Study On The Theory Of DEM With An Interstitial Fluid

The Discrete Element Method (DEM) is a powerful tool in analyzing granular assembly. The granular discrete element method can be applied to the partials, whose shape can be approximately described as a sphere. The research of the squeeze flow between two disks is the basic study on the squeeze flow between two spheres. Due to the interstitial fluid between the partials, the solutions of the pressure and tangential force between the two granules are the theoretical foundation of the wet granular discrete element method. Therefore, it is important to study the forces between two granules with interstitial fluid.1. Squeeze flow between two parallel disks is considered for small gaps for rigid-plastic material with partial wall slip. Firstly, the Coulombic friction condition is discussed, and a new pressure distribution is obtained. Moreover, based on the assumption that the slip velocity at the disks increases linearly with the radius up to the rim slip velocity, another pressure distribution is derived by introducing a appropriate velocity field. Then these different results by the different friction conditions and technique are compared.2. Based on the Reynolds' lubrication approximation, the small parameter method is introduced to approximately analyze velocity field and stress distribution between the two parallel disks with an interstitial second-order fluid.3. Squeeze flow between two parallel plates of a Bingham fluid with partial wall slip is considered. The results show that the squeeze viscous force decreases with the slip parameter increases, rigid region of the fluid increases with the slip parameter increases. When the slip parameter tends to infinite, the results of the squeeze viscous force reduce to the case of the squeeze flow of rigid-plastic solid between two parallel disks.4. Based on the Reynolds' lubrication approximation, and utilizing the small parameter method, the velocity and the pressure equations for two spheres translating normally and tangentially with an interstitial second-order fluid are derived for modeling wet granular assembles using the Discrete Element Method. As a result, analytical solution for the tangential force and the torque were obtained. It is interesting to find that, although the equations for the velocity and the pressure are more complicated in their form than a Newtonian fluid, however, the final results are simple and the same as those for a Newtonian fluid.5. When two spheres with an interstitial Herschel-Bulkley fluid translate normally, the velocity and the squeeze force distributions are investigated. It is shown that the solution of the squeeze force can reduced to the Bingham and power-law fluid cases, respectively.6. Applied the above theory and the DEM program TRUBAL, the unilateral compress problems for the regular generated particles with an interstitial fluid are studied, and the macro-strain-stress curves varied with the fluid properties and the velocity of the wall are gotten. Then, he unilateral compress problems for the random generated particles are numerically simulated, and the macro-strain-stress curves are obtained. Moreover, the numerical simulation results for the dry and moist cases are compared.7. Finally, the application of the discrete element method with an interstitial fluid is discussed. For this purpose, a dynamic compacting process and a retaining wall problem are simulated by DEM. It is shown that these problems can be qualitatively analyzed by DEM.The present results of the interaction between two particles with an interstitial fluid provide a new sight and model for DEM, and show a potential usage in application.