“Nonlinear Whirl Response Of A High-Speed Seal Test Rotor With Marginal And Extended Squeeze-Film Dampers,”
M. P. Proctor & E. J. Gunter, 2005.
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Synchronous and nonsynchronous whirl response analysis of a double overhung, high-speed seal test
rotor with ball bearings supported in 5.84- and 12.7-mm-long, un-centered squeeze-film oil dampers is
presented. Test performance with the original damper of length 5.84 mm was marginal, with
nonsynchronous whirling at the overhung seal test disk and high amplitude synchronous response above
32,000 rpm near the drive spline section occurring. A system critical speed analysis of the drive system
and the high-speed seal test rotor indicated that the first two critical speeds are associated with the seal
test rotor. Nonlinear synchronous unbalance and time transient whirl studies were conducted on the seal
test rotor with the original and extended damper lengths. With the original damper design, the nonlinear
synchronous response showed that unbalance could cause damper lockup at 33,000 rpm. Alford cross-coupling
forces were also included at the overhung seal test disk for the whirl analysis. Sub-synchronous
whirling at the seal test disk was observed in the nonlinear time transient analysis. With the extended
damper length of 12.7 mm, the sub-synchronous motion was eliminated and the rotor unbalance
response was acceptable to 45,000 rpm with moderate rotor unbalance. However, with high rotor
unbalance, damper lockup could still occur at 33,000 rpm, even with the extended squeeze-film
dampers. Therefore, the test rotor must be reasonably balanced in order for the un-centered dampers to
be effective.

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