Recently, the axial stiffness of marine diesel engine crankshaft has decreased due to super long stroke application, and the mass of crankshaft has increased due to high supercharging. These have frequently resulted in the appearance of axial vibration for propulsion shafting in maneuvering range.
It is evident that axial stiffness and mass of crankshaft, thrust block stiffness, propeller's entrained water, and exciting and damping forces are primary factors which affect axial vibration of propulsion shafting.
In this paper, the theoretical formulae for calculating axial stiffness and transfer factor of axial to radial force for crankshaft were derived. The former was checked by comparing results of measured values of three actual crankshafts. The obtained results were also compared to those of 5 formulae previously derived by others. In addition, the axial damping force was also analyzed.
Based on calculation results, the natural frequencies and resonance amplitudes of axial vibration for propulsion shafting on two ships were calculated and compared with measured values.
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