Identification of Non-Linear Force Coefficients for the Radial Motion of a Squeeze Film Damper

Abstract

The fluid force generated in a squeeze film damper undergoing large amplitude radial motion is described in terms of non-linear hydrodynamic inertial and damping coefficients, together with afluid static force. Linear-in-the-parameter polynomial forms are introduced to represent the variation of these contributions with radial position. A generalized state variable filter identification method is developed which enables all the parameters in the non-linear model to be estimated from experimental data. The method is validated by processing simulated data and then applied to some new experimental data. Experimental results, relating to the influence of the supply pressure and the operating frequency on the coefficients, are presented and discussed. Comparisons are made with corresponding predictions derived from existing lubrication theory. The parametric non-linear model is found to give a good fit to experimental data over a significant region within the vicinity of the initial static equilibrium position. Through a combination of results, the variation of the fluid force coefficients and the fluid static force with eccentricity, over nearly the whole range of the radial clearance, is obtained. Temporal inertia is found to be more important than convective inertia for motion near the centre of the clearance circle. The existence of a fluid static force, suggested by previous work is confirmed. It is found that this force is linearly proportional to the oil supply pressure.