breakwater part of the protective structures was proposed because of poor 

 foundation conditions and the relatively large tidal range. The floating 

 breakwater would consist of rectangular wooden modules fastened together 

 to obtain the required breakwater length. Each module would be 42.5 feet 

 long, 10 feet wide, and 7.2 feet deep and consist of a wooden framework 

 covered with wood decking on the top and sides, concrete beams for bal- 

 last, and polystyrene for flotation (Fig. 6-51). The mooring systems 

 would consist of either chains fastened to concrete anchors (both sea- 

 ward and shoreward of the breakwater) or piles placed between the break- 

 water modules. The preliminary design of the floating breakwater was 

 based on available wave transmission and reflection data for restrained 

 floating structures. However, actual wave attenuation, mooring forces, 

 and response characteristics of floating structures vary with the shape, 

 dimensions and specific weights of the modules, wave characteristics, 

 water depths, and the mass moments of inertia of the modules. Thus, data 

 to determine the effectiveness of the structures and the magnitude of the 

 forces in the mooring lines were desired. 



(f) Purpose of Model Study . The model study was conducted 

 to determine (1) the effectiveness of the proposed floating breakwater in 

 preventing the transmission of wave heights larger than the acceptable 

 value, (2) the mooring forces for both chain and pile mooring systems, 

 (3) whether resonant oscillations of the proposed structure would in- 

 crease mooring forces appreciably, and (4) the natural period of oscil- 

 lation of the proposed module unrestrained in still water. 



(g) The Model . One module of the proposed floating break- 

 water was reproduced to a linear scale of 1:10 and installed for testing 

 in a wave flume 119 feet long, 5 feet wide, and 4 feet deep. The scale 

 was determined by the dimensions of the prototype structure, the depths 

 of water at the breakwater site, the capability of the wave generator, 

 and the dimensions of the waves selected for testing. The model was de- 

 signed and operated based on Froude's law. The specific weight of the 

 water (Ym) iri the model was 62.4 pounds per cubic foot and that of sea- 

 water in the prototype was 64 pounds per cubic foot. The specific weights 



of the material (y, ) used in constructing the model module were dif- 



bm m 

 ferent than the weights in the prototype. These variations between model 



and prototype values were considered in the calculations to obtain geo- 

 metric, kinematic, and dynamic similarity between the model and prototype 

 structure, (Yw)in/(Yw)p = (Ybm)m/CYbm)p- Dynamic similarity also required 

 that the model structure accurately reproduce the mass, moments of inertia, 

 radius of gyration, depth of flotation, and general geometric dimensions 

 of the prototype structure. The chain mooring lines on the model, designed 

 from equation (6-llb), were fastened to strain-gage measuring blocks on the 

 floor of the wave flume to determine the forces in the mooring lines. The 

 seaside and harborside measuring blocks were positioned at horizontal dis- 

 tances of 195.5 and 86.0 feet (prototype) from the front and rear edges of 

 the floating structure, respectively. The initial tension in each mooring 

 line was 2,200 and 0.0 pounds (prototype) for tests in water depths of 

 29.5- and 10-foot depths, respectively. The lengths of the seaside and 

 harborside chains were 200 and 90 feet, respectively (Fig. 6-52). The 



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