Effect of Forcing Terms and General Characteristics of Torsional Vibrations of Marine Engine Systems with Variable Inertia

Abstract

The torsional vibration phenomenon in the running gear of reciprocating engine systems is usually dealt with by considering a series of constant inertias connected by sections of massless shafting. Such a simplified model does not reproduce the exact dynamic characteristics of the actual system. In recent years several cases of marine crankshaft failures have been attributed to the phenomenon of secondary resonance, which is explained by the fact that the effective inertia of each slider crankmechanism varies about a mean value in relation to the position of the crank. When the variableinertia effect is allowed for, the equations of motion taking into account the effect are nonlinear. Assuming small displacements, the equations can be linearized to predict important characteristics of the motion. The motions in the form of complex wave forms are studied at different speeds of engine rotation and some of the wave form solutions are analyzed in the range of present investigations. Computer methods making use of numerical analysis processes, namely, the modifiedEuler's equations and the Runge-Kutta constants, have been applied in the investigations. A study of the effect on the motion of the system due to variation of inertia ratio is carried out at a particular speed of the crankshaft rotation; also investigated are the variations in the motions due to the action of external excitations with respect to changes in phase angle and inertia ratio. General comments on Draminsky's work in the light of the present investigations are included.