TM No. 377 



somewhat smaller than those estimated by Francis et al (1953). These studies, 

 although somewhat inconclusive in their preliminary analysis, indicate that 

 properly conducted Eulerian measurements of particle velocities in the water 

 column can be used to estimate the statistical turbulent properties inherent 



in the motions of the water. 



Stewart and Grant (19&2) obtained near-surface measurements of high wave 



number, turbulent, velocity fluctuations (in one dimension) by towing a 

 horizontal, hot film, anemometer-like device from a vessel while underway. 

 The authors infer values of turbulent energy in its last stages of decay 

 prior to frictional dissipation. The validity of the one dimensionial 

 measurement is based on the Kolmogoroff concept (Kolmogoroff, 19^1 ) that 

 fine structure turbulence tends to be isotropic. According to the authors, 

 most of the energy acquired by the waves from the wind is quickly converted 

 into isotropic turbulence within a depth commensurate with the wave height. 

 If this is true, the value of the Reynolds stress should decrease sharply 

 as one moves to a depth beyond one or two wave heights. These experiments, 

 however, shed no light on the problem of what happens to the wind- imparted 

 momentum from the time it is anisotropically transferred to the water 

 surface until it is dissipated as fine structure isotropic turbulence. 



One other system of interest is under development at the Chesapeake 

 Bay Institute (of Johns Hopkins University). In this system the doppler 

 shift of acoustic energy scattered from a small volume of water is used 

 to infer the instantaneous particle velocities. The system, according to 

 Pritchard (1964), is 'designed to supply a three-dimensional picture of the 

 instantaneous motions in a volume of the order of a few cubic centimeters. 

 Although certain technical problems -will have to be overcome, this concept 

 has promise because there is no apparent interference with the flow within 

 the volume of water under examination. 



Laboratory Experiments «== Three laboratory studies of particle motions 

 are worthy of mention. Shuliykin (1959) reports on Lagrangian particle 

 measurements in waves produced in a ring-shaped "storm basin*' in the Marine 

 Hydrophyaical Institute, .Moscow. Small, neutrally bouyant, spherical lamps 

 were photographed as they oscillated beneath the surface of waves generated 

 by an artificial wind in the basin. 



The motion picture films, display the orbital motions, with a quasi- 

 circular component of the actual orbit superimposed upon a translational 

 motion. The resulting lagrangian orbit resembles a prolate cycloid, i.e., 

 the locus of points generated at the end of a line segment extending from 

 a radius of a circle which is rolling on a horizontal plan® (see Larson, 

 1956). The slight elongation of the orbits is attributed to the shoal 

 conditions in the tank. The relationship between these Lagrangian patterns 

 and those which occur in natural waves is very tenuous, since no effort was 

 made to assess the effects of the artificial generation and, even more 

 important, the effects of the horizontal boundaries of the storm basin. 



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