(5) the air was then turned on for a period of 5 

 minutes; 



(6) temperature, pressure, and flow readings were 

 recorded at the start and finish of the 5-minute period; 



(7) the air was turned off; 



(8) the wave recorders were allowed to run until 

 the waves were again in a steady-state condition; and 



(9) the wave recorder and the wave generator were 

 turned off. 



(i) Summary of Test Results . Unfortunately, the tests 

 were not extensive enough to furnish data that could be analyzed and 

 then transferred to prototype situations other than those used in the 

 tests. However, the tests used values of the primary variables of con- 

 siderable magnitude and the data reflect (more accurately than small- 

 scale models) the quantity of air required for substantial reductions of 

 incident wave heights (the requirements for pneumatic breakwater tests 

 so that the results can be applied to prototype structures are given by 

 eqs. 6-14a to 6-20). Some important conclusions from these tests are: 



(1) The use of pneumatic breakwaters in limited 

 Transportation Corps problem areas is feasible, although the 

 air requirements are rather high; 



(2) the tests (nearly full scale insofar as the 

 offshore discharge problems of the Transportation Corps are 

 concerned) indicate that about one-sixth less air horsepower 

 is required than was predicted by the results of previous 

 small-scale tests, transferred to prototype values based on 

 the Froude law scaling relations; 



(3) wave attenuation by pneumatic breakwaters is 

 primarily a fianction of the wave dimensions, water depth, mani- 

 fold submergence, and the quantity of air discharged by the 

 manifold system; and 



(4) the major part of the attenuation was the 

 result of the horizontal surface currents (generated by the air 

 bubbles) opposing the incident waves. 



(7) Hydraulic Breakwaters . 



(a) Project. Experimental and analytical studies in the 

 mechanics of selected methods of wave absorption. 



(b) Reference . Herbich, Ziegler, and Bowers (1956). 



439 



