setting of the wave generator. The generator was adjusted to the desired 

 frequency, started, and waves generated for about 5 minutes; this constituted 

 a run. After shutdown of the wave generator, a necessary waiting period 

 followed in order to regain quiescent conditions in the wave tank. When these 

 conditions were attained, waves of another frequency were generated and this 

 process was repeated until all the desired wave periods for that stroke 

 setting were obtained; this process constituted a test. One, and sometimes 

 two, tests were completed per day, and the generator stroke was changed in the 

 afternoon so that a new test could be started the following morning. Wave and 

 force gages were calibrated both at the beginning and end of each day's 

 testing (and sometimes more frequently). 



IV. DATA REDUCTION AND ANALYSIS 



1 . Dimensional Analysis . 



For a particular breakwater and mooring system, the transmitted wave 

 height, H t , may be expressed as a function of the following variables: 



Hj. = f(H,L, B,D,G,X,m, k,e, d,y,v,g) 

 where 



e = horizontal excursion of the breakwater from its equilibrium position 



k = measure of mooring-system stiffness (equivalent spring constant per 

 unit length, X) 



m = mass of breakwater (per unit length, X) 



y = specific weight of water 



v = kinematic viscosity of water 



g = gravitational acceleration 



The remaining terms are defined in the definition sketch (Fig. 5). Since 

 this expression contains three dimensionally independent physical variables 

 (length, mass, time), this relationship involving 14 physical variables may be 

 replaced, according to Buckingham's ir-Theorem, by one involving 11 dimension- 

 less groups: 



— = wave transmission ratio, CL 



H c 



B G X ke .. 



D~ ' D ' D ' me = structure parameters 



H 



y = wave steepness 



32 



