Breakwater 

 ncoming Wave Crest 



Figure 2-60. Wave diffraction pattern behind an offshore 

 breakwater three wavelengths long for waves 

 approaching at a 30° angle. 



numerical computer solutions to the offshore structure diffraction problem for 

 structures of arbitrary planform. Better accuracy in proximity to the struc- 

 ture and definition of the reflected wave field in front of the structure are 

 given by these solutions. 



g. Diffraction of Irregular Waves . The preceding discussions of diffrac- 

 tion phenomena deal only with monochromatic waves. Waves in the real world 

 are usually made up of many components having different periods or frequencies 

 (see Ch. 3). The combination of wave heights and frequencies present in the 

 sea forms what is termed a wave spectrum. For a wave spectrum, each wave fre- 

 quency is diffracted in accordance with its local wavelength. For diffraction 

 around offshore breakwaters, the handlike pattern of Figure 2-59 will not be 

 well defined because of the range of phase differences among the many wave 

 components propagating around each breakwater tip. Diffraction of irregular 

 waves by a breakwater gap has been studied by Wiegel, Al-Kazily, and Raissl 

 (1971), Raissi and Wiegel (1978), and Goda, Takayama, and Suzuki (1978). The 

 study by Goda, Takayama, and Suzuki takes into account an initial spreading of 



2-108 



