Testing Ship Models in Transient Waves 

 40, 



-40 



Heove-Wove Height ^ 





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140 



100 



200 



160 



120 



80 



.2 .4 .6 .8 1.0 



Frequency in cycles per second 



Fig. Z5 - Phase angle between pitch-wave 

 height, heave -wave height and pitch-heave 

 at a Froude number of 0. 14; transient test 

 compared with regular wave test results 



The results of this final series of tests show clearly that the transient tech- 

 nique is a usable tool for the investigation of ship response to waves; however, 

 further improvement is possible. When considering (1) the very close agree- 

 ment between transient and regular heave/pitch ratios observed in Figs. 20 and 

 24 and (2) the variation in the other frequency response estimates that is due 

 solely to choice of forward or after wave height probe, an unwavering finger of 

 suspicion points to the measurement of the dynamic wave disturbance. 



Figure 30 compares the wave height transform of the zero- speed transient, 

 with that of the forward speed run properly transferred to the frequency scale 

 of the stationary measurement. The general agreement is quite good, but the 

 difference resulting from measurements made only 8 ft apart on the same 

 wave — with forward and after probes — is puzzling. 



To weigh the possibility of this difference being associated with model- 

 generated waves. Fig. 31 displays the same wave height transform at zero speed 

 compared with that of a similar measurement made under identical conditions 

 except that the model was not in the water. The agreement is not impressive, 



531 



