Oblique water wave scattering by a floating bridge fitted with a rectangular porous structure and the resulting waveload mitigation

Abstract

Scattering of oblique water waves by a floating bridge with rectangular porous walls fitted on its vertical sides in finite ocean depth is studied. An oblique water wave is assumed to interact with the structure and is partially reflected. The whole fluid region is split into five subregions in which two regions are porous regions, and the remaining three are water regions. The boundary value problems with respect to the velocity potentials are solved in all sub-regions by employing eigenfunction expansion technique. In order to figure out the reflection coefficients and hydrodynamic forces, a set of algebraic equations is formed from the appropriate matching conditions. Dispersion relation roots are analyzed and used in the system of linear equations. The effect of a number of parameters, such as the width of the porous wall, friction factor, angle of incidence, and draft of the bridge, on the reflection coefficients and hydrodynamic forces, is investigated. Porosity does not affect the reflection coefficient up to some certain value of the wavenumbers. The behavior of the reflection coefficient due to changes in the width of the porous wall is analyzed in order to choose appropriate width. It is noted that, because of the rectangular porous wall, a substantial amount of wave energy gets reflected back, and the waveload thus gets reduced on the floating bridge. All these observations lead to a suggestion of selection of suitable values of various parameters so that the reflection and forces acting on the floating bridge can be mitigated which will provide a safer working environment for the bridge. Graphs support all of our observations. The excellent agreement between our results and earlier results establish the validity of the present model.