235 



Fig. 5 Wave Refraction 



While the refraction causes the deep wave to focus toward the center, 

 once the wave breaks due to reduced or shallow depths, refraction principles 

 no longer apply. It is then necessary to have some structure to guide the 

 wave energy through the surf zone (Fig. 6). The inner portion of the guide 

 vanes is contoured so that the energy is introduced tangentially into the core, 

 and thus the fluid flywheel is created. 



A distribution of relative energy content in ocean waves as a function of 

 the deep water wave length or periodicity of the waves is shown in Figure 7. 

 While this distribution is not applicable all over the world, there is a pre- 

 ponderance of wave energy in those waves which have a period or frequency 

 between 5 and 10 seconds. The 10 second period corresponds to wave lengths of 

 156 meters, and the peak of this curve at 7 seconds corresponds to a wave 

 length of 78 meters. 



Examining a 10 second wave pattern which has a crest-to-trough height of 

 two meters. Figure 8, shows an energy content of 4 Mw (or 4000 Kw) of energy 

 per 100 meters of wave front. Or for each meter of wave front, there is 40 Kw 

 (or 40,000 watts). The height of the waves, or swells, is important because 

 the energy content is proportional to the square of the height. 



One of the key features of the DAM-ATOLL system is that its performance Is 

 not dependent upon a directional orientation. Regardless of the approaching 

 wave direction, or for random seas, the wave refraction will occur so that the 

 energy is directed and concentrated to the central part of the special dome 

 shape structure. 



The dome size which concentrates the wave energy needs to be about the 

 same diameter as the predominant deep water wave length, hence the earlier 

 statement that the dome should be in the order of 100 meters in diameter. 



