Experiment of oil-film stiffness and composite support stiffness of thrust bearing in marine propulsion shafting

In marine propulsion shafting, the stiffness of the thrust bearing depends on the oil-film stiffness, structure stiffness of the bearing and its base. And, the thrust bearing stiffness only includes the oil-film stiffness. So in this paper, the comprehensive stiffness including both the oil-film stiffness and the bearing and its base structure stiffness is defined as the composite support stiffness. The method of measurement for the oil-film stiffness and the composite support stiffness is investigated and then the experiment is carried by this method in a scaled thrust bearing test board. The good experiment results are obtained. It shows that the oil-film stiffness decreases as the rotational speed rise. The composite support stiffness decreases as the excitation frequency rise and is equal to zero in the base resonance frequency. The oil-film stiffness and the composite support stiffness are approximately equal in low-frequency excitation. Then only the oil-film stiffness may be considered in the dynamic model of the shaft. The composite support stiffness is considerably larger than the oil-film stiffness in high-frequency excitation. Then the composite support stiffness must be considered in the dynamic model of the shaft and it brings big errors only to consider the oil-film stiffness. These conclusions can provide a reference and guidance to the design and dynamic analysis of marine propulsion shafting.