Simulations of particle dynamics in magnetorheological fluids

We present particle dynamics simulations for the response of magnetorheolog ical (MR) fluids upon application of a magnetic field. The particles motion is considered to be governed by magnetic, hydrodynamic, and repulsive inte ractions. Fluid-particle interactions are accounted for via Stokes' drag wh ile inter-particle repulsions are modeled through approximate hard-sphere r ejections. In accordance with their greater significance, on the other hand (linear) magnetic interactions are fully simulated. The time evolution is considered to be magnetically quasi-static and magnetostatic forces are der ived from the solution of (steady) Maxwell's equations. recomputed at each instant in time. For this we use a potential theoretic formulation where th e boundary integral equations are solved with a fast multipole approach. We show that the resulting numerical codes can be effectively used to study a number of experimental observables such as effective magnetic permeabiliti es and response time-scales which are of crucial importance in the design o f MR fluids. (C) 1999 Academic Press.