keeps stable under the value of 6 even with the further implementation of the vibration,which is actually associated with the geometrical characteristics of cubical particles.The variation of the peaks in RDF distributions shows the coherence of cubical particles will gradually increase in the densification process with the emergence of short-range order phenomena,which will even tend to become long-range order with the further densification degree.The analyses of radial packing density,particle orientation,contact networks and force networks all indicate that in the densification process the ordered structures will firstly form near the walls of the container,and then expand into the inner parts of the packing system.Such observations prove the container walls are critical for the formation of the packing structure of cubical particles.Based on the microscopic analyses of the densification mechanisms,it is demonstrated that the transition of the cubical particle packing by total feeding from the initial random state to the ordered state can be realized with the proper choosing of the container shape and 3D vibration parameters.