DEM Dynamical Simulation Of Regular Octahedral Particle Packing Densification And Structure Characterization

Multi-sphere discrete element method is used in this thesis to simulate the three dimensional vibrated packing densification of regular octahedral particles.Corresponding physical experiments are carried out to validate the proposed numerical simulations.The effects of vibration parameters on the densification process are studied.The characterization on macro property and various micro properties of different packing structures is presented based on the numerical simulations.In the physical experiments and the numerical simulations on macro packing property of vibration densification,initial loose natural packing is formed by feeding particles into the cylindrical container with a certain rate and then the dense final packing is realized by applying vibration to the container.It is found that the densification process is relatively sensitive to the change of vibration amplitude and is insensitive to the vibration frequency under most vibration amplitudes.The vibration amplitude suitable for obtaining the densest packing is in a relatively wide range.The vibration frequency is also in a wide range coupled with the corresponding vibration amplitude.The physical experimental validation demonstrates the effectiveness of the numerical simulation.In both initial natural loose packing and final vibrated dense packing,there are three obvious packing layers of particles near the side wall and the bottom of the container.Eliminating the wall effects,the central areas maintain constant packing densities,i.e.0.670 for initial loose packing and 0.684 for final dense packing.The neighboring particles in the packing are most probably arranged with the distance between the particle centers almost possessing the minimum value while the real face-face contacts with the two contacted faces in coincidence are relatively rare.In the whole packing structure,the coordination number and number of constraints both decrease during vibrated packing densification and those at the boundary are always lower than those in central area.The densification process accompanies with the decrease of the contacts with high constraint(face-face contacts and face-edge contacts).Onlythe first layer of particles which are next to the container wall indicate some ordered arrangements.The particles in the inner part of the packing always maintain a good orientational randomness.So it can be concluded that the structures corresponding to the two packing densities for the initial loose packing and vibrated final dense packing have a good randomness in the aspects of particle position and orientation.The analysis indicates that regular octahedral particle packing densification has its own regulations and characteristics for various micro properties.These micro properties are obviously different from the ones of particles with other shapes such as spheres and cubes.So specific packing properties cannot be predicted according to the particle shape.