Stability Analysis of Flexible Rotor Supported by Active Hybrid Bearing With Fuzzy Logic–Based Control

Abstract The classic film hydrodynamic bearing is a passive device, and its design does not consider the adaptive capacity to change with operation conditions. The film journal bearing coupling with servovalve, fuzzy proportional-derivative controller, and sensor, called active hybrid bearing with fuzzy logic-based control (AHBF), can accept controllable orifice flow to produce active force for reducing the rotor vibration and adapting to different operation demands. The AHBF is modeled as a couple of four parts: controller, servovalve, orifice flow, and film. The orifice flow is modeled as a series of a servovalve, capillary restrictor, and gap restrictor, considering the throttling effect of the servovalve, orifice tube, and film gap. The spool motion of the servovalve is modeled as a second-order transfer function and controlled by the fuzzy proportional-derivative controller. The feedback signal is the center displacement of the journal. The governing equation of film pressure is a modified Reynolds equation containing the orifice flow, which is linearized by the Newton–Raphson method and calculated by the finite element method to get the static characteristic. The results indicate that the proportional coefficient significantly affects the bearing load capacity. When the dimensionless load is between 0 and 0.6, the max increment of the minimum film thickness can be 271%. The dynamic coefficients of the AHBF are calculated using the orbit analysis method. The perturbation method is usually practical for analyzing the bearing dynamic characteristics, but is unreliable in large eccentricity tracks. In addition, the orbit analysis method can provide more reliable results for dynamic characteristics when bearing models are challenging to linearize. The influence of operating parameters on the dynamic characteristics of the AHBF is studied. The results indicate that the stiffness and damping of the bearing can be increased by up to 403% and 74% under active control operation by selecting an appropriate range of control parameters. The unbalanced response of the rotor with the transient oil film force is calculated in passive and active control operations. Compared with passive operation, the amplitude at the bearing can be reduced by 67% in active control operation. In conclusion, the AHBF has better static and dynamic characteristics than hydrodynamic journal bearing. Besides, the rotor supported by the AHBF has lower vibration than passive operation.