Abstract: Aimed at the nonlinear vibration problem caused by multi-source excitation in hydraulic generating set shaft systems, a coupled bending-torsional vibration model for the shaft system under the combined action of its unbalanced magnetic pull and nonlinear sealing force considering both dynamic and static eccentricity factors is developed, and numerical simulations are used to investigate its dynamic characteristics. This paper analyzes the effects of mass eccentricity and sealing clearance on its vibration behaviors using nonlinear analysis methods such as bifurcation diagram, axis trajectory diagram, and spectrum diagram. Results show that dynamic and static eccentricity of the shaft system poses a significant impact on its dynamic characteristics and amplitudes, and improves its stability to a certain extent, where new dynamic phenomena such as period-three and period-six modes appear. Mass eccentricity will weaken the effect of its unbalanced magnetic pull while aggravating its rotor vibration, resulting in its more regular motions; but excessive mass eccentricity is bound to cause the full annular rubbing of the unit, which is likely to provoke potential system instability. A larger sealing gap can reduce the damping and friction of the shaft system and help stabilize its movement, but an excessively large gap will increase fluid leakage and reduce the operating efficiency of the hydraulic generating set.

Key words: rotor-running system, dynamic and static eccentricity, unbalanced magnetic pull, nonlinear sealing force, coupled bending-torsional vibration