Effect of Gas Forces on Parametrically Excited Torsional Vibrations of Reciprocating Engines

In the past the effects of ignoring the variable inertia characteristics of reciprocating engines on the accuracy of torsional vibration calculations were considered to be negligible. The associated secondary resonances tended to be dismissed by most engineers as interesting but of no importance. The situation changed in recent years, since there was evidence of the existence of the secondary inertia effects, which could have contributed to a number of otherwise inexplicable crankshaft failures in large multi-cylinder marine diesel engine systems. In view of these facts, a mathematical model is derived with key nondimensional parameters for the analysis of the effect of gas forces on the motion of the variable inertia system. The complex waveform responses are examined in detail within the range of speeds of engine rotation at which adverse effects are known to have occurred in practice. The effects on the parametrically excited motion of the system are investigated at a particular speed of the crankshaft rotation due to the action of external excitations with respect to changes in phase angle and inertia ratio. It is shown that under certain circumstances, interaction of secondary resonance effects with the excitations can be serious for torsional vibration. General comments on Draminsky's work in the light of present investigations are included.