Coupled torsional and axial nonlinear vibration model of the crankshaft with a propeller

The nonlinear model of the crankshaft system with a propeller is established, in which the variable moment of inertia of the linkage and the piston, coupling effect between torsional and axial vibration, the actuating force applied on the piston, the actuating torque and force applied on the propeller is included. 6 linkages and pistons are involved in the model. The governing equations of the model denote a strong nonlinear and non autonomous system. By numeric calculation, the time history and frequency spectra of the system response at working speed are obtained. It is found that two times frequency component is significant in the relative torsional vibration spectrum between the propeller and the first crank, between the fifth and the sixth crank. In the relative axial vibration response, fundamental frequency, six times and twenty times frequency components are discovered. Four times frequency components are not discovered, with which, the actuating force is applied on the propeller. Therefore, more errors may be caused, if the propulsion system of the marine diesel is designed according to the linear vibration model.