A bent shaft and a bowed rotor are actually the same phenomena. The bent shaft is measurable outside the machine housing while the bowed rotor is the same condition inside. The best protection against a bent shaft or bowed rotor is not to let a motor, or any machine with significant rotor weight, sit stationary for any length of time. The next best protection is to measure for a bent shaft before installation and not accept those motors with more than 0.001 microns in run out.
This experiment shows how the bent shaft increases the vibration levels of a rotating systems. Equipments can be done in the two modules, vig, a shaft without bend and a shaft with bend. The results of vibration measurements can be compared for identification of the bend shaft.