On the Torque-fluctuation of intermediate Shaft

Abstract

The present paper gives the records of torque-fluctuations of the intermediate shaft measured by the Author's torsion-meter on the sea trials of merchant ships, and deals with some qualitative analyses of them. The shaft horse-powers of 64 ships, whose normal powers ranged from about 3, 000 to 10, 000 S. H. P., were measured by us during the past 6 years, and in the present paper the records of 27 ships are taken as their representatives. The records for oil tankers are harmonically analysed.The principal results obtained are summarized as follows:1. The torque-fluctuations of intermediate shafts are caused by the unbalanced torques of drivers and periodic resisting torques of followers.2. The unbalanced torques of reciprocating engines interfere with the periodic resisting torques of propellers, so, for example, in the case of four-bladed propellers, it seems to be practically, possible to reduce the 4th order vibrations of shaftings by arranging propeller blades and cranks at suitable phases.3. In the case of turbine ships, only the periodic resisting torques of propeller and reduction gears should be considered in connection with torsional vibrations.4. The violent vibrations with one node can be seen at the shaftings with shorter intermediate shafts, owing to the higher frequencies of free vibrations of one node.5. Assuming the positions of nodes of forced vibration to be the same as those of free vibrations, the amplitudes of the vibrations and the distributions of stresses of shaftings can be computed from the records of torque-fluctuations. Therefore, the Author's torsion-meter may be said to be an inertialess torsiograph.6. The distributions of stresses thus obtained give the data available for the design of shaftings.7. Since, in general, propellers are situated at the loops of all modes of vibrations of shaftings, the fluctuations of angular velocities of propellers can be computed from the records of torque-fluctuations. And also the fluctuations of torques and thrusts of propellers due to those of their angular velocities can be found.8. The torques of intermediate shafts are the sums of the inertia torques of the virtual mass of propellers and hydrodynamical torque of propellers. Therefore, the effects of torque-fluctuations of intermediate shafts should be considered for designing propellers. 9. It is natural that the torsional vibrations of shaftings cause the lateral vibrations. Therefore, they must be considered the sources of other vibrations.10. The approximate values of the rates of torque-fluctuations at 3/4 loods of engines are as followes:-±2%_??_±9%, for turbines, diesel engines with hydraulic couplings, steam reciprocating engines with low pressure turbines, etc.±8%_??_±20%, for diesel engines with longer intermediate shafts.±30%_??_±50%, for diesel engines with shorter intermediate shafts.±160%, for the steam reciprocating engine dealt with.