Torsional vibrations lead to oscillations in the electromagnetic torque, too. These may dampen the vibrations, but they may also do the exact opposite.

Electric Motor Design, plus stuff
Torsional vibrations lead to oscillations in the electromagnetic torque, too. These may dampen the vibrations, but they may also do the exact opposite.
Of mechanics in electrical machines, torsional vibrations are often the most critical. Read here to learn the basic principles, and how to analyze them.