| Abstract [eng] |
In the dissertation analysis of literature and patent material in aspects of research, monitoring and maintenance of the magnetorheological fluids was performed. Familiarized with several methods for monitoring sedimentation in MR fluids, and several devices for mixing these fluids and their disadvantages were identified. Also particle movement in the MR fluid was mathematically described when they are in the middle of the tube or near the wall. It has been found that when the particle is closer to the tube wall, so its speed is lower due to friction forces. A mathematical model is described where an infinite strip is affected by harmonic oscillations. The stationary and dynamic components of tangential force are described. Combining two theories - resistance to the magnetic field and determination of the degree of sedimentation, the formula of the degree of resistance to sedimentation is derived. The theoretical and experimental results were compared. Their character is very similar, and the correlation coefficients for all five researched fluids are more than 0.95. Five different fluids were tested by rheometer. Shear stress dependences of each fluid on the shear rate with and without the action of the magnetic field were obtained. Three special sensors to determine electrical resistivity in the MR fluid were created. This method was verified experimentally and compared to another inductance of the coil measuring method. As this method was compared with other methods worldwide, main advantages of this method are easy to adapt, it is cheaper and simpler than other similar devices. The experiment of the determination of torque moment of MR brake was carried out. Because the sedimentation of the magnetorheological fluid affects the working efficiency of MR brake, the device to determine sedimentation level was placed inside the brake. The sedimentation level of MR fluid inside tested MR brake was determined by microcontroller measuring the electric resistivity of top and bottom sensors. When the level of sedimentation reaches its limit piezo actuators turn on and mix MR fluid inside the brake. |
