Abstract
The wave interaction with a vertical column shielded by an exterior porous shell is studied within the framework of potential flow theory. The structures are fixed rigidly at the sea bottom. The interior cylinder is impermeable, and the exterior shell is slightly porous and thin. Additionally, the exterior shell is assumed to have fine pores, and a linear pressure drop is adopted at the porous geometry. The mean drift wave force on the system is thereby formulated by two alternative ways, based respectively on the direct pressure integration, i.e., the near-field formulation, and the application of the momentum conservation theorem in the fluid domain, i.e., the far-field formulation. The consistency of the two formulations in calculating the mean drift wave force is assessed for the present problem. Numerical results illustrate that the existence of the porous shell can substantially reduce the mean drift wave force on the interior column. It also appears that the far-field formulation consists of a conventional part as well as an additional part caused by the energy dissipation through the porous geometry. The mean drift wave force on the system is dominated by the first part, which resembles that on an impermeable body. Local enhancements of the mean drift wave force are found at some specific wave frequencies at which certain propagation modes of the fluid satisfy a no-flow condition at the porous shell.
Highlights
A geometry with slots or pores can be used to enhance energy dissipation and in turn reduce the environmental impact
The porous geometry was commonly assumed to be with fine pores and thin in thickness
The mean drift wave force, which is of the second order from the perspective of the wave steepness, on a system consisting of an interior impermeable cylinder and an exterior porous shell is investigated
Summary
A geometry with slots or pores can be used to enhance energy dissipation and in turn reduce the environmental impact. Previous studies indicated that the linear wave force on an impermeable column can be reduced significantly by surrounding it with porous geometries (see Wang and Ren [15] for example). The mean drift wave force, which is of the second order from the perspective of the wave steepness, on a system consisting of an interior impermeable cylinder and an exterior porous shell is investigated. Solutions to the mean drift wave force on a vertical column shielded by an exterior porous shell have been rarely developed in the previous studies, and the research achievement in this study can help fill this gap.
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