Savitsky 



is increased to 1 . 7 ft/sec. These results are to be compared with 

 those on Figs. 6 and 8 for a grid speed of 1 . ft/sec. The major 

 differences are that there are wider variations in wave amplitude at 

 the higher grid speed and, further, the periodicity of the phase rela- 

 tion is reduced from 60 seconds to 40 seconds for the 3 ft wave and 

 from 85 seconds to 50 seconds for the 4 ft wave. Unfortunately, 

 sufficient data were not collected to determine the effect of grid 

 velocity on apparent wave length. Similar data exist for the longer 

 test wave lengths but, for the sake of brevity, these are not included 

 in the present thesis. 



Effect of Grid Mesh Size : Increasing the grid mesh size from 

 2.7" to 5.4" did not have a discernible effect upon the test results, 



Two-Dimensional Grid Studies 



The objective of these two-dimensional studies was to investi- 

 gate the interaction between a turbulent flow field of finite dimensions 

 and long-crested, deep water, gravity waves. As previously dis- 

 cussed, the grid wake characteristics were such that the waves were 

 simultaneously subjected to dissipation effects due to eddy viscosity; 

 scattering due to turbulent convective distortion of the wave front; 

 and deformation of the wave due to mean flow velocity gradients. As 

 in the one -dimensional investigations, it appears that the effect of 

 the velocity gradients dominated in developing major wave distortions. 

 Although the experimental program examined wide variations in wave 

 length, wave height, grid mesh, grid width, grid draft, and grid 

 speed, the presentation will be limited to a discussion of results for 

 the following brief range of conditions: 



X = 2.0; 6,0 ft 



H^= 1.0 inches 



Grid mesh =2.7 inches 



Grid draft = 0.83; 1.67 ft 



Grid width = 3.0 ft 



Grid velocity = 1.0, 1.6, 2.6 ft/sec 



These limited combinations of parameters serve to illustrate the 

 major effects of wake -wave inte ration. 



General Behavior: The behavior of the time history of the 

 wave amplitudes at probe positions, either moving with the grid or 

 stationary In the wake, were substantially different from the one- 

 dimensional results previously discussed. The extensive Irregularity 

 In the wave anmplltude were not observed -- particularly for those 

 wave probes which traveled with the grid. There did appear to be 

 some Indication of an irregularity for those stationary wave probes 

 located approximately two grid widths from centerllne -- these were 

 not, however, well defined. An examination of the crest line defor- 

 mation as a given wave passed over the transverse line of stationary 



412 



