Research On Nonlinear Vibration Of Diesel Shafting Including Gas Forces

With cylinder, flywheel, propeller, nonlinearity of flexible wire rope couplings and their coupling system as the research objects, nonlinear dynamics problems of marine diesel shafting are studied by means of nonlinear vibration theory and numerical analysis method.The diesel shafting is modified to two-disk system, the differential equation is derived by means of Lagrange equation. Applying the method of multiple scales to the nonlinear vibration, the approximate solutions of primary resonance, 1/3 subharmonic resonance, 3 superharmonic resonance and primary parameter resonance of the system are obtained, numerical results of the influences of excitation, detuning and damping on the system are analyzed in detail. SIMULINK model is established on the basis of differential equation to get time history curve and phase portrait curve. The results are compared with the results of the method of multiple scales. In primary resonance, 1/3 subharmonic resonance and 3 superharmonic resonance, the excitation K sin( nθ1 +φ) is considered as n =1 and n≠1. Jumping phenomenon occurs to amplitude frequency response curve of primary resonance; 1/3 subharmonic resonance doesn't exist within reasonable scope of excitation; There are two branches in the amplitude frequency response curve of primary parameter resonance.The diesel shafting is modified to three-disk system, and both gas forces of the cylinder and hydrodynamics of the propeller are the excitations of the system, the differential equation is derived by means of Lagrange equation. Considering the rotating of flywheel as uniform speed, equation groups without coupling terms are got, considering the rotating of flywheel as variable speed, equation groups with coupling terms are got. Equation groups without coupling terms are carried out as two single freedom systems: the former has been analyzed, the latter is analyzed in primary resonance, 1/3 subharmonic resonance and 3 superharmonic resonance. Equation groups with coupling terms are carried out as two conditions: frequency of excitation near to first order natural frequency and frequency of excitation near to second order natural frequency.