The trapping of surface waves by submerged vertical porous and flexible barriers near the end of a semi-infinitely long channel of finite depth is investigated. The barrier configurations include a bottom-touching barrier and a surface-piercing barrier. For the bottom-touching barrier, the barrier is clamped at the bottom and is free at the upper end. While for the surface-piercing barrier, the barrier is clamped by a structure above the free surface and is free at the lower end inside the water. By matching the velocity and pressure along the barrier and along the gap and using the edge conditions, the full solutions are obtained.
In recent years, there is a tremendous interest in using partial barriers to control waves. Most barriers are extended from the bottom up to the water surface, while partial barriers only occupy a segment of the whole water depth. In coastal engineering, partial barriers as breakwaters are more economical and sometimes more appropriate for engineering applications. First of all, these kinds of breakwaters can provide a less expensive means to protect beaches exposed to waves of small or moderate amplitudes, and to reduce the wave amplitude at resonance. Especially, a bottom-touching partial breakwater not only resists the wave propagation but also allows the navigation of vessels over it. Meanwhile, a surface-piercing partial breakwater is especially suitable for deep-water applications, as wave energy concentrates near the water surface and no sea-bottom foundation work is needed. As a surface-piercing breakwater is comparatively fast to install, it can be used as a portable structure to provide temporary protection from wave attack. With the environmental concerns, the bottom-touching breakwater restricts the sediment transport and provides a strong protection against coastal erosion.
