Experimental study on trapezoidal pontoon-type floating breakwaters with attached porous plates

Abstract

In the present study, floating breakwaters (FBs) consisting of a trapezoid pontoon with attached porous plates are examined experimentally in deep water. A 2D experimental model has been carried out in the wave flume of the Research Institute for Subsea Science and Technology at IUT using regular waves. A total of 45 experiments have been performed to cover a wide range of sea state conditions and geometrical parameters such as wave height, wave period, breakwater draught, number of attached porous plates, porous plate height, the porosity of the attached plates, and also arrangements of porous plates. The results related to transmitted waves, mooring line force, and motion responses of the incident waves on the FB are presented. It is shown that the performance of the structure improves because of the attached plate, but not significant as in the case of FB with overall draught equal to that of the plate height. An increase in the number of attached porous plates under the breakwater may lead to a reduction of transmitted waves. The attached porous plate at the front of the FB with low porosity significantly enhances the hydrodynamic efficiency of FB. By increasing the porous plate height, the capability of the structure to reduce the wave transmission improves significantly, but the mooring line force and sway motion would increase. A new formula was developed to predict the transmission coefficient in trapezoidal FBs with at least two attached porous plates under the structure. Experimental data are in agreement with the results of the formula. In general, because using the attached porous plates results in reducing the wave transmission and also them being cost-effective, the use of attached porous plates under the structure in the design of FB could be considered the most efficient method.