A study of asynchronously excited oscillations in nonlinear control systems

This study was initiated as an effort to explain certain oscillatory phenomena observed in an aircraft and weapon control system operated in a particular mode. The oscillations in question were of the undamped limit-cycle type and their presence could very clearly be correlated with the degree of noise corruption of the signals. It is demonstrated in this paper that certain types of nonlinear systems although being inherently stable may be driven into oscillatory modes not only by random signals but also by any high frequency periodic or nonperiodic signal possessing a certain energy content. It is of interest to note that the tendency for hunting and also the hunt frequency usually are completely independent of the frequency of the excitation signal, i.e., the phenomenon is of asynchronous nature. A general theory, the validity of which has been tested by both analog and digital means, is presented and utilized to demonstrate how this phenomenon may be predicted from information on circuit data.