The concept involved in theoretically predicting the performance of a two- 

 dimensional floating breakwater has been schematized by Adee, Richey, and 

 Christensen (1976) (Fig. 8). The incident wave approaches perpendicularly to 

 the long axis of the structure; part of the energy contained in the incident 

 wave is reflected, a part is lost through dissipation, and some of the wave 

 energy is transmitted beneath the breakwater. A part of the wave energy is 

 utilized in exciting motion of the breakwater, which is restrained by the 

 mooring system. The oscillations of the structure, in turn, generate waves 

 which travel away from the breakwater in both directions. The total trans- 

 mitted wave, hence, is the sum of the component of the incident wave which 

 passed beneath the structure and the leeward component generated by the 

 breakwater motion. The linear system representing this floating breakwater 

 analysis is shown in Figure 9. As long as the problem is linear, the com- 

 putation of the performance of the breakwater may be separated into three 

 parts: (a) formulation of the equations of motion, (b) solution for the waves 

 diffracted by a rigidly restrained breakwater, and (c) summation of the compo- 

 nents to obtain total transmitted wave. This provides the information of most 

 interest to designers — the total transmitted wave, motions of the structure, 

 and forces on the breakwater and in the mooring lines. 



The linear model formulation by Adee, Richey, and Christensen (1976) is 

 presented in the form of computer programs which calculate the hydrodynamic 

 coefficients, breakwater motions, and the wave field. These computer programs 

 determine the fixed-body parts of the transmitted and reflected waves by 

 computing the forces, moments, and waves which result when a rigidly fixed 

 body is struck by a sinusoidal incident wave of frequency, to. Motions are 

 found by computing the steady-state solution of the three components of the 

 equations of motion. The hydrodynamic coefficients and the waves generated by 

 the body motions are found by computing the forces, moments, and waves which 

 result when the body is forced to oscillate in still water in pure sway, pure 

 heave, or pure roll. 



77 x (X,1 



INCIDENT 



U>.'> 



iy HEAVE 



^ T (x,t) 



transm;tted wave 



Figure 8. Conceptual model of surface gravity waves approaching 

 a floating structure of arbitrary cross section (after 

 Adee, Richey, and Christensen, 1976). 



39 



