Dynamic normal force of MRF in non-uniform fields: a COMSOL simulation study

Abstract Currently, most studies primarily focus on analyzing the static normal force of magnetorheological fluids under uniform magnetic fields. However, in non-uniform magnetic fields, MR fluids generate normal forces with varying directions and magnitudes. The uncontrollability of these dynamic forces under real-world conditions leads to engineering challenges, such as increased vibration in MR devices and sealing failures. Although some scholars have investigated the static normal force of MR fluids in non-uniform fields, there remains a lack of accurate mathematical models describing how dynamic normal forces are generated by external shear in such fields. To address this gap, this study provides a mathematical framework for the dynamic normal force of the MRF in non-uniform fields. Firstly, this paper derived a theoretical model for the dynamic normal force of MR fluids under shear in non-uniform magnetic fields, a finite-element model of the MCR-302 flat-plate rheometer and a material model of the MR fluid were then developed using COMSOL. Additionally, fluid-solid coupling simulations between the MR fluid and the test rotor in the MCR-302 rheometer were implemented in COMSOL to analyze interactions under non-uniform fields, Subsequently, the dynamic normal force was calculated in conjunction with the theoretical model and experimentally verified using a flat-plate rheometer. Finally, a comparison of simulation and experimental data showed consistent results, confirming the accuracy of the theoretical model and demonstrating the feasibility of the COMSOL fluid-solid coupling method.