engleski

Experimental Determination of Stern Tube Journal Bearing Behavior

The most sensitive component in the propulsion shafting system is the aft stern tube bearing, which is exposed to heavy static and dynamic propeller loads exerted to the bearing surface by the propeller shaft. The Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, and the American Bureau of Shipping intend to work on the development of the theoretical model of the stern tube journal bearing behaviour, which is proposed to be done in several stages. The initial stage is to consider nonlinear fluid structural interaction, and this is the theory shown in this article. Owing to the fact that the shaft journal in operation lies on a lubricating fluid film, which separates the journal in the bearing from the bearing liner, the theoretical nonlinear model of the journal bearing may provide more insight in the behaviour of the shaft inside the bearing and help us to determine a more realistic elastic line of the shafting. The American Bureau of Shipping (ABS) initiated a research project to measure actual interaction between the shaft and the stern tube bearing with the goal of applying obtained knowledge in development of an accurate analytical/numerical model for shaft-bearing analysis. The initial focus of the investigation was to capture the transient operation of the shaft inside the bearing and to observe the shaft's hydrodynamic lift during starting, stopping and reversing of the engine. Proximity probes were used to monitor the shaft bearing interaction with micron precision. The installed probes measure the distance between the shaft and the bearing at eight locations inside the aft stern bush and at four locations inside the forward stern bush, and utilize obtained data to define the shaft orbit and dynamics as it revolves in the bearing. The results of presented measurements show that the shaft behaviour inside the stern bush is very different depending on the location inside the bush. Therefore, an analytical approach, which uses a simplified theory of shaft bearing interaction, provides no practical value since it neglects shaft dynamics and interaction between fluid and the structure.

Propulsion shafting system; Stern tube bearing; Shaft Alignment; Proximity Sensors; Alignment Condition Monitoring; Nonlinear model of radial journal bearing

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