Testing Ship Models in Transient Waves 



.2 .4 .6 .8 



Frequency in cycles per se 





 cond 



Fig. 8 - Pitch response for Model 4941 

 at zero speed in head waves; transient 

 test compared with regular wave test 

 results 



tests. The only severe deviation is a sharp peak near 0.35 cps in both responses; 

 it was caused by an unexplained sharp null in the measured wave height trans- 

 form. 



In Fig. 9 the heave/pitch ratio is plotted for the zero-speed case. Although 

 heave/pitch ratio plays no part in prediction of motion, it is a ratio which has 

 as much significance as any other in the isolated transient experiment, since all 

 three dynamic quantities are "effects," as previously discussed. This ratio has 

 the virtue of being independent of errors in wave height measurement, and has 

 provided a useful index of the accuracy of the motion measurements throughout 

 the series of transient tests. 



A forward speed transient test was conducted at a speed corresponding to a 

 Froude number of 0.09. Unfortunately, heave calibration was lost and only pitch 

 results are valid, as given in Fig. 10. These results show a moderate agree- 

 ment with the regular wave pitch response. 



In analyzing the results of these initial tests, it was felt that the transient 

 technique had demonstrated considerable promise but that there were many pos- 

 sibilities for improvement in testing techniques. 



519 



