Rotor‐Bearing System Stability Performance Comparing Hybrid versus Conventional Bearings

New closed-form expressions for calculating the linearstability thresholds for rigid and flexible Jeffcott systems andthe imbalance response for a rotor supported on a hybrid bearingare presented. For typical bearings characteristics, expressions yield stability thresholds practically equal to those reported byLund (1966). The hybrid bearing design has a single injectionport whose location is so chosen to stabilize the bearingperformance and to reduce the steady equilibrium attitude angle.Rotordynamics coefficients graphs for conventional andpressurized bearings, as functions of bearing equilibriumeccentricity and/or Sommerfeld number, are presented. Using therotordynamics coefficients into the expressions for thecorresponding velocity thresholds and the imbalance response, thesystem stability and vibration performances are estimated andanalyzed. When comparing the Jeffcott flexible shaft supported ontwo journal bearings of the conventional type with the hybridtype, the results show a clear superiority of the pressurizeddesign as far as stability behavior is concerned. Specificallyfor cases of flexible shafts with similar characteristics tothose used in industry, the analysis shows that this design yieldsvelocity thresholds 25%–40% higher compared to theconventional circular ones. Also this bearing displays nonlinearfeeding pressure behavior, and it is capable of reducing thesynchronous vibration amplitude in most speed ranges, exceptaround the critical speed; moreover, for certain Jeffcottconfigurations the amplitude reduction can be substantial