Analyzing effects of microscopic material parameters on macroscopic mechanical responses in underwater mixing using discrete element method

Abstract

Mixing processes are commonly used to handle powders and grains in several industrial fields, and their performance has been subjected to extensive study. However, research is limited on underwater mixing in novel deep-sea mining applications. Consequently, we adopt a discrete element method (DEM) enhanced by a lubrication model to investigate the underwater mixing process. We focus on the effect of microscopic material parameters on macroscopic mechanical responses in this study. Variations in macroscopic responses are small among DEM samples with a well-controlled initial density; the largest coefficient of variation (cv) is less than 1.4% in normalized forces on the sidewall, and the values of cv are less than 1.0% for other macroscopic responses. A comprehensive parametric study is conducted for elastic moduli and for dissipative parameters. Elastic moduli exhibited a negligible influence, and the effects of dissipative parameters ranged from most significant to most negligible in the order of coefficient of rolling friction, coefficient of friction, coefficient of restitution, and fluid viscosity. We further discuss the network connectivity of force chains and shear-induced size segregation; it was found that an increase in rolling friction increases the connectivity of particles in principal stress chains, which increases the mixing resistance. Size segregation is monitored for DEM samples with particles that initially follow a uniform size distribution: an increase in friction is observed to enhance the segregation and an increase in fluid viscosity to alleviate it. The findings in this paper can advance the understanding of the dynamics of underwater mixing and offer insights for designing mixing systems for granular materials with large variations in material properties.