Savitsky 



resulting in "splash turbulence" penetrating Into the upper layers of 

 the water; turbulent fields set up in intense currents; turbulence 

 developed by high velocity, high Reynolds number flows in a tidal 

 channel; ship wakes; etc. In each case, it Is expected that wave 

 attenuation will result from the interaction between the turbulent flow 

 fields and wave motion. Such attenuation is of importance in develop- 

 ing relatively "quiet" local areas in the sea for launching or recovery 

 of small craft or submarines, or in tracing the progress of, say, 

 one storm passing through the intensive turbulence of another storm, 



Phillips [ 1959] presents a theoretical study of the properties 

 of waves on the free surface of a liquid in turbulent motion where the 

 intensity of the turbulence is sufficiently small to preclude wave 

 generation In itself and where the mean velocity of the flow is zero. 

 There are two types of possible interaction, each of which results In 

 the attenuation of the incident wave. One Is an "eddy viscosity inter- 

 action" in which wave energy is transferred from the wave motion 

 through a stretching of the vortex filaments in the turbulence which 

 tends to Increase to^, the mean square vortlcity associated with the 

 turbulence itself. This straining process is of second order in wave 

 height-length ratio and, hence, should be Important for steep waves 

 and when the turbulence scale is much less than that of the waves. 

 The second type of interaction is a scattering phenomenon where 

 random velocity fluctuations In the turbulence field will result in the 

 convective distortion of the wave front, and produce a broad spectrum 

 of scattered waves. This scattering effect is of first order in wave 

 height-length ratio and, hence, predominates for waves of small 

 slope. Phillips shows that, under typical conditions In the open sea, 

 the attenuation from scattering will be greater than that from direct 

 viscous dissipation for wave lengths greater than about 10 ft. 



An experimental study was undertaken at the Davidson Labora- 

 tory, Stevens Institute of Technology, to investigate the Interaction 

 between mechanically generated progressive gravity waves and a 

 controlled turbulence field developed by towing suitable grids in a 

 towing tank. Since field measurements by Stewart and Grant [ 1962] 

 supported the applicability of the Kolmogoroff hypothesis (that the 

 statistical structure of turbulence has a universal form) to turbulence 

 near the sea surface In the presence of waves, it was believed that 

 grid-generated turbulence (known to satisfy the Kolmogoroff hypothesis) 

 would indeed be representative of ocean turbulence on a model scale. 

 Two experimental studies were undertaken. The first used a grid 

 which spanned the width of a 1 2 ft wide towing tank and was towed In 

 the direction of wave celerity at speeds less than the group velocity 

 of the regular wave lengths generated by a plunger type wavemaker. 

 In these studies, the test waves overtook and passed through the 

 turbulence wake and grid. This so-called one-dlmenslonal grid study 

 was made in an attempt to develop a turbulent wake with uniform 

 mean flow across any transverse section aft of the grid. Unfortunately, 

 as win be subsequently discussed, a uniform flow field was not de- 

 veloped near the outer edges of the grid wake and this seriously 



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