An analytic method for the combined diffraction and transmission around a porous breakwater gap is presented. The method can be summarized as follows. First of all, it is necessary to decompose the incident wave into two components, according to the incidence angle and the permeability of the two breakwaters that form the gap. Then, let the breakwaters be completely transparent to the relevant component of the incident wave and ascertain the transmission field. Next, treat the breakwaters as solid to the other component of the incident wave and solve the diffraction field. Finally, superpose the transmission and the diffraction to give the objective wave motion. The available analytic methods for the diffraction by an aperture on solid wall are comparatively studied since they play the central role in working out the final solution of a real problem with combined diffraction and transmission. Sample computations are carried out for typical cases with both regular and irregular incidence. The computational results show that the phase effects of the porosity of the breakwaters on a combined wave field can be significant.
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