Hsu and Yu 



nI 10"" 



200 RPM 



I.I cpt wav« 



No wov* 



10 12 



Fig. 1. Influence of 1.1-cps wave on 200-rpm ripple 

 spectra 



% 



1 cps and 1.3 cps waves at 300 rpm is given in Figs. 2 to 5, A close 

 examination of these figures (wave motion is toward the left and the 

 usual Sanborn attenuation scales are marked) reveals that the posi- 

 tions assumed by the ripples influence the mean wave profile. For 

 example, ripple superposition in the 1.0 cps wave caused the mean 

 wave crest to become flattened. However, ripple superposition on 

 the 1.3 cps wave did not cause mean wave profile distortion. Many 

 of the records show ripples superposed in such a way that the crest 

 was sharplv peaked. The existence of such conditions may enhance 

 separation of the air flow over the wave surface. 



A source of error arises from the fact that mean wave pro- 

 files were distorted, and yet their energy was compared with that of 

 Miles' pure sinusoids. An expression consisting of a cosine and sine 

 plus their two higher harmonics was least- squre fitted to each of the 

 mean wave profiles (see below). Results indicated that the total 



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