Penetration Depth of Free Falling Intruder into a Particles Bed in Fluid-Immersed Two-Dimension Spherical Particle System

In a system of spherical particles which is entirely immersed in fluid, an intruder is let free fall into the particles bed consisted of 220 particles with height about 13 particles diameter and width about 15 particles diameter, both are in average. The system is placed in a container with height of 40 cm and width of 15 cm. Bed particles have the same diameter of 1 cm, while the intruder has 4 cm. Water is the fluid with density of 1 g/cm 3 and viscosity of 8.90×10 −4 Pa·s, which is assumed to constant during the simulation. Intruder initial height is always the same and bed particles are let to be relaxed for about 2 s from its initial random configuration of 20×11 in height and width of bed particle diameter, before the intruder is dropped into the system. Bed particles has always the same density about 2 g/cm 3 , while intruder density ρ int is varied from 2 to 4.5 g/cm 3 with increment of 0.5 g/cm 3 . It is observed that higher ρ int gives higher penetration depth after the density of 2.5 g/cm 3 . Density of 4.5 g/cm 3 and beyond will give similar final result, since the intruder already reached bottom of the container. An empirical model for penetration depth as function of ρ int is proposed.