Scattering of short-wave groups by submerged horizontal plate

A fully submerged horizontal plate has been suggested as a breakwater. With a proper design in the length, thickness, and submerged depth of the plate, most of the incoming short waves can indeed be reflected. The method of eigenfunction expansion is used to solve for the reflection and transmission of the short waves. The present results agreed with earlier experimental data and computations. If the incident wave is Dichromatic, a second-order long wave train accompanies the wave groups. This long wave train is also scattered by the horizontal plate. It is shown here that the scattered long waves exist on both sides of the horizontal plate even when the short waves are completely reflected. The long waves may prove to be a bigger hazard than the short waves, because the wave period of the long wave (1-3 min) is closer to the natural frequency of coastal structures.