Vibration of a rotating shaft with randomly varying internal damping

A simple Jeffcott rotor is considered with both external and internal damping. Coefficient of internal damping is subject to temporal random variations which may occasionally bring the rotor into the domain of dynamic instability. The corresponding sporadic outbreaks in the rotor's vibrational response (whirl) are studied by applying the Krylov-Bogoliubov averaging method to the complex equation of motion and using parabolic approximation for the random coefficient of the internal damping. This results in an explicit analytical solution for the radius of whirl which may be used for predicting reliability of the rotor. Furthermore, a convenient procedure is described for interpreting measured on-line test data for the rotor. Namely, the mean value of the coefficient of internal damping as well as its standard deviation and mean frequency of temporal variations may be estimated directly from the trace of whirl radius which exhibits spontaneous random outbreaks in response.