Most of the commercially available magnetorheological (MR) fluids are only tested up to 1200 1/s shear rates but with no magnetic field. Data are rarely available at high shear rates with magnetic field applied. In most of the applications where MR fluids are used, such as MR rotary brakes or MR translational dampers, the shear rates can be in the order of thousands and in some applications, the shear rates could be in the order of ten thousands (1/s) and higher. At these high shear rates, most MR fluids will be shear thinning and Bingham model will be inappropriate to use. The focus of this study is on the mathematical modeling of a drum-type MR rotary brake using the Herschel-Bulkey model.
Little published data exists on the behavior of MR fluids in squeeze mode. Many of the basic properties of MR fluids in squeeze mode are still unknown. In squeeze mode, MR fluids can generate a large range of force associated with a small displacement. As a result, squeeze mode has recently received more attention. This research focuses on modeling and testing MR fluids in squeeze mode. A novel squeeze mode rheometer is designed and built. MR fluid is tested in squeeze mode to evaluate its performance and behavior. The rheometer can test MR fluid under different conditions (gap size, magnetic field density, speed, etc). It utilizes a Gauss meter for direct measurement of the magnetic field density. MR fluid squeeze test results show that MR fluid can deliver a large range of force that is comparable in magnitude to the force in shear mode. The tests also indicate a clumping effect of the fluid when tested in repeated cycles that does not appear to have been documented previously. This paper describes, in detail, the clumping effect and provides possible reasons for this phenomenon. A non-dimensional mathematical model is developed and validated experimentally. The non-dimensional model directly compares the squeeze mode force to the shear mode force. The results indicate that MR fluid in squeeze mode can be used in many applications requiring a large range of controllable force in envelopes that can only accommodate small strokes.
A nonlinear model of monotube hydraulic dampers is presented with an emphasis on the shim stack properties and their effects on the overall damper performance. There has been no published detailed analysis of the effects of shim stack design in a hydraulic damper to date. Other damper models have used simplifying assumptions for the shim stack deflection and effects of the shim stack have not been completely studied. Various parameters affecting the nonlinear characteristics of monotube dampers such as the hysteresis region are studied. The model presented in this paper can be used for design purposes and helps in developing controllable valvings based on shim stacks. It can also be used to design controllable bypasses in hydraulic dampers. The mathematical model is validated by comparison against experimental test results carried out on an OHLINS CCJ 23/8 monotube damper, in CVeSS test facilities.Keywords Shock absorber · Nonlinear damper model · Hydraulic damper design tool · Variational and energy method · Rayleigh-Ritz · Lagrange multipliers A. Farjoud ( ) · M. Ahmadian · M. Craft · W. Burke Center for Vehicle Systems and Safety (
MR fluid squeeze mode investigations at CVeSS have shown that MR fluids show large force capabilities in squeeze mode. It was found that MR fluids in squeeze mode may be used in a wide range of applications such as engine mounts and impact dampers. In these applications, MR fluid is flowing in a dynamic environment due to the transient nature of inputs and system characteristics. The research presented in this article undertakes the problem of dynamic testing and modeling of MR fluid squeeze mounts. Dynamic tests of an MR mount are studied for different applied currents, initial gaps, frequencies, and excitation amplitudes. An effective mathematical model of the MR squeeze mount for steady-state testing was built which includes the effect of the inertia of the fluid. The results show that the compression force and the area of the hysteresis loop increase with the increase of excitation amplitude or applied current and it will decrease with the increase of frequency or initial gap. Also, the inertia effect becomes more significant for higher displacement frequencies. The mathematical model agrees with the test data very well during the compression process and it can be used for the dynamics analysis and the real-time control.
Magneto-rheological (MR) fluids are currently attracting a great deal of attention because of their unique rheological behavior. Many devices have been designed using MR fluids, and of potential interest here are disc-type MR rotary brakes. The plug flow region in MR devices is defined as the region where the fluid is not flowing. The plug flow region plays an important role in design and analysis of MR devices. In MR dampers, the damping coefficient is a function of the plug thickness. In MR valves, the plug thickness is used to control the flow rate through, and the pressure drop across, the MR valve. A MR clutch is performing at the highest efficiency when the entire MR gap is the plug region. For an MR rotary brake, the highest restraining torque is obtained when the entire gap is the plug region as far as there are no wall slip effects. In this paper, using the Bercovier and Engelman constitutive model, the MR fluid flow in disc-type MR brakes is modeled to determine the plug flow region. The resulting system of equations is solved numerically. It is shown that the existence of a plug flow region in the brake will affect the control torque ratio. Better estimation of the plug flow region results in better estimation of the viscous torque.
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