fluid pressure for the data set shown in fig1 and 14 fig1 and 16 show a typical spectrogram and the frequency plot for vibration data from a mach 1 motor the spectrogram shows a high amplitude peak at around 10 9 hz followed by smaller peaks at other frequencies this peak shown in fig1 and 16 at 10 9 hz corresponds to the motor whirl frequency n r u03c9 m and the rest of the smaller peaks represent the modulated motor whirl frequency peaks given by n r u03c9 m u00b1 n u03c9 s since the motor whirl frequency is given by the expression u03c9 m n r the measured value of 10 9 hz is used to calculate the motor rotational frequency at 2 18 hz which in turn corresponds to a rotor speed of 131 rpm this correlated with an actual measurement of the rotor speed of 137 rpm the rotor speed was computed using the formula previously provided that rpm u03c9 m 2 u03c0 60 where u03c9 m is the motor frequency in radians per second fig1 is the spectrogram of the pressure data with the related frequency plot being fig1 both of these figures show peaks at multiples of u03c9 s with u03c9 s being the pump stroke frequency there are higher amplitude peaks at 3 6 and 9 times u03c9 s in addition these.