Taking a look at Vibration Testing

摘要

Test engineering Joseph (Joe) A. Youngman, our hero, greets an audience of his A-1 Testing Lab coworkers for this fifth and final lecture session. They've asked for a not-too-deep explanation of the somewhat mysterious activities that take place in A-1's "shaker lab." "Good morning. I hope you'll remember that on our first two Mondays, we discussed one-frequency-at-a-time sinusoidal vibration testing. My intent was to prepare you, to help you understand, on Mondays three to five, random vibration testing. Last week, session four, we discussed analog computer control of random vibration testing." Joe begins by saying, "Let's now look at digital controls, where specified values of PSD (or Power Spectral Density) g~2/Hz are maintained simultaneously in several hundred relatively narrow bands across a frequency range perhaps 20-2,000 Hz." (Figure 1.) He continues, "So I'm told, computer control of random vibration tests got to be practical about 1966, with the Cooley-Tukey FFT algorithm. Operations that previously required 106 computations to calculate what was happening at 1,000 frequencies now only needed 104 calculations. But - at that time - to do this required a roomful of computer gear.