Ogilvie 



— 330 



300 U^ 



— < 



— 270 



240 



.0 2.0 



FREQUENCY , fig 



3.0 



Fig. 3 - Dalzell's pitch frequency response function, 

 Model DD 692 Froude number = 0.18 (from Dalzell (1962b)) 



From Fig. 2, it is seen that the f.r. function for F = is practically the 

 same for each wave condition. The statistical design and analysis of the exper- 

 iment will not be considered here; it will sviffice to point out that the confidence 

 to be attached to the f.r. function drops at the ends of the cvurves. No results 

 were presented at all for cases in which either spectral density dropped below 

 a certain value (10% of its peak). 



Figure 3 shows the same results for F =0.18 and Fig. 4 for F = 0.37. In 

 the latter, it is clear that nonlinearities are making themselves felt. In partic- 

 ular, the pitch amplification factor decreases as wave conditions become more 

 severe; this is the trend which one usually expects when nonlinearities become 

 non-negligible. 



14 



