Interaction Of Waves With The Opening Straight Wall Breakwater

In the recent years, in order to diminish the wave reflection and the wave force, many countries have conducted researches to study new type of breakwaters instead of the solid conventional structure. The main emphases are focused on the perforated caissons. The perforated caisson breakwaters have considerable economic benefits, and the reflection rate of waves from breakwaters can be reduced. However, a detailed analysis and research on this type of structure is few because the interaction between waves and perforated caissons is extremely complex. In order to carry out safe and economical design, an accurate estimation of the reflection coefficient of perforated caissons and the wave force acting on perforated caissons becomes very important.Through 2D experiment in the wave flume, the interaction between waves and perforated caissons has been investigated. The physical model test was carried out in the wave tank for suspension material test at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. Regular and irregular wave parameters are selected in the range of engineering practice. The JONSWAP spectrum suggested by Goda is used to simulate irregular waves. The main factors influencing the reflection coefficient and the total force are considered in the test model design, such as the width of chamber, the porosity of perforated wall and the height of top cover. In order to compare with each other, the solid conventional structure, the perforated caisson without top cover and the perforated caisson with top cover were tested.The relationship between the reflection coefficient of perforated caisson without top cover and their effect factors are obtained, and it can be known that the influence of the relative chamber width is the most dominant factor. The reflection coefficient of perforated caissons with top cover is bigger than those without top cover. The phase difference between the total horizontal force and the total vertical force has been investigated, and the total vertical force reaches its extremum before the total horizontal force. The phase difference of crest values make for the stabilization of perforated caissons, on the contrary, the phase difference of trough values make against the stabilization.By use of the Ordinary Least Square Estimation, the empirical formulae of reflection coefficient, the phase difference between the total horizontal force and the total vertical force, the ratio of the total moment are presented for theoretical study and practical use. The results of empirical and the experimental data show the sound consistency with each other. Based on the experimental results, the influence of the top cover can be ignored when s/H>1.7, and the influence of the top cover must be considered when s/H< 1.7.