A Computational Model for the Analysis of the Static Forced Performance of Self-Equalizing Tilting Pad Thrust Bearings
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AbstractWhile failure analyses in the archival literature report thrust collar misalignment as a major cause of collapse in oil lubricated thrust bearings, a self-equalizing tilting pad thrust bearing (TPTB) improves operation reliability by adjusting its pads to account for thrust collar tilt. The paper describes a kinematics model for the equalizing mechanism integrated into an existing thermo-elasto-hydrodynamic (TEHD) analysis tool to deliver load performance predictions for self-equalizing TPTBs. The analysis considers the actual leveling plates geometric model as obtained from a solids modeling commercial software and accounts for the sliding friction forces acting at the contact points of the leveling plates and the rolling friction at their pivots. Further, a Hertz contact analysis model uses the predicted forces to deliver a peak pressure and deformation over the contact area between the leveling plates. Next, the paper presents predictions for an example self-equalizing TPTB operating with a thrust collar static misalignment = 0.01. The bearing 126 mm in outer diameter has six pads, operates at 4 krpm (26 m/s max. surface speed) and under a specific load/pad ranging from 0.5 to 3.5 MPa. Compared to a non-equalizing TPTB, a self-equalizing TPTB operates with up to 50% larger minimum film thickness and about largest elastic deformation. Friction forces acting at the contact points of the leveling plates show a significant effect on the performance of the pad leveling system as they reduce the film clearance and increase a pad peak pressure. Predictions from the Hertz contact analysis agree with those from a commercial finite element analysis tool and show a significantly large peak pressure at the contact points of the leveling plates (< 0.9 GPa) when the bearing supports a 3 MPa/pad specific load. The paper stresses the importance of conducting a comprehensive multiple-pad analysis to accurately evaluate the performance and reliable operation of self-equalizing TPTBs.
