installation in the experimental facility for attenuation and mooring load 

 determinations. 



An important requirement of hydraulic model testing is the establishment 

 of the modeling laws regarding basic forces which dominate the physical proc- 

 esses. For model tests of many hydraulic designs, previous experience has 

 defined the dominant force system and the related model laws of similitude. 

 However, there is no precedent for the Wave Blanket which clearly establishes 

 the force mechanism. An analysis of the force system, which dominates the 

 fluid dynamics of the blanket action, indicates that both viscous and gravity 

 forces may be involved extensively. It was originally hypothesized that vis- 

 cous action in the permeable blanket structure controlled the attenuation 

 effects, but the extent to which gravity effects are felt is obscure. Because 

 of the variety of factors which interact in the Wave Blanket system and the 

 inability to scale the physical properties of the system, it is difficult to 

 summarize the performance. 



(1) Wave Attenuation Effectiveness . Since various thicknesses (lay- 

 ers) of the Wave Blanket were tested, Ripken (1960a) treated the test data as 

 broad, inclusive bands representing significant differences in thickness. 

 Figure 166 indicates that the degree of attenuation increased as the ratio of 

 wavelength-to-blanket width decreased, and as the ratio of blanket thickness- 

 to-water depth increased. For a thin blanket, the width should be several 

 times the wavelength, and the thickness should be about 15 percent or more of 

 the water depth. A blanket construction with decreasing thickness from front 

 to rear has approximately the same attenuation characteristics as a blanket 

 with the same width and volume and a uniform thickness. A blanket fabrica- 

 tion, using a dense sponge, gave essentially the same type of attenuation as 

 the blanket of permeable Trilok. The conclusion was that internal flow 

 resistance within the Trilok material accounts for only a minor part of the 

 total energy dissipation. Attenuation did not appear to be critically depend- 

 ent on the structure of the blanket, provided the system interfered with 

 orbiting of the contained fluid. 





"""'"""III.,, 







!")«J,„. A 









= 8 In. Thick Blanket, t/d- 0/54 

 16 la Thick Blanker, t/d> 16/54 

 m 24ln. TMck Blanket. t/d> 24/54 

 O Original Win Trap. Tnli 167-176 











i 



L 



p 5 ^ 



•"'", 



;1 ^fi!^ 











-~f: ; ; c 















i 



hhhjIII 



!t|%"I2,;ip§jn 



-5=—:^ 











m e '.=: :■■ 



=—=—.-■■:.:— 



























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

 Figure 166. Effect of relative breakwater width, L/W, and various thick- 

 nesses and widths of blanket on wave height attenuation by Wave 

 Blanket concept of membrane-type floating breakwater of U.S. 

 Rubber Company (after Ripken, 1960a). 



225 



