The Impact of a Composite Rectangular Porous Breakwater in the Scattering of Water Waves by a Submerged Rectangular Tunnel

In this study, we investigate the problem of a submerged tunnel, protected by a thick porous breakwater placed over an impermeable step-like sea-bed which is an approximation of a slanting sea-bed, interacting with linear oblique waves. Further, the single thick breakwater is generalized by a composite breakwater consisting of [Formula: see text] strips, each with individual properties. The velocity potentials are obtained by adopting the separation of variables and the eigenfunction expansion methods in each of the [Formula: see text] sub-regions and applying the appropriate matching conditions across the vertical boundaries of the sub-regions, a system of linear equations is solved. This study reveals that increasing porosity by having a small porosity difference between the consecutive strips with the decreasing linearized friction term from left to right causes higher reflection and lesser transmission as well as less force. The reflection coefficient is enhanced, while the transmission coefficient decreases with the growth of the non-dimensional wavenumber. Smaller incident angles result in lower force components. The horizontal force increases with an increment of the tunnel height, whereas there is no significant change in the vertical force component. The impact of some other crucial parameters on the reflection coefficient, the transmission coefficient, and the associated wave forces acting on the tunnel is observed and recorded. Through the comparison made between our result and two established results, a good agreement for both cases is envisaged which suggests that the present model can be deemed efficient to be used for further engineering applications.