Gravity Waves and Finite Turbulent Flow Fields 



Specific Results : To more clearly Illustrate the modifications 

 in wave height along a given crest line, transverse sections through 

 the wake are plotted in Figs. 19 and 20 for a grid width of 3 ft , draft 

 of 1.67 ft, mesh of 2.7" and speed of 1 ft/sec. The effect of a grid 

 draft of 0.83 is given in Fig. 21. The results for the 2 ft wave are 

 given in Fig. 19 while those for the 6 ft wave are given in Figs. 20 

 and 21. These data are obtained from simultaneous measurements 

 of the recorded wave height at times corresponding to the indicated 

 distances ahead of and behind the grid. A maximum phase shift of 

 only 30° was discernible in the test records. 



It is seen that a substantial reduction in wave amplitude exists 

 for a distance of nearly one grid width on either side of the center- 

 line. The maximum wave height amplification occurs at approxi- 

 mately two grid widths from the centerline and the wave amplitude 

 appears to be unaffected at distances of approximately 4 grid widths 

 from the centerline. This pattern exists for distances well aft of 

 the grid. It is interesting to note that, as the wave passes through 

 and ahead of the grid, where the wake, does not exist, the deformed 

 crest tends to return to its original uniform height. Again, it is 

 seen that the 2 ft wave is much more attenuated and amplified com- 

 pared to the 6 ft wave, all other conditions being equal, (Compare 

 Figs. 19 and 20.) It is also interesting to note that reducing the 

 grid draft from 1 . 67 ft to 0. 83 ft has a negligible effect on wave 

 deformation for the 6 ft wave. (Compare Figs. 20 and 21.) 



1.60 



1.20 



0.80 



0.40 — 



Fig. 19 



4 6 8 



y= DISTANCE NORMAL TO GRID q. -FEET 



Height of wave crest line in transverse sections normal to 

 grid ^, X = 2', H = 1", grid width =3', mesh = 2.7", 



draft = 1.67', V = i ft/sec. 



419 



