W -13.5^ 



1.5 



17* 



3" 



i AIR i 



[_CHA_M_BERJ 



WATER 

 CHAMBER 



VERTICAL 

 WALL 



PERFORATED 

 WALLS 



WATER 

 CHAMBER 



as' 



-0.5' -I K0.5" -J i— 0.5" 



MOOEL : PROTOTYPE 

 1 12 



PROTOTYPE X- 13.5 Ft 



Figure 204. Twin water chamber and pontoon floating 

 breakwater for reservoir applications 

 (after Chen and Wiegel, 1969). 



of the structure is 3.5 feet. The vertical back wall extends 8.5 feet down- 

 ward to provide a large moment of inertia of added mass. The air chamber 

 (pontoon) has a cross section of 5 by 6 feet, and can serve as a walkway along 

 the breakwater. The width of the breakwater is 13.5 feet prototype dimension. 



The wave transmission coefficient, CL , as a function of relative break- 

 water width, L/W, is shown in Figure 205. For wavelengths up to about 40 

 feet, the results appear to be reasonably satisfactory. Beyond 40 feet, the 

 curve of transmission coefficient versus wavelength steepens rapidly. The 

 energy dissipation that was expected to occur with this arrangement apparently 

 did not develop. Only a small percentage of the wave energy was dissipated by 

 flow through the perforated walls. The remainder of the energy was either 

 reflected or transmitted into the lee side either through the motion of the 

 structure, which acted as a wave generator, or by wave energy passing under 

 the breakwater. 



4. Fixed-Dissipator Floating Breakwater . 



Chen and Wiegel (1969) evaluated a type of floating breakwater conceived 

 by the California Department of Harbors and Watercraft. The system consisted 

 of a platform 32 feet wide which was ballasted enough to be immersed with the 

 bottom 6 feet below the water surface. A series of gates were suspended 

 upward by their own buoyancy which prevented the platform from sinking. The 

 gates, which had a cross section of 6 by 4 feet, were connected to the plat- 

 form by a 1-foot-wide rubber sheet which acted as a hinge. The gates were 

 designed so that alternate rows of gates would move in opposite directions at 

 any specific time. The restrained motion of the gates was expected to inter- 

 rupt the orbital motion of the waves, resulting in energy dissipation. The 

 experimental results were unsatisfactory because the joint between the gates 

 and the platform was not a simple hinge, and because of the flexibility 



262 



