PLAN VIEW 



FREEBOARD 



-MOORING LINE ^-BALLAST 



SECTION A-A 



Figure 114. Definitive sketch of a tethered-f loat breakwater. 



The natural frequency of oscillation of the tethered float is inversely 

 proportional to the square root of the tether length, as in the case of a 

 pendulum. The tethered float responds to the periodic wave-driving force with 

 a definite phase relationship. The responses are typical of damped oscil- 

 lators (Fig. 6), with the float motion amplitude peaking near the natural 

 frequency, and with the phase lag angle increasing with increasing wave 

 frequency. In effect, the floats can have a natural frequency approximately 

 equal to the incident wave frequency. Near resonance, the float motion is 

 greatly amplified and out of phase with the fluid particle motion. If there 

 are wave components with frequencies near the natural frequency of the floats, 

 the relative velocity will be quite high because the floats are moving a 

 greater distance than the local water particles, and because they lag the 

 water motion substantially in their phases. Because of their dynamic 

 response, it is possible to cause the buoys to pendulate in the incoming wave 

 field out of phase with the wave orbital motions. The effect of this wave- 

 excited buoy motion is to transform wave energy into water turbulence and then 

 into heat into the wake of the buoy. 



2. Performance Estimation . 



Because preliminary laboratory measurements of the tethered-f loat break- 

 water suggested that scattering and reflection are minor contributors to the 

 reduction of wave energy, the analytical model for predicting the performance 



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