No abstract

Magnetorheological fluids involve multi-physics phenomena which are manifested by interactions between structural mechanics, electromagnetism and rheological fluid flow. In comparison with analytical models, numerical models employed for magnetorheological fluid applications are thought to be more advantageous, as they can predict more phenomena, more parameters of design, and involve fewer model assumptions. On that basis, the state-of-the-art numerical methods that investigate the multi-physics behaviour of magnetorheological fluids in different applications are reviewed in this article. Theories, characteristics, limitations and considerations employed in numerical models are discussed. Modelling of magnetic field has been found to be rather an uncomplicated affair in comparison to modelling of fluid flow field which is rather complicated. This is because, the former involves essentially one phenomenon/mechanism, whereas the latter involves a plethora of phenomena/mechanisms such as laminar versus turbulent rheological flow, incompressible versus compressible flow, and single- versus two-phase flow. Moreover, some models are shown to be still incapable of predicting the rheological nonlinear behaviour of magnetorheological fluids although they can predict the dynamic characteristics of the system.

A novel design of a magnetorheological (MR) damper is developed, fabricated, modelled and tested. The design includes some features that enhance the magnetic characteristics of the damper. The iron-cobalt-vanadium "Vacoflux-50" alloy and the "AMT-Smartec + " MR fluid, whose magnetic characteristics have been predicted to enhance the performance of the damper, are employed in the new design. Moreover, the location of the MR fluid region in the piston construction has been chosen so that the magnetic field maximises. To evaluate the impact of the proposed design improvements, an approach to modelling the performance of a previously-tested MR damper of a different design, different magnetic material, and different MR fluid has been developed. The approach combines a Finite Element Analysis (FEA) of the magnetic circuit, and a nonlinear analytical model of fluid flow. The results of the FE/analytical approach have been validated using the available published results of the same damper. Hence, the approach has been used to predict the performance of the same damper due to the employment of the proposed design improvements. The FE/analytical approach accounts for the nonlinear characteristics caused by the magnetic saturation of materials and the effects of fluid compressibility and aeration in the damper. It has been found that the implementation of the proposed design features leads to a remarkable increase in the magnetic field and the fluid yield stress. Also, the inclusion of the nonlinear magnetic and fluid flow characteristics have been found to affect the magnetic field distribution and the fluid yield stress greatly.