Superparamagnetic micro-bead chains and microswimmers under the influence of an oscillating magnetic field are studied experimentally and numerically. The numerical scheme composed of the lattice Boltzmann method, immersed boundary method, and discrete particle method based on the simplified Stokesian dynamics is applied to thoroughly understand the interaction between the micro-bead chain (or swimmer), the oscillating magnetic field, and the hydrodynamics drag. The systematic experiments and simulations demonstrated the behaviors of the microchains and microswimmers as well as the propulsive efficiencies of the swimmers. The effects of key parameters, such as field strengths, frequency, and the lengths of swimmer, are thoroughly analyzed. The numerical results are compared with the experiments and show good qualitative agreements. Our results proposed an efficient method to predict the motions of the reversible magnetic microdevices which may have extremely valuable applications in biotechnology.

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� �Yasushi IDO (Mem.), Kazuya ARAKAWA, Hirotaka SUMIYOSHIBehavior of micrometer-size magnetic particles in a simple shear flow of magnetorheological fluids is investigated by using numerical simulation. Hybrid simulation method which combined both HSMAC method and discrete particle method based on the simplified Stokes dynamics is performed. Behaviors of magnetic particles in shear flows between two parallel plates are simulated. Chain-like clusters appear and they are combined each other to form wall structure in the presence of magnetic field in the static state. In the weak shear flow, such clusters move with flow, however, magnetic particles are rearranged as layered sheet-like structure in the rather strong shear flow.