Studies on Wave Interaction with Composite Breakwater System

Abstract

In the present study, gravity wave dissipation due to the composite breakwater system consisting of porous structure with different configurations of vertical barriers, pile-rock porous structure with vertical barriers, multiple porous structure and barriers, submerged porous plate with bottom-standing and surface piercing porous structure, submerged porous structure with fully-extended barrier and submerged plate, and stratified porous structure backed by stepped obstacle is investigated under the assumption of small amplitude wave theory. The numerical investigation is performed using eigenfunction expansion method and orthogonal mode-coupling relation. The comparative study on specific structural configurations is performed using the physical model test to validate the numerical and experimental investigation. Further, validation of the numerical result is also performed with the results available in the literatures. Darcy’s law is incorporated for the flow through porous media and the porosity factor of the structure is introduced using the complex porous effect parameter. The composite breakwater system is studied for various parameters such as relative water depth, porosity of structure and barrier, structural thickness to wavelength ratio, water depth to wavelength ratio, submergence depth of the plate and gap between the structure and barrier. The study for the wave transformation due to submerged porous plate coupled with porous structure noted that, the wave damping due to the submerged porous plate backed by surface- piercing porous structure is more as compared to the submerged porous plate backed by the bottom-standing porous structure. In addition, the study on the coupled porous structures and submerged plate illustrates that, the increasing width of the fully-extended porous structure improves the performance of the breakwater system. The study on the stratified porous structure with stepped obstacle and porous block illustrates that the presence of the stratified structure decreases wave transmission and efficient wave attenuation can be easily achieved. The wave force acting on stratified structure is noted to be decreased if the structure is combined with wider surface-piercing porous blocks. Further, the presence of stratified porous structure combined with porous block helps in creating a tranquil zone in the leeside of the structure. The proposed study exhibits an informative result for the wave energy attenuation by different configuration of composite breakwater system which can be designed and implemented in coastal and harbour regions for achieving the tranquility.