Ratio of Wavelength-to-Structure Width, 



Figure 173. Effect of relative breakwater width, L/W, and bag length on 

 wave height attenuation of water-filled, bag-type floating 

 breakwater (after Ripken, 1960b). 



damping caused by the pressure constraint provided by the bag walls in inter- 

 fering with the orbiting characteristics of the bag content. Preliminary 

 tests indicated that the scale effects would probably not exceed 10 percent 

 if these data were extrapolated to prototype conditions. Jones (1974) also 

 reanalyzed the data of Ripken (1960b) and Frederiksen (1971) for comparison 

 purposes, since different configurations of bag types and wave characteristics 

 had been used (see Figs. 174 and 175). 



(2) Mooring Force Evaluation . The peak force required to stabilize 

 the actively oscillating, floating fluid-filled bag breakwater was inherently 

 related to the mass characteristics of the structure, the motion character- 

 istics of the structure in a given wave climate, and the degree of constraint 

 imposed by the mooring system. Since the mass and motion characteristics of 

 the structure and waves were presumably simulated in the model studies, deter- 

 mining the representative model forces would depend on selecting a mooring 

 system having suitable constraint. Preliminary small-scale tests indicated 

 that the peak mooring force increased by about 30 percent when the line was 

 changed from moderate elasticity to low elasticity. Ripken (1960b) conducted 

 subsequent tests with moorings of low elasticity, thus obtaining relatively 

 large or conservative peak mooring forces. For tests in the 6- and 24-inch 

 channels, the mooring line consisted of a solid strand of stainless steel 

 music wire (0.01-inch diameter). For tests in the 9-foot channel, the line 

 was a 1/16-inch stainless steel aircraft cable of 7 by 7 stranding. The 

 mooring force data (Fig. 176) were determined with a mooring line slope of 

 1:10. Pilot tests with slopes varying from 1:4 to 1:10 indicated that line 

 slope variations in this range had little influence on the peak force values. 



233 



