ANALYTICAL MODELING OF MR FLUID DAMPERS

Abstract

Semi-active control systems are becoming more popular. because they can offer the combined, advantages of both, passive and active control systems, viz., reliability of passive systems and versatility of active control systems without imposing heavy power demands. Magneto-rheological (MR) fluids can be used to design very effective vibration control actuators named as MR dampers. The MR damper is a control device that consists of a hydraulic cylinder filled with magnetically polarizable particles suspended in a carrier fluid. A MATLAB-Simulink model of a 20-ton MR damper is prepared and the effect of input current, displacement amplitude, and frequency of harmonic excitation on the mechanical properties of MR damper, such as damping force, equivalent damping capability, are studied. A simpler analytical model for MR dampers is proposed. The functional dependence of maximum force developed by MR damper and its• - equivalent viscous damping coefficient, on input parameters to the damper is presented in this work. It is found that the performance of the simpler analytical model proposed in this study, is well in accord with actual MR damper performance. Using the Matlab-Simulink, the MR damper is incorporated in a single degree of freedom (SDOF) system and its effectiveness in vibration suppression of SDOF system under various base excitations is presented in detail_ The study of effects of MR damper placement on the vibration parameters of a 3-storey shear building is also included in this dissertation work. It is found that the position of MR damper in building affects the equivalent damping ratio of the building significantly. The best position to place the MR.damper in a building is found to be the first floor of the building and in this case MR damper adds maximum additional -damping to the building. The variation of additional damping to building with respect to input current to damper is also studied and it is found that after a certain value of input current there is no appreciable change in additional damping ratio to building with increase in input current. Based on this study a sensitive current range for MR dampers is also suggested.