Experimental study of the critical speed response,of a jeffcott rotor with acceleration

A small, lightly damped rotor (ζ=0.0088) was experimentally tested for a variety of acceleration and deceleration rates. In each case, the amplitude response was plotted as a function of operating speed, with the acceleration rate considered. In each case the results are compared with theoretical predictions. The results agree within 6% at the peak response. The results of the analysis indicate that for high acceleration rates the critical amplitude response may be reduced by a factor of four or more. The frequency of the effective critical speed may be shifted by up to 20%. Furthermore, a beating frequency was observed in the amplitude data after the rotor had passed through the critical speed. This phenomenon is shown to be the vector sum of a synchronous component of amplitude and a nonsynchronous transient component (at the critical speed). The transient nonsynchronous component is shown explicitly via electronic band-pass filtering, as is the forced response component. Finally, spectral analyses were performed over a range of operating speeds, yielding waterfall diagrams and further verification of the existence of the two components.