T.M. No. 72 - March 1955 



Laboratory Study of the Generation of Wind Waves in Shal low Water 

 by Osva Id J . Sibu I 



Wave generation in shallow water was studied in a small enclosed 

 wind-wave tank in the laboratory for both smooth and rough bottom 

 conditions. The data indicate Sverdrup-Munk-Bretschneider curves 

 may be used to predict wave height and period for relatively deep 

 water, but in shallow water (d/Ho less than 5) the depth starts to 

 affect the wave height, resulting in heights considerably less than 

 predicted. Wave periods are also affected by depth but to a lesser 

 degree than wave heights, the reduction being noticed when d/Lo is 

 less than 0.2. 



T.M. No. 75 - Apri I 1955 



Graphical Approach to the Forecasting of Waves in Moving Fetches 

 by Basi I W. Wi I son 



Development and application of a graphical technique to the 

 determination of maximum significant wave heights and periods 

 attained by waves in moving wind systems are described. Existing 

 Sverdrup-Munk-Bretschneider deepwater forecasting data are assembled 

 in a single chart over which a space-time wind-field representing 

 any given moving wind system (in relation to a particular point on 

 the coast) can be placed by superposition for the evaluation of the 

 characteristics of the waves generated at any specific point in 

 space and time within the windfield. The method is applicable to 

 both approaching and receding storms and permits considering decay 

 aspects in the usual way. An application of the method is given 

 for forecasting wave conditions in the path of a hurricane. 



T.M. No. 74 - May 1955 



Water Surface Roughness and Wind Shear Stress in a Laboratory Wave 

 Channel by Osva Id J. Sibu I 



Vertical wind velocity profiles were measured in a laboratory 

 wave channel by use of a Pitot tube, simultaneously with observation 

 of wave heights, periods and water surface slopes. The vfelocity 

 profiles were analyzed for resistance coefficient, characteristic 

 roughness length, and shear stress exerted by the wind on the water 

 surface. Methods for extending the data to field conditions are 

 given. The laboratory results compare favorably with field measure- 

 ments. It is concluded that small-scale laboratory equipment can be 

 used to study mechanics of energy transfer between wind and water. 



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