The abundant research on the torsional vibration of propulsion shafting system have been reported, but a research on shafting system of a generator driven diesel engine has hardly been reported. The reason is that a generator driven diesel engine is driving at a constant speed differently from that of the propulsion engine, therefore it seems to be unnecessary to consider deeply the torsional vibration condition of the generator shaftings as of the main engine at the design stage. However, due to increase of the power of engine, being compact of generator and improving ofperformance, the torsional vibration of a generator driven diesel engine is increasing. It causes the excessive additional torsional stress on the shafting system, which lead to the break-down of the shaft. Consequently it become necessary to exactly analyze the torsional vibration of the generator shafting and estimate the safety of the relevant shafting system.
In general, the natural frequency of the generator shafting is analyzed using a equivalent mass-elastic model. As a generator shafting has the long keyed armature shaft, the natural frequency varies significantly according to the modeling methods for transferring the stiffness of generator shafting to equivalent mass-elastic system.
Therefore, in this study the adequate modeling methods for assessing the determination of stiffness of the long keyed armature shafts is firstly investigated. Also these methods are applied to shafting system of a generator driven diesel engine for analyzing of natural and forced torsional vibration in whole operating range using the transfer matrix method. As the measurement of forced torsional vibration of diesel engine coupled to generator was conducted at no load conditions, torsional vibratory amplitude was analyzed in view of the ratios of excitation force for diesel engine. It was confirmed from the analysis that the exciting force when the measurement of forced torsional vibration of diesel engine coupled to generator was conducted at no load condition is 15%.
And the method for transforming the vibratory amplitude measured at the fore-end of crankshaft to the additional stress of the shaft with nodal point was presented. The reliability of the computer program used in this study was confirmed by comparing the measured with the calculated results for the torsional vibration of the generator shafting.