Wave Motion Over Two Submerged Horizontal Plates

With the construction of the port steps into the deep water area, the traditional breakwater is not applicable for economic and environmental conditions. So it is very significant to explore the special breakwaters with good performance of dissipating waves, which can be fit for the construction in deep water and low cost. One of them is the horizontal plate structure. So it is significant and application to study this structure.The horizontal plate structure allows free exchange of water mass through it and therefore is favored for the concerns of water quality in the sheltering region of the breakwater. In view of this, a new type structure was present in this article based on the previous studies and on considering reasonable use of materials. This breakwater consist two horizontal plates of different width. And this structure can be divided into two kinds:one is the short plate in the above of the structure; the other is the short plate below the structure. These two kinds of structure contain a variety of forms. Here we discussed three forms in each kind. From the experiment phenomenon we can see all structures have certain effect. Through the regular waves experiment, the relative width(W/L) and the H/L are discussed. We known that the value of almost have no influence on the reflection coefficient, especially in the second kind. Through reflection coefficient with the change of relative plate width, the first kind structure all can take to a minimum, this shows that this type of structure just have effect on certain frequency range of wave. The second structure's reflection coefficient increased with the relative plate width.Wave reflection and transmission over this breakwater is investigated analytically based on the linear potential wave theory. Through the characteristic function expansion method and velocity potential continuity conditions, the unknown coefficient can be obtained. The performance of the structure is compared with experiment and existed result with good agreements. The parameters such as plate width, water thickness, the submerged depth, the spacing between the two plates, and relative plate width are investigated and discussed. The variation of reflection and transmission coefficient alone with the above mentioned parameters are also presented. It is shown that the submerged depth and the long plate width is the main factors. It is significance of the multiple-layer breakwater to be the permanent structure in coastal engineering.