Simulation Method of Torsional Vibration Waveform of Reciprocating Engine Crankshaft Systems by Transition Matrix Method

Abstract

Abstract The torsional vibration of the crankshaft system of high speed diesel engines has become more excessive with the increase of engine power and with the decrease of engine rigidity. So it is necessary in the design stage to improve accuracy in the calculation of maximum torsional vibration amplitude at resonant engine speed. At first, this paper refers to a method for obtaining experimentally engine damping that is necessary for the calculation of torsional vibration. If the value of the damping cannot be accurately estimated, the accuracy of the calculated result is still not satisfactory. In this experiment, the decay constant is obtained from the record of the damped, free torsional vibration waveforms which can be got by stopping abruptly combustion in steady operating. It is also shown that the damping ratio, which is approximately 0.03 to 0.04 in high-speed, small diesel engines, can be got from the already-obtained decay constant. Secondly, authors try to calculate directly resultant amplitude by using a step by step transition matrix method. The simulated waveforms of torsional vibration of a high speed diesel engine are compared with the experimental results and it is shown that the calculated results by the transition matrix method are accurate. At the same time, this paper refers to a method for the estimation of engine damping coefficient that is necessary for the calculation of torsional vibration. In this method, the damping coefficient can be got from the previously obtained damping ratio.