Abstract
The reliability of propulsion shafting systems is a major concern for ocean-going vessels because mid-ocean repairs can be time-consuming and spare parts must be available. To address this concern, vibration modeling and experimental measurements were conducted on a propulsion shafting system with a Z-drive propeller, with the objective of identifying the source of failure for the flexible rubber coupling connecting the diesel engine with the intermediate shaft. The torsional fluctuations in the flexible coupling dramatically increased and then abruptly ceased. The modeling results revealed that the frictional losses during power transmission through the universal joints could act as an excitation force for self-excited vibration. The coupling connected to the intermediate shaft did not have sufficient radial flexibility to dampen these vibrations. To avoid the effects of the self-excited torsional vibration, it is recommended that this coupling is replaced with one that is capable of absorbing the radial shaft displacement.
Highlights
Certain marine propulsion applications require efficient maneuverability under extreme conditions. One solution for this issue is the use of a Z-drive propeller, which may rotate freely to alter the direction of the thrust applied to the vessel
Lee et al investigated the unstable torsional vibration resulting from the friction torque that occurred in a propulsion shafting system [10]
The torsional vibration analysis identified that the resonant point was located on the flexible rubber coupling, which was employed to transmit the torque from the electric motor to the intermediate shaft and reduce the influence of the motor assembly on the propeller components
Summary
Certain marine propulsion applications require efficient maneuverability under extreme conditions. Lee et al investigated the unstable torsional vibration resulting from the friction torque that occurred in a propulsion shafting system [10] They observed that in the operating mode wherein the shaft generator is separated, the clutch should be entirely disengaged. The self-excited torsional vibrations (SETVs) were oscillating at a frequency of 3.75 Hz, similar to the shaft generator’s idle running speed (220–250 r/min) [11] In another experiment, torsional vibrations developed in an electric system equipped with an inverter motor to drive a propeller [12,13]. The torsional vibration analysis identified that the resonant point was located on the flexible rubber coupling, which was employed to transmit the torque from the electric motor to the intermediate shaft and reduce the influence of the motor assembly on the propeller components This resonance added to the increased dominant vibration at an approximately identical frequency.
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