Physical And Numerical Study On The Vibrated Packing Densification Of Conical Particles

Based on the limited studies on the packing of non-spherical particles,various conical particles with different aspect ratios(e.g.the ratio of height and bottom diameter of a conical particle)were selected as the research target and their packing densification under 3D mechanical vibrations were both experimentally and numerically(using DEM simulations)carried out in current work.And various macro and micro properties of the packing structures were characterized.Following aspects are highlighted:(1)The influences of operation parameters including vibration amplitude,vibration frequency,container size and so forth on the packing densification process of conical particles with different aspect ratios are systematically investigated.And corresponding maximum packing densities as well as optimal vibration parameters are obtained.(2)The obtained packing structures of conical particles are reconstructed using the well-known CT non-destructive inspection technique.In addition,the macro properties(packing density and porosity)and the micro properties(coordination number,radial distribution function,particle orientation function)are carefully characterized and analyzed.(3)The dense packing structures of conical particles obtained from numerical simulations are characterized in both macro-and microscopic levels.Corresponding results are compared with those obtained from experiments.The contact types of the conical particles with different aspect ratios are also carefully and statistically classified.Corresponding densification mechanism is also further explored.Based on the results and analyses,we find that:1)The influences of vibration conditions on the macro properties of conical particle packing in numerical simulation are quite agreeable with those in experiments.The packing density of each type of conical particles increases with the augment of vibration amplitude A and vibration frequency ? to a high value and then decreases.And the variation of packing density is more sensitive to vibration amplitude than to vibration frequency.The highest packing density ?=0.7162 is obtained from the conical particles with aspect ratio of 0.866 under the optimal vibration conditions of A=0.5 mm ?=160 Rad/s.2)The analyses of the porosity distributions for the dense packings of conical particles obtained from physical experiments reveal that no obvious stratification can be observed.RDF analysis shows that the bottom-bottom contact of conical particles decreases with the increase of aspect ratio.And the bottom-side contacts are always existed within the packing,yet the contact type which can be indicated from the peak value of RDF changes as the particle shape varies.3)The variation of contact type within packing structures are also carefully analyzed from numerical simulations.The results show that a much denser packing bed can be formed when the contact type contributing to more regular local packing structures increases or that leading to large voids of packing structure decreases.4)The analysis of nematic order parameter implies that the packing structures of all types of conical particles are random.And the randomness rises with the augment of aspect ratio.