Electrorheological fluid controllable journal bearings

Experimental measurements of electrorheological fluids on Couette type viscometers revealed the one dimensional shear stress constitutive relation at shear strain rates up to 20000 ;A theoretical investigation of the balance laws of the electro- hydro- and thermo-dynamics was undertaken to identify appropriate state variables characterizing electrorheological fluids and obtain the conditions for thermodynamic admissibility of constitutive relations. A generalized Bingham fluid model with parameters depending on the electric field strength was adopted as thermodynamically admissible and further, an adequate approximation only for journal bearing lubrication flows. This constitutive model is an approximate extension of the experimental one dimensional shearing relation and it is not believed to predict more general flows of electrorheological fluids because it includes a yield stress independent of the electric field direction.;The lubrication approximation of the above balance laws leads to a generalized non-linear Reynolds' equation based on the above Bingham type model. Moreover, it is predicted that some regions of the electrorheological fluid remain unyielded while other regions flow. This highly non-linear Reynolds' equation for the pressure was solved by iterative numerical techniques. Results indicated an increased load capacity of the journal bearing with the increase of the electric field.;To validate both modeling of the ER-fluid and the numerical simulations, a prototype pad journal bearing was built. The numerically predicted pressure distribution is in close agreement with the experimental one. Further numerical predictions of the effect of the electric field on the equilibrium position and the dynamic characteristics of the bearing are produced.