| Experimental and theoretical results are presented for the rotordynamic coefficients of a four-pocket oil-fed orifice-compensated hydrostatic journal bearing, including the hybrid effects of journal rotation. The test aparatus incorporates a double-spool-shaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular orbit, for both forward and backward whirl. This configuration yields data that enables determination of the full linear anisotropic rotordynamic model. The dynamic force measurements were made simultaneously with two independent systems, one with piezoelectric load cells and the other with strain gage load cells. A computer code based on a finite-difference solution of Reynolds lubrication equation was used to make theoretical predictions for the same configuration and operating conditions as the test matrix. The computational results agree well with test results, theoretical predictions of stiffness and damping coefficients are typically within 30% of the experimental results. For all conditions, statically centered as well as eccentric, the rotordynamic coefficients are close to isotropic. Software was developed for the high speed data acquisition and analysis of the rotordynamic coefficients in different data reduction modes, including allowed frequency dependence. The coherence functions were calculated to relate the time-averaged x and y input motion signals and the x and y time-averaged output force signals. This gave rise to four coherence functions, {dollar}gammasbsp{lcub}rm xx{rcub}{lcub}2{rcub},{dollar} {dollar}gammasbsp{lcub}rm xy{rcub}{lcub}2{rcub},{dollar} {dollar}gammasbsp{lcub}rm yx{rcub}{lcub}2{rcub}{dollar} and {dollar}gammasbsp{lcub}rm yy{rcub}{lcub}2{rcub}.{dollar} In all test cases, these coherence functions were between 0.999 and 1. |
