Study On Nonlinear Vibration Of Large Hydropower Units

Studying on the theoretical background of nonlinear rotor dynamics to a large hydropower generating units, this paper can simplify physical model of the unit and the establishment of a lateral vibration free motion equation, solve the unit lateral vibration natural frequency and modal. The electromagnetic rigidity for the natural frequency of the impact is analyzed. At the same time, a rotor in a non-linear effect of unbalanced magnetic pull-lateral vibration equations of motion runner systems is established. Static eccentric rotation of the eccentric, speed and upper guide bearing stiffness for nonlinear vibration characteristics of electromagnetic effects crew are analysed. Finally a rotor in nonlinear oil film force and nonlinear interaction of unbalanced magnetic pull-vibration equations of motion transverse bearing systems is established, analysis the rotor eccentricity, speed and bearing clearance for vibration characteristics of the system’s impact, and the difference between the traditional linear oil film force and the nonlinear oil film force are analysed.Studies have shown that the first six natural frequencies are f1 = 2.737, f2 = 5.045, f3 = 19.31, f4 = 47.04, f5 = 129.4,f6 = 176(Hz). Electromagnetic stiffness only affect the first two natural frequencies unit shaft, Thinking of 100 percent of the electromagnetic solenoid stiffness which is not considered first-order and second-order natural frequency decrease by about 7% and 11%. Static eccentric presence can affect the trajectory of the rotor, causing it to render in 8-shaped trajectory. And the vibration amplitude increases with the static eccentricity. when the static eccentricity amount is 0.1mm, amplitude spectrum appears at 2 octave. Changing the guide bearing stiffness can significantly affect the rotor amplitude-frequency characteristics. Along with the magnitude of the upper guide bearing stiffness increasing multiples of the rotor 1 is significantly reduced, and the vibration amplitude at 2 octave is much lower. With the speed of the vibration increasing amplitude of the unit will significantly increase, the trajectory will gradually become complicated, and it gradually change from periodic motion into the quasi-periodic even chaotic state. While a large number of low-frequency harmonic will be componented with the speed. With bearing clearance increasing, radial displacement of the rotor will also increase. And it will from Cycle 6 moved into a quasi-periodic motion, a small amount of low-frequency harmonic component appears. At magnitude of 1.5 multiplier there are a large amout of lowfrequency harmonic componet. Although nonlinear oil film force or linear oil film force is different from the impact on the rotor radial amplitude. With respect to the state of motion trajectory or amplitude-frequency characteristics, the influences are quite obvious.