Table 7. Pneumatic breakwater tests of potential scale 

 effects at a 50-percent wave height attenuation. 



Water depth 

 (ft) 



L/d 



♦ (model- 

 prototype tests) 1 



* (laboratory 

 tests) 2 



0.7 



2.32 



0.206 



0.76 



0.7 



1.73 



0.175 



0.64 



0.8 



1.75 



0.282 



0.64 



16.1 



1.45 



0.067 



0.64 



15.6 



1.51 



0.053 



0.64 



9.5 



1.53 



0.097 



0.64 



10.0 



2.20 



0.215 



0.70 



'Rurihara (1958). 



2 Straub, Bowers, and Tarapore (1959) 









Wid 

 Dep 

 Wat 

 SytT 



r 



1 1 



th of Channel < 2.0 ft 

 th of Water • 1.0 ft 





g\ a 



> 





e Length » 1.78 ft 

 bol Wave Steepness 



% ao2 



] 0.04 





^ 





i 

 c 





O06 

 0.08 









°"t 



^ 



^ ( 



A 



> o 



o 











" n 



a 







0.005 0.010 0.015 0.020 0025 0.030 0.035 



Unit Discharge q of Free Air (ft 3 /s/ft) 



Figure 141. Effect of unit air discharge, q, and incident wave 

 steepness, H^/L^, on effectiveness of pneumatic 

 breakwater (after Straub, Bowers, and Tarapore, 1959). 



(2) Effect of Orifice Area. Straub, Bowers, and Tarapore (1959) 

 tested this effect in the larger channel with orifices of 1/8- , 3/ 16-, and 

 1/4-inch diameters and with L/d values of 1.22, 1.78, and 2.44, respec- 

 tively. These data are shown in Figure 142 which indicates no pronounced 

 change in the air requirements for the different orifice sizes. 



(3) Effect of Multiple Manifolds . Straub, Bowers, and Tarapore 

 (1959) originally hypothesized that a multiple manifold (parallel manifolds 

 spaced a finite distance apart for simultaneous air release) system would be 

 advantageous for attenuation of longer waves. This would provide a deeper 

 (thicker) surface current which would enable the breakwater to intercept the 

 orbital motion over a greater part of the wavelength. It was also believed 

 if the manifolds were sufficiently far apart, they would each attenuate the 

 wave and thus provide extremely high attenuations. Up to four manifolds at 



203 



