TORSIONAL VIBRATIONS IN RECIPROCATING ENGINES

In the case of reciprocating engines, there are certain critical speeds of running at which the torsional vibrations in the shaft become large in amplitude and introduce an element of danger into the system. Fairly simple methods have been devised for the practical calculations to predict the torsional vibration characteristics from the constants of the machinery. The torsional vibration phenomenon in the running gear of reciprocating machinery is usually dealt with by considering a series of constant inertias connected by sections of massless shafting. In recent years several cases of fractures in the crackshafts of large marine engines have been attributed to the phenomenon of secondary resonance, which is explained from the fact that the effective inertia of each slider-crack mechanism varies about a mean value in relation to the position of the crank. Simplified theories predicted these designs of diesel engines as safe in practice. In view of the importance of the subject of torsional vibrations in engineering practice, the effects of variation in inertia on the torsional vibration of the system are examined in detail in the present paper. A comparison of theoretical results with Goldsbrough's experimental results is included.