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Rubbing dynamics behavior of a flywheel shafting with a single point flexible support
Author: Tang Changliang | Print | Close | Text Size: A A A | 2018-11-30

The flywheel energy storage system is a new kind conversion device which realizes electric energy and kinetic energy transform into each other. The dynamic characteristics of flywheel energy storage system have been studied extensively in recent years. A single point flexible support is suitable for the small flywheel system, because the friction loss is very low. The flywheel spin test system with a single point flexible support was built. The dynamic model of the flywheel shafting was established to calculate the critical speeds, modal shape and modal damping ratio at different speeds. The results show that the dynamic characteristics of the flywheel shaft are stable, and its structure is simple and efficient. The comparison between the calculated unbalance response and the experimental response indicates that the dynamic model is appropriate. When the flywheel started up and rotated at different speeds, the rubbing dynamics behavior was obtained by the experiment. Full rubbing occurred at high speed would damage the flywheel and stop, which should be tried to avoid.

Conclusions

1) The lower support of the flywheel shafting was composed of pivot jewel bearing and oil damper. The stiffness of pivot was very small. The oil damper provided viscous damping for the flywheel shafting. The stop at the flywheel top was used to start up by rubbing. The dynamic model of the flywheel-bearing-damper system was built by means of the Lagrangian equation. The Campbell diagram, critical speeds, mode shapes, and modal damping ratios were calculated at different speeds. The numerical simulation indicated the exchange of mode shapes occurred in a narrow frequency range was a new kind of dynamic characteristics produced by flexible damping support. Through the analysis of the modal damping ratio, the dynamics of the flywheel shafting system was stable when the stop acted or not.

2) The comparison between the calculated unbalance response and the experimental response indicates that the dynamic model is appropriate. The experiments on the flywheel/stop rubbing demonstrated that the stop suppressed the low-frequency whirl successfully when rubbing to start up. The flywheel/stop rubbing was to make shafting rotating steadily. The bigger gap had the longer time for rubbing to start-up. The shorter rubbing time will also reduce the damage to the stop and flywheel rotor. It was necessary to choose a smaller gap in the test. The certain external harmonic excitation force was used to simulate the low frequency produced by sudden unbalances. In the very wide speed range, the low external harmonic excitation made the flywheel shafting produce period 1, period 2 bifurcation, period N and quasi-period motions. When the low-frequency excitation was cancelled, the flywheel shafting could resume stable operation and had not low and high frequencies except rotating frequency.

3) When the exciting force exceeds a certain value at high rotating speed, the quasi-periodic motion will change to chaos motion, and then the full rubbing occurs with continuous collision and friction inside the gap. The center of flywheel rotor moves counter-clockwise, and the whirl amplitude exceeds the gap unexpectedly. Moreover, the rubbing frequency is much higher than that of the excitation and the unbalance force. The rotor rotation is broken quickly by the stop. The full rubbing should be prevented since it damages the flywheel and stop directly.

The results have been published on JOURNAL OF VIBROENGINEERING. SEP 2017, VOL. 19, ISSUE 6. ISSN 1392-8716.

 

 
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