Normal Instantaneous Squeeze Film Force for a Finite Length Cylinder

A theoretical model for the normal instantaneous squeeze film force for a finite length cylinder is developed in this paper. The model assumes large unidirectional cylinder motion along a sleeve diameter. Based on the assumption of a parabolic flow field, a normal squeeze film model for an infinitely long cylinder is first obtained. Combining the infinitely long model with side-leakage factors, a finite length model is then obtained. The model shows that the instantaneous squeeze film force consists of three position-dependent nonlinear terms: namely a viscous term, an unsteady inertia term and a convective inertia term. From experimental measurements using water and a clearance to radius ratio of 0.032, the viscous term of the theoretical model should be corrected by a factor involving the instantaneous squeeze film Reynolds number and the absolute value of instantaneous eccentricity. The synthesized squeeze force waveforms obtained using the corrected equation with averaged weighting coefficients agree very well with the experimental waveforms for eccentricity ratios up to 0.9 and a wide frequency range. The corrected equation is suitable for the calculation of the normal instantaneous squeeze film force given the instantaneous position, velocity, and acceleration of the cylinder center.