The flow resistance within the porous structure accounts for a 

 laminar and a turbulent contribution. Therefore, the theoretical 

 development may be used to shed some light on the important problem 

 of scale effects in hydraulic model tests with porous structures. 



2. Analytical Solution for Transmission and Reflection Coefficients 

 of Crib-Style Breakwaters . 



With the assumption of normally incident waves the problem to be 

 considered is illustrated in Figure 1. 



X = 



/ //////// 



v////////////// / 



Figure 1. Definition sketch. 



The rectangular porous structure is located between x=0 and x=S-j 

 i.e., the width of the breakwater is I. With the assumption of rela- 

 tively long incident waves described by linear long wave theory, the 

 equations governing the motion outside the structure are: 



, 3U 



h 77— 



o 8x 



(continuity) 



(1) 



and 



3U_ 

 8t 



^ = 



(conservation of momentum), 



(2) 



in which n is the free surface elevation relative to the Stillwater 

 level, h is the constant depth outside the structure, U is the 

 horizontal water particle velocity, g is the acceleration due to 



16 



