“…Since two decades ago, researchers have done lots of work on dynamics of particles' freefalling in fluids both experimentally and numerically (Ardekani, Dabiri, & Rangel, 2008;Feng & Michaelides, 2004;Goyal & Derksen, 2012;Hu, 1996;Huang, Hu, & Joseph, 1998;Pu, Shao, Huang, & Hussain, 2013). Among the numerical methods, finite element method (FEM) (Jotsa & Pennati, 2015;Liu & Quek, 2013), finite difference method (FDM), finite volume method (FVM), and even meshfree methods (Liu, 2009;Pu et al, 2013) are most widely used. Hu, Joseph, and Crochet (1992) used FEM to model the Navier-Stokes equations for liquid and the Newton's equations of motion for solids.…”