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The independent effects of e.rcitation frequency and escitariorr n~agnitltde on esperin~entally derived hearing coeficier~ts for a highly preloaded three-lobe jo~rrnal hearing were studied. The effect of escitation fieq~ret~cy was determined by applying e,~ternal dynamic forces at half-synchronous, synckrono~ts, and twice synchronorrsfrequencies with respect to the operatitlg speed. Effect of e,vcitation nlcrgninrde ~l a s independently deternzirled by applying either three or forrr dtfferent an~plitudes of e.vcitatiort force to the hearing resulritrg in orbit sizes ranging tip to 30% of clearance. Applying static forces to the hearing housing controlled the Somniet$elrl nrm~her, and thus, the static operating position. Data Presented as a Society of Tribologists and Lubrication EngineersPaper at the STLEIASME Tribology Conference in San Francisco, CA October 21-24,2001 Final manuscript approved June 12,2001 Review led by Gregory Kostrzewsky was reduced as linear dynaniic coefficients, and presented relative to excitation frequency and excitation niagtiilude over a range of Sonlnlerfeld numbers from 0.2 to 3.0 and operating eccentricities from 0.3 to 0.9. In general, neither excitation frequency nor e.rcitatioti magttitrtde was shown to have a nieasurahle efSEct over the ranges studied.

To validate a new squeeze film damper (SFD) bearing design introduced in [1], a pair of 3.5 inch SFD bearings were manufactured and tested. Static spring compression test was conducted to prove the spring design stiffness calculated through the geometry parametric spring model. High cycle loading fatigue testing of the spring was conducted to validate the design spring fatigue limit. The entire SFD bearing assembly was inspected and checked through a SFD centering bench test before the rotor dynamic test. Unbalance response correlation and logarithmic decrement (Log. Dec.) measurement using the operational modal analysis (OMA) method were employed for the rotor-dynamic tests. An agreement was seen between the analysis and the experimental measurement. It was seen that the SFD bearing provided the extra damping as expected to suppress the unbalance vibration when passing through the critical speed and also improve the stability (Log. Dec.) of the rotor. It was found that the measured SFD damping was closer to the full film damping model when the squeeze oil film was sealed with O-rings. The SFD improved the logarithmic decrement of the rotor-bearing system from 0.07 to more than 0.21 as compared to the system without SFD.