Journal Bearing With Controllable Radial Clearance

Abstract

This work presents the novel design of a smart hydrodynamic journal bearing with adjustable radial clearance. The dynamic behavior of this bearing was mathematically modeled and examined. Finite Element Analyses were conducted to determine the effort needed to change and maintain a desired value for the radial clearance. First, the bearing set was modelled as a two-degrees-of-freedom dynamic system. For an initial value of a radial clearance of c = 0.0508 mm, the bearing set exhibited an unstable behavior under its postulated operating condition. A Generic Algorithm (GA) was used to define an objective function so that an optimum value of c could be determined in order to ring the bearing into a stable operating condition. The GA determined the value of radial clearance of c = 0.0051 mm for this purpose. Second, a Jeffcott rotor was modeled as an eight-degrees-of-freedom vibratory stem supported by two identical smart bearings. For an initial value of c = 0.025 mm, the disk’s peak-to-peak vibrations amplitude was determined to be 8 × 10−5 meter and 8.5 × 10−5 m along two orthogonal axes of a reference frame respectively. The GA was used to determine a new value for the radial clearance of the supporting bearings in order to reduce the disk’s vibration level. A new value of radial clearance c was determined to be 0.095 mm which in turn reduced the vibrations of the dick from 8 × 10−5 and 8.5 × 10−5 meter to 3.5 × 10−5 and 2.5 × 10−5 m respectively.