Here c u is the undrained cohesive strength of the soil. The pile spacing, 

 as well as the deadweight anchor locations, should be close enough to overcome 

 the peak, lateral forces exerted by the floating breakwater on the mooring 

 lines. 



5. The Study Objective . 



Since the early 1900' s, interest in the applications of floating break- 

 waters has occurred intermittently and to various degrees, and as a result a 

 multitude of conceptual models have been proposed without extensive or com- 

 plete evaluation of most of these concepts. Hence, the technical literature 

 regarding floating breakwater applicability and design procedures is frag- 

 mentary and sometimes confusing. Clear, concise guidance does not always 

 exist for those charged with the responsibility of planning and developing 

 wave protection measures. The 1970's experienced a resurgence of interest in 

 floating breakwaters, and the dearth of design information dictates that a 

 conservative approach be followed when designing both the structure and the 

 anchoring system (which can be significant costwise). Forces on anchors and 

 in structure members should be investigated, in conjunction with the trans- 

 mission characteristics of prototype structures to optimize floating break- 

 water cost and effectiveness. 



This study reviewed and evaluated the technical literature (theoretical, 

 field, and laboratory) on existing floating breakwater concepts. This state- 

 of-the-art evaluation which furnishes a summary of available guidance will 

 also be used in planning further research on floating breakwaters, and will 

 supplement prototype monitoring programs. 



II. THEORETICAL ANALYSIS OF FLOATING BREAKWATER PERFORMANCE 



1. Fixed Rigid Structures . 



The wave attenuation characteristics of floating breakwaters were first 

 investigated from an analytical standpoint by approximations which consisted 

 of idealized forms of wave barriers. A rigid structure of finite width, W, 

 height, h, and draft, D, fixed near the surface of a water body at depth, 

 d (Fig. 1), was analyzed by Macagno (1953). He assumed that water did not 

 overtop the barrier — as if the dimension (h - D) were very large. An expres- 

 sion for the coefficient of transmission, C t , defined as the ratio of the 

 wave height in the lee of the structure, H t , to the incident wave height, 

 Hj , was developed as 



1 



1 + 



ttW sinh(2ird/L. ) 



L ± cosh[2ir(d - D)/L i ] 



(ID 



where L^ is the incident wavelength. This expression was displayed by Jones 

 (1974) for the special case of d = 60 feet (Fig. 2), using dimensional quanti- 

 ties rather than the dimensionless parameters to convey the impression of 

 sizes involved at prototype scale. Two depths of submergence (D = foot and 

 D = 5 feet) were evaluated to ascertain the decrease in the magnitude of the 

 transmission coefficient with increasing submergence. Jones (1974) indicated 

 that great errors are not introduced by ignoring small degrees of submergence. 



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