The Experimental-Simulative Study On The Granular Piling Using The Discrete Element Method

The particulate Discrete Element Method has become a powerful numerical method in analyzing behaviors of granular materials. However, many researchers used to do DEM simulations utilizing different models without experimental validation, only a small number of studies contributed their predicted results in comparison with laboratorial ones with a full set of specified parameters. The ambiguous parameter specification leads to theoretical uncertainty and thus constrains its use in application. Among the various models the model based on classical contact mechanics between two spheres is undoubtedly reasonable, but up to date there has not any experimental evidence to prove.hi this thesis a comprehensive study on the particle piling with sphere elements utilizing the contact-mechanics-based model, mainly for without adhesive dry particles, is presented by means of both numerical and experimental manners in order to give physical evidence for evaluation the feasibility and the applicability of the model. The results in terms of repose angles and visual profiles are compared and analyzed. The particle assembles in simulations are classified as single-layer two-dimensional (SL2D), quasi-two-dimensional (Q2D) and three dimensional for geometrical arrangements, and following approaches are presented:(1) Primary tests were carried out with SL2D simulations, where the parameters affecting the repose angle in piling were analyzed. It shows that, friction between particle surfaces is a main factor affecting the repose angle, and friction between particles and baseboard also affects free piling significantly therefore free rolling along the board needs to be restrained.(2) An easy-to-use method for measuring particle-particle friction and particle-wall friction was developed, with the method the measurement of friction for coarse glass beads and other materials reported with a simple experimental apparatus. Besides, the relationship between the contacting area and the glide friction was analyzed and discussed.(3) A comparative study on piling of coarse glass beads with DEM simulations (both Q2D and 3D) and matching experiments, together with piling experiments of other granular materials were carried out, it shows that the contact-mechanics-based model and the related algorithm are accurate and rational.The main contribution of this thesis can be concluded on two aspects: one is the proposed easy-to-use method for measuring particle friction coefficient and the piling experimental method are quite reliable, though further improvement is needed, the other is the proposed model is firstly proved with reliable evidences so it has a high applicability.