Various parameters influence the measured and predicted stiffness and damping of tilting pad journal bearings. This research consists of both measured and predicted dynamic response over a range of Sommerfeld numbers and preloads. The preload range is from 0.5 to −0.333. The Sommerfeld range is from 0.0899 to 4.529. An investigation of the dynamic characteristics subject to variables such as: pivot type, excitation frequency, preload, and Sommerfeld number is presented. Three unique areas are addressed in the work presented. Because of tolerance and wear many tilting pad bearings operate in the negative preload regime. The measured dynamic coefficients were used to calculate the instability onset speed of the rotor. For positive preload bearings the instability onset speed was found to be infinite. However for negatively preloaded bearings with Sommerfeld numbers greater than 0.8 a bounded stability level was found to exist. This work also established the measured validation of predicted dynamic bearing properties in the negative preload regime. The influence of pivot type on the dynamic behavior of bearings is also presented. For the spherical ball and socket pivot bearings below a Sommerfeld number of 0.8 the cross coupled stiffness terms were the same sign, above that Sommerfeld number the cross-coupled stiffness terms were opposite in sign. The rocker-backed bearings tested showed no statistically significant levels of cross-coupling. Tilting pad bearings are also inherently dependent upon excitation frequency. Measured dynamic coefficients are shown to exhibit the same trend as predicted.
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