Magneto-rheological damper is one of the most widely used mechanical equipment, which absorbs mechanical shocks by use of magnetic fluid and electrical coil in its structure. In this paper, for the first time, dissipative particle dynamics as a mesoscopic scale modeling method was used to simulate a magneto-rheological damper and its magnetic fluid. Data from 3 categories including magnetic fluids with brand names 122-EG, 132-DJ, and 140-CG have been used and effect of their physical properties on power of damping force have been investigated. Results of modeling show that by increasing shear rate of fluid, shear stress is first increased and, then, it is applied to a constant value, which results in a greater shear stress by applying a stronger magnetic field. It is also observed that, with increasing both maximum piston velocity and strength of magnetic field, maximum power of damping force increased, which in 140-CG is higher than the other fluids. Results of sensitivity analysis show that weight of magnetic particles and strength of dissipative forces have the greatest effect on damping force, in such a way that by increasing weight of magnetic particles and decreasing the dissipative force of particles, accumulation of magnetic particles decrease, so, increasing quality of damping. It was also found that 122-EG is more suitable than other types of magnetic fluids in forming standard magnetic particle chains, and provides a more favorable viscosity distribution for damping.

In this paper, the effects of particles size of Magnetorheological Carbonyl iron powder on damping force and energy dissipation capacity for a Magnetorheological double ended type damper is investigated experimentally. Despite of the considerable researches on the effects of particles size on the viscosity of Magnetorheological fluids, sedimentation of fluids and electromagnetic field intensity in damper, there is no a published work about the effects of iron particles size on the damping force amplitude and energy dissipation capacity of double-ended Magnetorheological damper. Therefore, in the present research, two different Magnetorheological fluids were prepared with the same volumetric percentage of % 35 from two different sizes of Iron particles i.e. 40 µm and 63µm and filled into a double ended type damper. The double-ended damper had three electric coils and was tested in different frequencies, different electric currents and 15 mm displacement stroke. The effects of Magnetorheological fluid particles on produced damping force and energy dissipation capacity were analyzed by extracting force-displacement and force-time curves from experiments. The results showed that the maximum amplitude of damping force is increased with increasing the applied electric current on the damper and the amount of this force for fluid with 63µm particles size is slightly higher than that for the fluid with 40µm particles size. However, the energy dissipation capacity of the investigated damper in all excitation frequencies with the all applied electrical currents for fluid with 63µm particles size was considerably higher than that for fluid with 40µm particles size.