Abstract
Because a marine steam turbine propulsion shafting contains some gear trains which run idling at the transient condition such as astern operation, it is well known that the peculiar torsional vibraton phenomena with gear teeth chattering at the crash astern operation, etc.
The author has considered that this phenomena is caused by not only the existing of the gear backlash but also the effect of the bearing oil film which results in self-exciting vibration. And he made a mathematical model of the propulsive shafting system including the gear backlash combined with the bearing oil film of the pinion gear in order to clarify this phenomena.
By computer simulation using this mathematical model, it is concluded that the self-exciting vibration occurs at a certain shaft RPM due to the bearing oil film which gives an effect to such a peculiar torsional vibration as has a certain frequency unrelated to the number of the propeller blade and it can be explained well by this model.
