Hydrodynamic oil film bearings exhibit lateral flexibility which
influences the dynamics of rotors they support. This lateral flexibility is specified by coefficients which relate forces generated by
the oil film to the instantaneous journal centre velocity and its
displacement from an equilibrium position. Previous investigators
adopted a linear treatment by taking uniform viscosity with small
displacement and velocity increments. Relatively large journal
centre velocities are possible in rotating machinery. Therefore,
this thesis investigates the non-linear behaviour of these oil film
coefficients.
Coefficient calculations allowed viscosity to vary with temperature
and pressure rendering the governing Reynolds Equation non-linear.
A range of positive and negative displacement and velocity increments
were examined. Novel experimental techniques have been developed
which allow determination of coefficient variation with respective
displacement and velocity. Coefficients were deduced from specially
chosen, imposed vibration orbits arising from two mutually perpendicular
external oscillating forces of variable relative magnitude and phase.
Journal centre displacement and velocity were measured using high
speed data logging equipment. A unique feature was the ability to
obtain, experimental displacement coefficients from the results of both
dynamic and incremental loading. It was found necessary to establish
the bearing centre separately for each warm-up/load combination.
Journal clearance in the hot rotating condition could not be measured
to the precision required by its sensitivity to calculated load.
Clearance and cavitation zone pressures were deduced from simultaneous
predictions of the measured vertical load and attitude angle.
Theoretical oil film tensile forces were necessary, a proposition
supported by recently published experimental findings. Theoretical
results for an equivalent uniform viscosity combined with experimental
data gave a simple static locus design procedure. A temperature
profile was assumed for theoretical work but choice thereof was found
to be not critical.
Coefficients are defined in terms of a "zero" value and linear gradient.
Using realistic criteria, measured coefficient variation was found to
be significant at eccentricity ratios greater than 0.78. Theory
adequately predicted most "zero" values but not gradients. It is
concluded that improvement in the coefficient prediction willPh
