J.L. Sproston

Non-linear modelling of an electro-rheological vibration damper

Abstract Mechanical vibration dampers which employ electro-rheological (ER) fluids are capable of providing continuously variable damping forces in response to a suitable electrical stimulus. Such devices are potentially valuable for implementing “optimum” vibration control schemes such as those described by Sevin and Pilkey [1]. However, before serious design studies can begin, more information is required on the kind of forces which are developed by an ER fluid in vibration. This paper describes experiments in which digital processing of experimental records is used to determine viscous and Coulomb friction terms associated with a prototype ER damper. The models are verified through the use of a describing function model which is used to predict the approximate frequency response functions of the vibrating system.

ER fluids in the squeeze-flow mode: an application to vibration isolation

Abstract In this note the authors describe tests which demonstrate the feasibility of employing electrorheological fluids in a novel mode of operation, namely squeeze-flow. Results from a vibration isolation test facility show how control of resonant magnification and high frequency isolation can be achieved by an unusually simple and compact damping device.

A Note on Parameter Estimation in Non-Linear Vibrating Systems

This note describes the application of a non-linear, least-squares parameter estimation algorithm to the problem of determining Coulomb and viscous damping parameters from the harmonic response of a vibrating system.

The influence of pulsed D.C. input signals on electrorheological fluids

Abstract The electrorheological (ER) effect refers to the apparent change in bulk viscosity which can be induced electrically in certain special fluids. There is a growing industrial interest in engineering applications of the ER effect and systems to control torque transmission, fluid flow and mechanical vibrations are currently under development. To facilitate direct interfacing with modern digital controllers it must first be demonstrated that the ER effect can be activated by pulsed signals in place of the usual constant potential. This paper describes experiments on a typical ER device — a clutch for torque transmission — which demonstrate the feasibility of employing pulsed D.C. signals to activate an ER fluid. Moreover it is shown that the use of a pulsed D.C. supply reduces the power consumption of the device and reduces the possibility of an uncontrollable electrical discharge between the electrodes (i.e., the clutch plates).

Preliminary observations on bulk electroconvection in electrically stressed liquid insulants Part I: Experimental investigation

Abstract Electroconvective motions which occur in the bulk of insulating liquids under electric stress are considered. In order to study such motions, an experiment was devised in which a liquid insulant was electrically stressed in rectangular cells of square cross section with different electrode configurations. Using a suitable flow visualisation technique, the resulting motions were found to remain essentially two-dimensional and streakline photographs for the particle paths were obtained. These suggest that electrical shearing forces acting adjacent to the boundaries of the liquid are mainly responsible for the bulk motions in the liquid.

Some observations on bulk electroconvection in electrically stressed liquid dielectrics

Abstract As a means of obtaining the velocity distribution in an electrically-stressed dielectric liquid, namely polydimethylsiloxane, a laser-doppler anemometer using photon correlation techniques was employed. The difficulties involved in choosing the correct seeding particles are discussed and the latex particles finally chosen appear to give an acceptable indication of the liquid movement. These preliminary experiments also provide further evidence of a critical voltage below which no observable movement takes place.

Non-Linear Identification of an Electro-Rheological Vibration Damper

Abstract Mechanical vibration dampers employing electro-rheological (ER) fluids are capable of providing continuously variable damping forces in response to a suitable electrical stimulus. Such devices are potentially valuable for implementing optimum vibration control schemes but, before design studies can begin, more information is required on the dynamics of the damping mechanism. This paper describes experiments in which combined state and parameter estimation is used to determine viscous and Coulomb friction terms associated with a prototype ER vibration damper

The electrorheological effects and its application to torque transmission

The authors present the results of a series of tests aimed at the assessment of ER (electrorheological) fluids in a continuously variable torque transmission device under both DC and AC excitation. Some of the problems which need further study are outlined. In particular, tests conducted on the torque transmission device indicate that the performance is limited by the shear strength of the particular ER fluid used. This shear strength, used here under dynamic conditions, is of course less than that which would be obtained under the more usual (fluid test) static conditions when the strain rate is extremely small. One of the problems being addressed by the authors is concerned not only with the maximum torque capability (since there are numerous industrial applications when 8 nm would be acceptable) but more with the minimum torque transmitted through such a device when the applied field is zero.<<ETX>>

Electro-Convection in Cells with Plane and Wire Electrodes

An experimental and theoretical study has been made of the induced electro-convection of a dielectric oil in glass cells fitted with parallel plane and wire electrodes. From laser doppler anemometer measurements it was found that the steady, well-defined vortex patterns existed in the cells only for a limited period from initial excitation, and that subsequently the motion became less ordered. Flow visualization and streakline photography confirmed that this unsteadiness was due to the bulk movement of the vortices. An explanation of the bulk movement is offered based on the concept of vortex interaction, the theoretical analysis showing good qualitative agreement with experimental observations of a confined vortex pair.