Davis and Zarnick 



.2 .4 .6 .8 1.0 



Frequency in cycles per second 



Fig, 14 - Pitch response for Model 4606 

 at zero speed in head waves; transient 

 test compared with regular wave test 

 results 



accuracy. By far the major source of error concerned the measurement of 

 wave height, either through the corruption of the incoming wave with model- 

 generated waves or through some nonlinear mechanism associated with water 

 dynamics or wave measurement. 



Several further improvements in test technique appeared feasible as a re- 

 sult of this second series. First, the use of an excitation voltage with varying 

 frequency and constant amplitude resulted in a water wave having essentially 

 the same frequency but an amplitude which reflected the sensitivity of the wave- 

 making system to certain frequencies. This type of excitation influences the 

 magnitude of the wave height transform; see Fig. 15 which shows these large 

 variations over the frequency range. It was felt that preliminary amplitude 

 weighting of the control voltage would counteract the known frequency character- 

 istics of the basin and produce a wave with more uniform distribution of energy 

 over the frequency interval used in testing. The result would be that (1) extra- 

 neous "noise" in wave measurement would be overridden by significant amplitude 



524 



