Complex Systems Laboratory, Physics Department, Alzahra University, Tehran, P.O. Box 1993891176, Iran
In this paper, we have numerically examined models that are capable of describing free falling regimes of a rigid sphere in a thixotropic fluid as Laponite. By simultaneously solving the dynamical equations governing both sphere and fluid systems, different regimes referred to in the experimental methods, are obtained. Three common behavioral regimes are: i) quickly stopping object, ii) fall with decreasing velocity, and iii) falling with a constant velocity in a steady-state mode. The initial state of the fluids (which is a function of the aging time), the characteristic relaxation time of microstructure's building up under shear, the characteristic thickness of the yielded zone around the sphere, and critical yield stress value besides the diameter and density of the sphere are effective parameters that change the regime.