The primary purpose of the study, hoKever, was to show qualitatively 

 that the pressure gradient developed in laboratory wave-wind flume of 

 constant cross section contributes significantly to wave growth. This 

 result was achieved. 



c. Experiments by Shemdin and Hsu . Shemdin and Hsu (.1966) made a 

 significant contribution to the art of laboratory study of wind-wave 

 generation by introducing a rough transition plate to speed the develop- 

 ment of a turbulent boundary layer above the water surface and thereby 

 achieve a more natural velocity profile. This is essential for modeling 

 the Miles invicid wave-generation process. Shemdin and Hsu used a 

 combination wind tunnel-wave channel with a working section 28 meters 

 (85 feet) long, 1.89 meters (74.5 inches) high, 90.2 centimeters 

 (35.5 inches) wide, with a nominal water depth of 91 centimeters (3 feet). 

 They neglected the constriction of the free stream and the consequent 

 pressure gradient in the downward direction. Shemdin (1969a) extended 

 this verification study of the Miles mechanism and reported that the 

 actual wave growth was generally greater than that predicted by the Miles 

 theory. This result is consistent with Liang's finding that the pressure 

 gradient developed in a laboratory wave -wind flume contributes an addi- 

 tional factor to wave growth not observed in nature. Shemdin used a com- 

 bination wind tunnel-wave channel with a working section 36.6 meters 

 (120 feet) long, 1.93 meters (76 inches) high, including a nominal water 

 depth of 91 centimeters (36 inches). The facility was 86.4 centimeters 

 (34 inches) wide. Although pressure gradients were neglected in this study, 

 Hsu (1965) presented figures showing an acceleration of the core flow in 

 the facility at Stanford University used by Shemdin and Hsu. Shemdin 

 (1969b) reported similar figures for the University of Florida facility 

 used in later studies. The neglect of the pressure gradient in the direct- 

 ion of wave growth casts some doubt about the quantitative validity of 

 many of Shemdin 's results. 



Latif (1974) reported another phenomenon at the University of Florida 

 wind tunnel-wave flume (and presumably in most other research facilities) 

 in which a wind was blown over mechanically generated waves. The wind 

 was led to the water by a ramp which terminated in front of the wave gen- 

 erator slightly above the wave crest. Each mechanically generated wave 

 pushed a slug of air into the wind tunnel forming an acoustic wave in phase 

 with the water wave at the inlet. This pressure wave has the same fre- 

 quency as the mechanically generated wave; however, since the pressure wave 

 traveled at the speed of sound its phase was nearly constant throughout the 

 facility. This pressure wave does not have a counterpart in nature. 

 According to Latif, the amplitude of this acoustic wave was large enough 

 to question the quantitative results of most earlier studies of the relation 

 between atmospheric pressure pulses and wave generation in the laboratory. 

 Since Latif was a student of Shemdin at the time, it may be assumed that 

 Shemdin accepts these findings. However, the qualitative evidence of wave- 

 induced pressure pulses, Reynolds stresses near the water surface, and 

 the effects of surface water waves on atmospheric turbulence is undisputed. 

 The desire to obtain experimental proof of the reality of these predicted 

 effects was among the principle motivations of Shemdin 's studies. 



36 



