Figure 162 showed excellent wave height attenuation for small values of the 

 ratio of wavelength-to-trap length. The attenuation coefficients then dimin- 

 ished with increasing values of the ratio; reflection was not a major factor. 

 The Wave Trap showed a slight decrease in performance with increased wave 

 steepness. Limited duration tests indicated the system design appeared to be 

 restricted to wave heights of about 1 foot. Larger values produced evidence 

 of structural damage due to the dynamic wave forces. Direct scaling to proto- 

 type dimensions for ocean-type installations would involve wave heights 5 to 

 10 times those of the laboratory tests; hence, the internal forces and stres- 

 ses would range from about 100 to 1,000 times as great as those in the model. 

 It appears impractical to design a Wave Trap to sustain such prototype forces. 

 Ripken (1960a) recommended that the sheet spacing be retained at a distance 

 that would provide a differential vertical orbiting distance of about 1 foot. 





■ 















■ 



• 



O 



• 









Trop Deplh = 3 3 ft 

 Trap Length = 20 ft 















Mooring Line Slope = I : I0 







■ 









Tests No. 167-176, 191-201 











k 















* 



c 

 c 



> 









Wove 

 Steepnes 



Symb 

 5 Original 



Condition 



1 



With 



Revision 





1 



1 





A. 



8 

 A 





0.02 



0.03 



0.04 

 006 

 008 

 0-10 



o 



A 



a 



• 

 A 

 ■ 



Q 















a. 



« 















O 0.2 0.4 06 0.8 1.0 1.2 1.4 1.6 I 



Ratio of Wavelength-to-Structure Width, L/W 



Figure 162. Effect of relative breakwater width, L/W, and incident wave 

 steepness, H^/L^, on wave height attenuation for the Wave Trap 

 membrane-type floating breakwater concept by U.S. Rubber Company 

 (after Ripken, 1960a). 



(2) Mooring Force Evaluation . Ripken (1960a) conducted tests with 

 the Wave Trap structure moored by a single cable running at a selected slope 

 angle between the mooring tube lashed to the front of each absorber and a 

 mooring line anchor on the channel floor. The mooring forces were evaluated 

 with a dynamometer which measured the tension in the mooring cable at the bot- 

 tom anchorage. The mooring line force data obtained from these rather limited 

 tests are shown in Figure 163; the data were obtained under two-dimensional 

 conditions and should be used conservatively. In low steepness waves, the 

 Wave Trap tends to move forward into the oncoming wave train. This situation 

 requires either stern mooring lines or revision of the check valves to provide 

 a better balance of valve-induced horizontal forces. 



222 



