Davis and Zarnick 



typical test where the wave transient reached a peak height at the location of the 

 stationary model. Along with these signals, the outputs of the analog computer 

 circuitry (described in the previous section) are displayed for a particular fre- 

 quency of analysis. 



These sinusoidal outputs have magnitudes which are essentially equal to the 

 magnitudes of the Fourier transforms of the respective signals up to that point. 

 Although the variation of these amplitudes at the end of the transient has been a 

 vexing problem with this method of transient analysis, sources of test error 

 have been uncovered such as waves reflected from the sloping beach. 



Another practical difficulty encountered is also seen in the transient wave 

 height record where the energy in the water does not decay rapidly after pas- 

 sage of the main signal. Fortunately, much of this disturbance is above the fre- 

 quency range of interest. 



A zero- speed transient test was analyzed at many different frequencies 

 using the relative lull at the end of the passage of the main wave as the defined 

 end of the transient. Figures 7 and 8 display the resulting heave and pitch fre- 

 quency responses; they show good agreement with those of the regular wave 



Frequency jr. cycles per second 



Fig. 7 - Heave response for Model 

 4941 at zero speed in head waves; 

 transient test compared with regu- 

 lar wave test results 



518 



