Davis and Zarnick 



Fig. 20 - Heave /pitch ratio for 

 Model 4889 at zero speed in 

 head waves; transient test com- 

 pared with regular wave test 

 results 



Frequency in cycles per second 



The ahead speed results are presented in Figs. 22, 23, 24, and 25 where 

 again good correlation is noted. 



The appearance of transient wave records taken during this series is some- 

 what different from that of earlier test records. Figure 26 shows the zero- 

 speed test with a wave height record which appears to be distorted in contrast 

 with the smooth quasi- sinusoidal wave behavior presented earlier in Fig. 12. 

 This is a result of one of the techniques which was used to vary the transform 

 amplitude of the input voltage to the wavemakers, a varying frequency sweep 

 rate which caused a nonuniform deformation of the wave shape. 



The progressive transformation of this wave shape is shown in Fig. 27, 

 which presents measurements taken on the program at three locations. For 

 contrast, similar measurements for the transient of the second series of tests 

 are given in Fig. 28, where the contraction of the shape is much more orderly. 

 In both figures, waves were measured without a model in the water. 



Another interesting test performed during this series employed a human 

 transient generator. To investigate the degree of corruption of wave height re- 

 cording by model- generated waves, the model was made to oscillate in pitch by 

 manually forcing the bow over a range of frequencies. Generated waves were 

 measured by the two forward wave probes and analyzed for their Fourier con- 

 tent, along with the motion record. The transfer functions, wave height/pitch 

 motion, are given in Fig. 29, where for the nearer probe an average wave height 

 of 1 in. results for a pitch motion of 5 deg over the high-frequency band. The 

 effect of heave is neglected. 



528 



