MULTISCALE ANALYSIS OF STOCHASTIC FLUCTUATIONS OF DYNAMIC YIELD OF MAGNETORHEOLOGICAL FLUIDS

The classical visco-plastic models of magnetorheological fluids are essentially phenomenological macroscale descriptions of fluids, incapable of revealing the interaction between suspensions and carrier fluids that results in a stochastic fluctuation of dynamic yield, and incapable of reflecting the impact of external magnetic fields on this fluctuation as well. In the present paper, the dynamical yield behavior of magnetorheological fluids is investigated by upscaling the information of the microscale interaction between particles, employing a large-scale molecular dynamical simulation technique, to the macroscale bulk behavior. We thus conduct a multiscale model of dynamic yield of magnetorheological fluids based on the conservation principle of system energy at different scales, so as to provide seamless information passing. The investigation reveals that the dynamic yield exhibits nonlinear and stochastic fluctuations due to the heterogeneity of sequence and number of cluster-sheet reconstructions with shear fields loading, and the Brownian motion of suspensions with initial random conditions. Besides, we investigate the thermal fluctuation of microscale particle motion, the variation of the relationship between stress and strain, and the variation of the constitutive relationship of shear rate. It is noted that the microscale thermal fluctuation is far more than the macroscale variation since that the upscaling from the microscale to the macroscale results in the degradation of fluctuations. The macroscale variation, meanwhile, is still significant, which is supposed to be considered in the design and optimization of magnetorheological fluids.