0.2 0.4 



0.6 0.8 1.0 1.2 1.4 1.6 

 Structure Draft, D/L 



1.8 2.0 



Figure 13. Effect of mooring stiffness parameter on coefficient of trans- 

 mission for floating breakwater, W = (after Stiassnie, 1980). 



similar to that of the free breakwater, except in the region of D/L = 0.03 

 where a sharp decrease in C t is noted, and occurs as a result of resonance. 

 The behavior of the breakwater with a strong spring was generally similar to 

 that of a fixed plate. For the case of the medium spring coefficient, the 

 transmission is smaller than that for a fixed plate for D/L < 0.19. For 

 larger values, the transmission coefficient increases and reaches C t = 1.00 at 

 D/L = 0.67. According to Stiassnie (1980), the performance of the breakwater 

 with medium mooring is generally worse than for the condition with no mooring. 

 The varying results produced by the interaction of the mooring stiffness and 

 resonance phenomenon are difficult to anticipate without detailed analysis. 



(3) Influence of the Depth of Mooring Parameter . Stiassnie (1980) 

 determined the effect of the depth of the mooring point on the breakwater 

 performance by setting W = and k/ pgL = 1, and determined the transmission 

 coefficients and mooring force for three different points of attachment: 

 (a) mooring at the water surface, b/D = 0; (b) mooring at the midpoint of the 

 breakwater, b/D = 0.5; and (c) mooring at the lower edge of the breakwater, 

 b/D = 1.0. The effect of the mooring location on the coefficient of trans- 

 mission is presented in Figure 14; the effect on mooring force is shown in 

 Figure 15. According to Stiassnie (1980), the differences between the various 

 mooring depths are generally insignificant regarding both the transmission 

 coefficients and mooring forces. However, it was determined that mooring at 

 the lower edge of the plate allowed larger displacements (significantly larger 

 in the region where C t = 0) than the other two alternatives, as anticipated. 

 Despite the fact that Stiassnie's analytical treatment applies to that 

 configuration of floating breakwater which is probably the simplest possible, 

 10 different input parameters are still required (i.e., wavelength and ampli- 

 tude of the incident wave, L, - and H^/2, respectively; water density, p; 

 acceleration of gravity, g; draft of breakwater, D; depth of the center of 

 gravity, c; mass per unit width, m; moment of inertia, I c ; spring con- 

 stant, k; and depth of mooring point, b). 



43 



