4. General Operational Aspects . 



Certain fundamental operational aspects exist which are common to all 

 types of floating breakwaters. These include the determination of the incip- 

 ient wave conditions for performance considerations, and the type of anchoring 

 system to be developed for a particular location. The basic methods by which 

 a floating breakwater reduces wave energy to produce a sheltered region 

 include: (a) reflection, (b) dissipation, (c) interference, and (d) conver- 

 sion of the energy into nonoscillatory motion. For effective reflection, the 

 breakwater should remain relatively motionless and penetrate to a depth suf- 

 ficient to prohibit appreciable wave energy from passing underneath. The 

 structure could extend to the bottom and obstruct most of the water column, 

 but it usually floats with a draft much less than the water depth. For short 

 waves in the upper part of the water, deep draft is not needed; for long 

 waves, deep draft may be desirable but again it is difficult to contend with 

 the large mooring loads which may result. Optimization is often required 

 between the wave attenuation aspects and mooring loading. Because of this 

 turbulent dissipation of energy, forces in the mooring system are accordingly 

 reduced. 



a. Performance Considerations . The generally accepted criterion for 

 evaluating a breakwater's performance is the transmission coefficient, C . 

 This parameter is usually defined as the ratio of the transmitted wave height, 

 tL, to the incident wave height, H- 



H, 



(1) 



This definition is satisfactory as long as the waves are regular; however, in 

 wave climates consisting of short-crested irregular waves, the definition may 

 need to reflect the amount of energy transmission instead of wave height 

 transmission. Accordingly, a transmission coefficient is frequently formu- 

 lated as the ratio of the transmitted wave height squared, H?, to the inci- 

 dent wave height squared, H? 



H? 



(2) 



As with all breakwaters, the design of a floating breakwater is always 

 site-specific. Waves favorably attenuated by a floating breakwater usually 

 do not exceed 4 feet in height, and periods usually do not exceed 4 seconds. 

 Hence, for these relatively short-period waves, refraction and diffraction 

 probably do not enter into the determination of the wave climate. If neces- 

 sary, however, these effects can readily be incorporated into the design 

 considerations. The wavelength, L, is uniquely related to wave period for 

 the water depth in which the wave is propagating as 



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