Calculation of the Torsional Vibration in Marine Shafting System with Nonlinear Component

Abstract

Where the torsional vibration in a marine propulsion system with reduction gears is calculated, it is usually assumed that the gear assembly is torsionally rigid, i.e. the torsional rigidity of tooth and gear backlash are neglected. With regard to the turbine-propulsion installations, however, especially during astern maneuvering, the gear tooth does not always keep the contact with each other. Then it is necessary to take into account of nonlinear behaviour due to gear backlash combined with torsional rigidity of tooth for the calculation of the torsional vibration.
In this paper, the turbine-propulsion installation is simulated as a 5-masses gear-branched system with gear backlash.
The calculation of the above system is carried out by the use of hybrid computer. The effect of the mass moment of inertia in the free running branch, the damping coefficient of the lubricating oil film between gear teeth and the amplitude of the excitation propeller torque to the vibrating torque in shafts and the impact loads at gear teeth are quantitatively obtained. Where the 2nd natural frequency is far away from the 1st one, the hysteresis phenomenon appears and at the same time the random impact loads at the gear tooth occur on free running branch. On the contrary, where the two natural frequencies are close, the hysteresis phenomenon does not appear and the vibrating torque in the shaft of the free running branch is strongly suppressed by the other branch which acts such as a dynamic damper.