The magnetorheological fluids are classified as smart materials with controllable rheological properties. The fast growing application of magnetorheological fluids in recent years has increased the...

A review on the simulation and modeling of magnetorheological fluids

In magnetorheological (MR) fluid, the rheological properties can be changed in a controlled way, the changes being reversible and dependent on the strength of the magnetic field. The fluids have potentially beneficial applications when placed in various geometrical arrangements. The squeeze mode is a geometrical arrangement where two flat parallel solid surfaces, facing each other, are pushed towards each other by an external force operating at right angles to the surfaces. The liquid initially in the gap between them is free to move away from this increasingly small gap, and it does so by flowing parallel to the surfaces, and collecting in a region where it is no longer in the gap between them. The performance of an MR fluid in compression (squeeze) mode has been studied with the magnetic field being generated by a coil carrying different magnitudes of DC electrical current. A test rig was designed to perform this operation with the flat surfaces being horizontal and being pushed together in a vertical direction and the liquid being forced to move in all directions in a horizontal plane. The rig operated by decreasing the size of the gap at a constant rate. For each trial the current in the coil was kept constant and the instantaneous compressive force was recorded. When plotting compressive stress against compressive strain for each trial, the slope of the curve was found to be larger in general when the current was larger. This was an expected result; however, the behaviour is more complicated than this. For a significant range of values of compressive strain, the slope falls to zero, so that the compressive stress shows no increase during this period while the compressive strain continues to increase. The details of this behaviour are strongly dependent on the initial size of the gap.

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The performance of magnetorheological fluid in squeeze mode

Conventional squeeze film dampers (SFDs) have shown their effectiveness in suppressing unbalanced vibrations in rotor systems, particularly supported by rolling element bearings. Recently, there is an increasing demand for 'controllable' SFDs to meet the need of modern rotating machinery, characterized by high operating speed and high load capacity. Thus, this paper presents a controllable semi-active SFD using magneto-rheological (MR) fluids, focusing on its design and modeling. It offers a comprehensive design method and an innovative experimental identification and modeling technique for MR-SFDs. The primary goal of the MR-SFD design is set to maximize its dynamic control bandwidth, and the design method includes the material selection, magnetic circuit analysis and sealing element design. After constructing a prototype MR-SFD based on the final design, this work investigated how some of the critical design parameters affect the performance of the MR-SFD (i.e. its dynamic control bandwidth change). Furthermore, it characterized the damper's dynamic behavior experimentally using a novel excitation method that adopts active magnetic bearing (AMB) units. Unlike conventional methods, the AMB system was able to precisely control the amplitude and frequency of the input excitation, enabling us to obtain the nonlinear dynamic stiffness properties of the MR-SFD with varying input current. In modeling the dynamic behavior of the MR-SFD, this study employed the describing function method. The describing function analysis effectively captured the nonlinear dynamic behavior of the MR-SFD.

https://iopscience.iop.org/article/10.1088/0964-1726/17/3/035006/pdf

Design and modeling of semi-active squeeze film dampers using magneto-rheological fluids

Following recent rapid development of researches in utilizing Magnetorheological (MR) fluid, a smart material that can be magnetically controlled to change its apparent viscosity instantaneously, a lot of applications have been established to exploit the benefits and advantages of using the MR fluid. One of the most important applications for MR fluid in devices is the MR valve, where it uses the popular flow or valve mode among the available working modes for MR fluid. As such, MR valve is widely applied in a lot of hydraulic actuation and vibration reduction devices, among them are dampers, actuators and shock absorbers. This paper presents a review on MR valve, discusses on several design configurations and the mathematical modeling for the MR valve. Therefore, this review paper classifies the MR valve based on the coil configuration and geometrical arrangement of the valve, and focusing on four different mathematical models for MR valve: Bingham plastic, Herschel–Bulkley, bi-viscous and Herschel–Bulkley with pre-yield viscosity (HBPV) models for calculating yield stress and pressure drop in the MR valve. Design challenges and opportunities for application of MR fluid and MR valve are also highlighted in this review. Hopefully, this review paper can provide basic knowledge on design and modeling of MR valve, complementing other reviews on MR fluid, its applications and technologies.

A review of design and modeling of magnetorheological valve

Magnetic circuit design for the squeeze mode experiments on magnetorheological fluids

By using magnetorheological (MR) fluid in place of lubricating oil in a traditional squeeze film damper (SFD), one can build a variable-damping SFD, thereby controlling the vibration of a rotor by controlling the magnetic field. Assuming a Bingham model, the Reynolds equation for an MR fluid squeeze film is developed and solved to provide expressions for the velocity, the pressure distribution and the damping force. Electromagnetic theory is used to calculate the magnetic pull force between the magnetic poles in the damper. The mechanical properties of the squeeze film and the unbalance response characteristics of an MR fluid SFD–rigid rotor system are analyzed theoretically. An MR fluid SFD is designed and manufactured, and the unbalance response properties and control method of a flexible rotor supported on the damper are studied experimentally. The study shows that the magnetic pull force can decrease both the first critical speed and the critical amplitude; the film damping force can decrease the amplitude at the undamped critical speeds, but increase the amplitude in a speed range between two undamped critical speeds. The damper may have the best control effect to minimize the vibration within the range of all working speed by using the on–off control method.

https://iopscience.iop.org/article/10.1088/0964-1726/14/4/011/pdf

Dynamic performance and control of squeeze mode MR fluid damper–rotor system

Using magnetorheological (MR) fluid in place of lubricating oil in a traditional squeeze film damper (SFD) can build a variable-damping SFD controlled by an magnetic field, and can be used to control the vibration of rotor systems. The structure of an MR fluid SFD is introduced. The Reynolds equation of the MR fluid squeeze film is derived and solved based on the Bingham model, and the formulas for flowing velocity, pressure distribution, film force, and the magnetic pull force of the damper are presented. The mechanical properties of the squeeze film and the unbalance response characteristics of the MR fluid damper-rigid rotor system are analyzed theoretically.

N. Feng

Papers

Dynamic performance and control of squeeze mode MR fluid damper–rotor system

Vibration control of rotor by squeeze film damper with magnetorheological fluid

Vibration control of rotor by squeeze film damper with magnetorheological fluid