resistance force on a spherical intruder in fluidized bed

Insertion of large objects or intruders into granular material is common both in nature and industrial applications. during penetration due to collision between intruder and granular particles, intruder experiences resistance or drag force (analogy from fluid). in literature, it is extensively studied that in dry packed beds granular drag force increases with the intrusion depth. however, nearly no information is available about the effect of fluidization on the granular drag force and is the main theme of this paper. in this paper, discrete element method (dem) and computational fluid dynamics (cfd) is used for performing numerical simulations. simulations showed that granular drag force becomes independent of intrusion depth at incipient fluidization and is a function of reynolds number. using the mathematical relation of fluid drag force, granular viscosity of the fluidized bed is calculated. the physics for the fluid like state of granular material and the independence of granular drag force with intrusion depth is explained at the end of paper.