b 



■* — vwvf 



Figure 11. Floating vertical thin plate permitting development of 

 simple analytical expression of floating breakwater 

 response (after Stiassnie, 1980). 



u *-i.u 



-5*; 



\ 





W/L 





g 0.8 



0.00 







\ \ 



0. 01 





•H 







\ \ 



0.10 





■H „ _ 







• • * • Fixed Plate 





e 0.6 







\ \ 





_ 



<n 













§ 







\ \ 







u 







\ \ 







0.4 













o 





■ 



\ \ 











• 









<u 0.2 





• 









•H 













O 





« 









•H 













<H 





•i 









<H 0.0 





' 



• • .■ i i 



1 I I i i 





0.2 



0.4 



0.6 0.8 1.0 1.2 

 Structure Draft, D/L 



1.4 1.6 1.8 2.0 



Figure 12. 



Effect of mass parameter on coefficient of transmission for 

 floating breakwater, k = (after Stiassnie, 1980). 



The case W/L = 0.10 (which seems to be a reasonable upper limit for what may 

 be called a "thin" plate) has a trend similar to the curve for W/L = 0.00 but 

 with smaller numerical values. In Stiassnie 's example, the required draft 

 necessary to obtain CL = 0.50 is equal to D/L = 0.70, 0.57, and 0.13 for the 

 cases of W/L = 0.00, 0.10, and the fixed plate, respectively. Hence, very 

 large masses would be required to approximate the fixed plate. At D/L = 0.70, 

 an increase in the breakwater width by a factor of 10 will reduce the amount 

 of wave transmission by approximately 15 percent. Thus, Stiassnie (1980) 

 concluded, when considering a floating breakwater with a small mass, the 

 minimal mass required for structural integrity should be used. However, the 

 effect of the spring restoring force has been omitted from this comparison by 

 setting k = 0. This probably isolates the effect of the mass parameter on the 

 results, but the results may not be directly applicable to floating breakwater 

 design. 



(2) Influence of the Mooring Stiffness Parameter . The effects of 

 the spring stiffness were investigated by setting the plate width equal to 

 zero (W = 0) . Three different spring coefficients were considered: (a) k/pgL 

 = 0.01, a weak spring; (b) k/pgL = 1.00, a medium spring; and (c) k/pgL = 100, 

 a strong spring. The transmission coefficient under these conditions is 

 presented in Figure 13. The transmission coefficient for the weak spring is 



42 



