(1) Effect of Relative Wavelength . Experimental data were obtained 

 for values of relative wavelength, L/d, up to 5.60. It appeared that the 

 dimensionless horsepower ratio, $, remained fairly constant for values 

 of L/d up to about 2.00, and then increased rapidly for larger values of 

 L/d. Figure 151 illustrates typical data for a 100-percent attenuation; the 

 power requirements for a single manifold increased by a factor of 7 as 

 the L/d value increased from 2.00 to 5.00. 



12 





Attenuation 



00% 







10 





Jot Diameter Symbol 









0-166 



o 











0O923 



a 







*o 













8 

























.9 

 o 



or 



Q- 











/ ° 





c 

 o 



c 4 



1 



b 











/ 















2 



0-* 





















°( 



o 











) 





> 



s « 





5 6 



Ratio of Wavelength-to-Water Depth, L/d 



Figure 151. Effect of relative wavelength, L/d, and 

 nozzle jet diameter on horsepower require- 

 ments, $, of hydraulic breakwater (after 

 Herbich, Ziegler, and Bowers, 1956). 



(2) Effect of Wave Steepness . Wave steepness was found to have an 

 important effect on power requirements, unlike the performance of the pneu- 

 matic breakwater. Figure 152, which presents typical data for three L/d 

 ratios, displays the effect of wave steepness, H./L. , on the dimensionless 

 horsepower ratio, $. Considering the curve of L/d = 3.33, an increase in 

 wave steepness from 0.02 to 0.08 (a factor of 4) increased the required 

 horsepower ratio by a factor of about 3. The true efficiency, e (ratio of 

 attenuated wave energy-to- jet energy), however, was considerably higher for 

 the steep waves than it was for the lower waves. 



(3) Effect of Jet Area. Herbich, Ziegler, and Bowers (1956) found 

 one of the most important parameters affecting both the dimensionless dis- 

 charge, Q, and horsepower ratio, $, to be the jet nozzle cross-sectional 

 area per linear foot of breakwater. This jet area is dependent on the jet 

 spacing and the jet size, both of which were varied over considerable ranges 

 during the test program. A dimensionless jet area was defined as the ratio of 

 the area of the jets to the cross-sectional area of the wave channel; the 

 ratio was correlated with the dimensionless discharge and horsepower ratios 

 (Fig. 153). These data indicate that the discharge and power requirements are 

 strongly dependent on the jet area. The power requirements decrease as the 



212 



