A Study on the Unstable Vibration Phenomena of a Reduction Gear System, Including the Lightly Loaded Journal Bearings, for a Marine Steam Turbine

Abstract

Rotatory machines such as turbines and compressors, almost invariably, include several power transmission gears. The relation between the torsional vibration and the gear transmission mechanism supported by the oil-lubricated journal bearings, however, has never been elucidated. The unstable vibration phenomena (different from ordinary phenomena such as oil whirl, oil whip and so forth) were observed in the locked train type reduction gear system of a marine steam turbine while it was subjected to running conditions with no load. The unstable vibration phenomena are assumed to be due to the self-exciting vibration system which is caused by both the oil film characteristics of the journal bearings which support the reduction gears and the torsional vibration system. The results of the calculations using a dynamic model provide a satisfactory explanation of the phenomena. According to the authors' research, the unstable vibration phenomena are strongly influenced by the torsional rigidity of the system.