<- 0.2 



0.005 0.010 0.015 0.020 0.025 0.030 



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



0.035 



Figure 144. Effect of unit air discharge, q, and manifold spac- 

 ing on effectiveness of pneumatic breakwater (after 

 Straub, Bowers, and Tarapore, 1959). 



(4) Power Requirement. The horsepower required for a potential pro- 

 totype installation was computed, based on the results of the small-scale 

 laboratory experiments of Straub, Bowers, and Tarapore (1959). Since it was 

 previously determined that attenuation was effectively independent of wave 

 height, the steepness was not a pertinent parameter for the pneumatic break- 

 water. For an installation depth of 40 feet and for various wavelengths 

 (periods), the attenuation as a function of applied horsepower per foot of 

 breakwater is shown in Figure 145. Because of the possible scale effects 

 involved with extrapolating small-scale data with parameters that cannot be 

 properly scaled in the model, additional larger scale laboratory tests were 

 performed with prototype-size wave heights. Field installations were required 

 to input power of sufficient magnitude to overcome any supply pipeline losses, 

 as well as provide a release rate of air for the desired attenuation. Accord- 

 ingly, for an applied 100 horsepower per foot, the total power requirement 

 including losses for various supply-line diameters was determined (Straub, 

 Bowers, and Tarapore, 1959). The total applied power depends on the length of 

 both the breakwater and the supply lines. The data in Figure 146 assumes that 

 the supply line is 250 feet long with a total coefficient of 1.00 for losses 

 of valves and bends. From this direct extrapolation of small-scale experi- 

 mental data to prototype scale, the total horsepower requirement appears 

 excessive, except for very limited specific applications. Carr (1950) pre- 

 viously concluded that, for typical ocean waves with 10-second periods or 

 greater in nearshore waters, the pneumatic breakwater system did not appear to 

 be a viable alternative. However, for the attenuation of deepwater waves of 

 finite areal extent, the pneumatic system may be worthy of evaluation. 



Colonell, Carver, and Lacouture (1974) conducted an experimental study of 

 pneumatic breakwaters to examine the efficiency of the system in a wind- 

 generated wave environment, although the verification of Kurihara's (1958) 

 eddy viscosity theory was beyond the scope of the investigation. As the 

 breakwater power input was increased, greater degrees of randomness of the 



205 



