Water wave interaction with a bottom-mounted wind turbine fitted with multiple porous rings.

Offshore wind farms play a crucial role in generating renewable marine energy. Therefore, a suitable design of the associated wind turbine is required to enhance the performance, longevity, and cost efficiency. Thus, in this work, we consider multiple horizontal porous rings attached to a bottom-mounted impermeable cylinder that resembles a wind turbine and study the wave diffraction problem. The wave action on the cylinder is studied by using linear water wave theory and solved by using the matched eigenfunction expansion method in the cylindrical coordinate system. The fluid domain is divided into multiple subregions with different vertical eigenfunctions in the respective regions. The eigenvalues obtained in the porous regions are complex numbers which satisfy the complicated dissipative-dispersion relation. The solution to this relation corresponds to locating the wavenumbers for which a non-trivial solution exists for a homogeneous system of equations, the order of which depends on the number of porous rings considered in the problem. For an incoming wave, the diffraction problem is then solved by using these eigenvalues and their associated eigenfunctions. The wave forces acting on the impermeable cylinder and the porous rings are evaluated by integrating the pressure difference. Finally, after validation of the considered model, numerical results are presented to observe the effect of the porosity, radii and draft of the rings and also of the water depth on different hydrodynamic coefficients. For numerical computation, three rings are considered. The key finding of this analysis is that a suitable choice of porosity distribution pattern to reduce the wave impact mainly depends on the radii of the porous rings and also of the impermeable cylinder. The wave run-up predominantly increases when the rings are placed very near to each other. • Multiple horizontal porous rings attached to a bottom-mounted impermeable cylinder are considered. • The structure resembles a wind turbine and we study the wave diffraction problem. • Complex eigenvalues in the porous regions satisfy the 'dissipative-dispersion' relation. • A sophisticated numerical algorithm is adopted to find those eigenvalues. • The effect of the parameters of the rings on different hydrodynamic coefficients is shown numerically. [ABSTRACT FROM AUTHOR]