behind the breakwater may be approximated by an arc centered at the middle of 

 the gap; crests to about six wavelengths may be approximated by two arcs, cen- 

 tered on the two ends of the breakwater and connected by a smooth curve 

 (approximated by a circular arc centered at the middle of the gap). Only one- 

 half of the diffraction diagram is presented on the figures since the diagrams 

 are symmetrical about the line x/L = 0. 



c. Waves Passing a Gap of Width Greater Than Five Wavelengths at Normal 

 IncidencT^ Where the breakwater gap width is greater than five wavelengths, 

 the diffraction effects of each wing are nearly independent, and the diagram 

 (Fig. 2-33) for a single breakwater with a 90° wave approach angle may be used 

 to define the diffraction characteristic in the lee of both wings (see Fig. 2- 

 53). 



Template Overlays 



Wave Crests 



Figure 2-53. Diffraction for breakwater gap of width > 5L (B/L > 5). 



d. Diffraction at a Gap-Oblique Incidence . When waves approach at an 

 angle to the axis of a breakwater, the diffracted wave characteristics differ 

 from those resulting when waves approach normal to the axis. An approximate 

 determination of diffracted wave characteristics may be obtained by consider- 

 ing the gap to be as wide as its projection in the direction of incident wave 

 travel as shown in Figure 2-54. Calculated diffraction diagrams for wave 

 approach angles of 0", 15°, 30°, 45°, 60° and 75° are shown in Figures 2-55, 

 2-56, and 2-57. Use of these diagrams will give more accurate results than 

 the approximate method. A comparison of a 45° incident wave using the approx- 

 imate method and the more exact diagram method is shown in Figure 2-58. 



e. Other Gap Geometries . Memos (1976, 1980a, 1980b, and 1980c) developed 

 an approximate analytical solution for diffraction through a gap formed at 

 the intersection of two breakwater legs with axes that are not collinear but 

 intersect at an angle. The point of intersection of the breakwater axes coin- 

 cides with the tip of one of the breakwaters. His solution can be developed 

 for various angles of wave approach. Memos (1976) presented diffraction 

 patterns for selected angles of approach. 



2-99 



