  Fluid-particle systems are highly sensitive to particle morphologies. While
many attempts have been made on shape descriptors and coupling schemes, how to
simulate the particle-particle and particle-fluid interactions with a balance
between accuracy and efficiency is still a challenge, especially when
complex-shaped particles are considered. This study presents a Metaball-Imaging
(MI) based Discrete Element Lattice Boltzmann Method (DELBM) for fluid
simulations with irregular shaped particles. The major innovation is the MI
algorithm to capture the real grain shape for DELBM simulations,where the
Metaball function is utilized as the mathematical representation due to its
versatile and efficient expressiveness of complex shapes.The contact detection
is tackled robustly by gradient calculation of the closest point with a
Newton-Raphson based scheme. And the coupling with LBM is accomplished by a
classic sharp-interface scheme. As for refiling, a local refiling algorithm
based on the bounce back rule is implemented. Validations on three settling
experiments of irregular-shaped natural cobblestones indicate the proposed
model to be effective and powerful in probing micromechanics of
irregular-shaped granular media immersed in fluid systems. The potential of
this model on studies of shape-induced physical processes is further
investigated with numerical examples on the "drafting, kissing and tumbling"
phenomenon of pair particles in various shapes.
