Linear Force Coefficients Research Articles

Estimation of Linearized Force Coefficients for Cylindrical Squeeze Films

Linearized damping and inertial coefficients for cylindrical squeeze films with centered and off-centered elliptical motions have been determined, experimentally through a generalized least squares estimation technique. The estimation quality is evaluated using statistical analysis, and the existence of damping coupling coefficients and, inertial coupling coefficients is discussed. The effects of initial eccentricity, oscillation frequency and oscillation amplitude on the force coefficients are examined. New dependencies of the coefficients on oscillation frequency and amplitude are shown. This paper presents semi-empirical formulas with corresponding confidence intervals for the damping and inertial coefficients based on the estimation, results and analytical predictions. A comparison with theoretical predictions is made and favorable agreement is found. These results are of value for the prediction of the dynamic response of heal exchanger lubes, as well as squeeze film dampers in turbomachinery.

Force Coefficients for Open-Ended Squeeze-Film Dampers Executing Small-Amplitude Motions About an Off-Center Equilibrium Position

Fluid-film forces generated by squeeze-film dampers (SFD) in response to small-amplitude motions about an off-center equilibrium configuration are of considerable importance for stability analyses of rotating machinery employing SFDs with weak or no centering springs. This approach is the basis for calculation of linearized force coefficients obtained by subjecting the journal to small perturbations in velocity and acceleration. The analysis considers the fluid flow in an open-ended SFD due to small-amplitude motions of the journal center about the static equilibrium configuration. Simplified governing equations are derived from the full Navier-Stokes equations by order of magnitude tests. Approximate damping and inertia force coefficients for finite-length SFDs are derived by implementing a correction factor to the long SFD model solution. This finite-length correction is of extreme simplicity and shows excellent agreement with a numerical solution to the differential equations for the pressure including fluid inertia effects. The correction presented tends asymptotically, as the SFD L/D ratio approaches zero, to the existing formulae for the short SFD model.

A Thermohydrodynamic Solution of Pivoted Thrust Pads: Part III—Linearized Force Coefficients

This is Part III, of a three-part sequence of papers on pivoted thrust pads. In this paper we calculate the linearized spring and damping coefficients of pivoted pads. Both the stiffness and the damping are shown to be strongly influenced by the degree of crowning. Spherical crowning is employed here to simulate pad deformation under the combined action of pressure and heat.

Paper 9: Linearized Force Coefficients of a 110° Partial Journal Bearing

Paper 9: Linearized Force Coefficients of a 110° Partial Journal Bearing