Upon spectral analysis, the white noise signal which had been used to excite the 

 analog computer circuitry displayed a disconcerting but predictable lack of smoothness, as 

 shown in Figure 11. This irregularity was present to some extent in every excitation and 

 wave spectrum observed throughout this wave testing, and it greatly complicated program 

 correction analysis. 



Two sets of frequency corrections were made, using the analog computer to synthe- 

 size correction networks. The final spectra developed in this exploratory program are shown 

 in Figures 5, 6, and 12. These corrections were not uniformly successful indicating that 

 at least mild nonlinearities in wavemaking were present, that the analog spectral analysis 

 equipment was deficient in performance, or that the spectra depended to some extent on 

 where in the basin the wave heights were measured. 



To investigate some of these possibilities, a series of wave measurements was made 

 in January 1963 with variation in program running level (attenuation of the tape recorder 

 signal), blower speed, and basin location. These resulting spectra are displayed in Figures 

 13, 14, and 15 where a severe variation in spectral shape occurs as a function of location, 

 but only a mild variation develops for changes in the wave-height level. The controlling 

 program, which was repeated during each wave measurement, was designed to have essen- 

 tially constant energy content over the frequency range of interest and thus to have the 

 shape of each spectrum proportional to the square of the frequency response of the wave- 

 making system. 



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FREQUENCY IN CPS 



Figure 11 — Spectral Analysis of Signal from White Noise Generator 

 with 30-Minute Recording Time 



14 



