W. A. Bullough

Controllable viscous damping: an experimental study of an electrorheological long-stroke damper under proportional feedback control

It is now well known that smart fluids (electrorheological (ER) and magnetorheological) can form the basis of controllable vibration damping devices. With both types of fluid, however, the force/velocity characteristic of the resulting damper is significantly nonlinear, possessing the general form associated with a Bingham plastic. In a previous paper the authors suggested that by using a linear feedback control strategy it should be possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors describe a comprehensive investigation into the implementation of this linearization strategy on an industrial scale ER long-stroke vibration damper. Using mechanical excitation frequencies up to 5 Hz it is shown that linear behaviour can be obtained between well defined limits and that the slope of the linearized force/velocity characteristic can be specified through the choice of a controller gain term.

Trends in acoustic properties of iron particle seeded auxetic polyurethane foam

Abstract The sound absorption characteristic of a clean, open-cell configuration, typical polyurethane flexible foam is shown against that of an auxetic foam made from it, and this same foam after it has been seeded with a magnetorheological fluid (then dried), having 2–5 μm carbonyl iron particles and subjected to zero, weak and concentrated magnetic fields in an acoustic impedance tube facility. The resultant foam indicates the capability of shifting the peak acoustic absorption coefficient within a given frequency bandwidth when constant intensity magnetic fields are applied.

Dynamic modelling of an ER vibration damper for vehicle suspension applications

In this paper, the authors describe the development of a mathematical model of a controllable vibration damper intended for eventual application to ground-vehicle suspension systems. The damper under investigation employs electro-rheological (ER) fluid as the working medium which enables a continuously variable damping force to be provided in response to an electrical control signal. There are some difficulties inherent in characterizing the ER dampers behaviour which the present study attempts to overcome. The paper begins by describing a novel form of non-dimensionalization which drastically reduces the number of variables required to characterize the quasi-steady behaviour of the ER fluid. The construction of the ER damper is described and, on the basis of physical reasoning, it is shown how a dynamic model can be derived by taking account of ER fluid inertia and compressibility. A recently developed iterative scheme is introduced in order to solve the resulting non-linear equations of motion. The paper concludes with a case study involving the application of the ER damper to controlling the lateral vibrations of a rail vehicle.

On the phenomenological modeling of electrorheological and magnetorheological fluid preyield behavior

Phenomenological constitutive models for electrorheological and magneto-rheological fluids and devices in the literature have used various approaches for the representation of the preyield regime. These include modeling the preyield regime using an elastic spring, a viscous dashpot, a Kelvin–Voigt solid, a Maxwell fluid, a three-element (Zener) solid, and a three-element fluid. This paper reviews the behavioral attributes associated with each of the above models. Then, considering the physical phenomena prior to the onset of yield, and experimental data in the preyield regime, and comparing with the behavioral attributes exhibited by the various preyield models, it is concluded that the behavior in the preyield regime is solid-like, not fluid-like, and most conveniently represented as a Kelvin–Voigt viscoelastic solid. In particular, over frequency ranges of interest, the storage modulus does not approach zero at low-frequency limits, as a fluid would exhibit. Effectively modeling the preyield behavior as a Maxwell fluid, as has been done in the literature, yielded frequency-dependent system parameters (specifically the preyield viscosity). This is the result of a viscoelastic fluid model attempting to display the viscoelastic solid-like characteristics exhibited by the test data.

Decomposition of the Pressure Response in an ER Valve Control System

Experimental data from tests on an ER valve pertinent to the development of a con troller for high speed machine duty has been analysed to show that three common, underlying modes of response are present. This is demonstrated for a range of industrial scale flow velocities and electrode dimensions, in the time and frequency domains. The dependence of steady-state pressure on the electric field is also discussed.

Smart Fluid Damping: Shaping the Force/Velocity Response through Feedback Control

It is now well known that smart fluids [electrorheological (ER) and magnetorheological (MR)] can form the basis of controllable vibration damping devices. With both types of fluid, however, the force/velocity characteristic of the resulting damper is significantly non-linear, possessing the general form associated with a Bingham plastic. In a previous paper the authors showed that by using a linear feedback control strategy it is possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors illustrate an extension of the technique, by showing how the shape of the force/velocity characteristic can be controlled through feedback control. This is achieved by using a polynomial function to generate a set point based upon the damper velocity. The response is investigated for polynomial functions of zero, 1st and 2nd order. It is shown how the damper can accurately track higher order polynomial shaping functions, while the zero-order function is particularly useful in illustrating the dynamics of the closed-loop system.

A proportionate coulomb and viscously damped isolation system

Abstract The results of a computer study aimed at assessing the usefulness of a controllable, variable effect, non-linear damper in a vibration isolation system are given. This is done by showing the effect on the performance of a simple model suspension system of the addition of a controllable spring/damper link. The damping characteristic of the controllable element is that of a viscous damper with a threshold force required to move it; the viscous rate is fixed whilst the threshold force is pre-selected. This is an idealized form of the characteristic to be expected from a prototype damper which operates on electroviscous fluid and is controlled by imposing an electric field on the associated electroviscous valve or shear plate. The results indicate that a significant degree of control may be expected for a wide range of sprung mass.

The Electro-Rheological Clutch: Design, Performance Characteristics and Operation

Fluid power transmission based on the electro-rheological clutch is taken beyond the concept-proving stage. A typical electro-rheological fluid is characterized over a range of engineering conditions and is found to usefully approximate to a continuum of Bingham plastic form. The clutch is optimized from this standpoint, and the limits of its performance are estimated. The state of the art is discussed alongside an outline of the infrastructure required to achieve maximum potential.

Feasibility Study on the Storage of Magnetorheological Fluid Using Metal Foams

This article presents an original idea: the use of metal foams to store unexcited magnetorheological fluid (MRF) in such a way such that the fluid mixture can be propelled when excited. This work is motivated by the desire to overcome the need for costly dynamic seals for conventional MRF dampers. The results of metal foam characteristics, possible changes in the content of propelled MRF, and the responses of soaked MRF when excited are presented. A plate-on-plate test rig was developed to investigate the performance of the MRF-soaked metal foam set-up. The shearing performance, response time, gap effects and the influence of different metal foams were investigated experimentally. The results show that the MRF can be magnetically propelled into the gap between the plate and the metal foam surface, and shearing resistance is produced on the rotary plate. Shearing performance is sensitive to the volume of the propelled MRF, gap clearance, and the strength of the external magnetic field. The response of the proposed MRF-soaked metal foam set-up is slower than that of the conventional MRF-filled two-plate configuration simply because it takes time to propel the MRF. This primary investigation shows that MRF-soaked metal foams can produce MR effects.

Dynamic simulation and performance of an electro-rheological clutch based reciprocating mechanism

A reciprocating mechanism which utilizes two electro-rheological clutches is described. An industrial application of the mechanism is in winding filaments onto bobbins. The required traverse speed is 5 m s-1 with a turn-round period of 10-20 ms, the traverse length is 250 mm and the turn-round position must be electronically controllable and repeatable within the ±1 mm. These combined criteria of high-speed and controllability makes the use of electro-rheological fluids an attractive proposition. The operation of the reciprocating mechanism and the dynamic model used to simulate the performance are outlined. The simulation is verified by comparison with experimental results from a prototype mechanism. Simulations are made to illustrate the effect of various fundamental electro-rheological fluid characteristics, such as electro-shear stress, time delays and viscosity. These simulations are considered in relation to the requirements for the operation of the high-speed mechanism.