Semi-analytical study of the first order horizontal force induced by oblique waves on the array of circular columns of offshore wind turbines equipped with permeable cylinders

Abstract

This paper studied the incident of linear oblique waves to circular columns of offshore wind turbines in conjunction with concentric and non-concentric thin permeable cylinders. The unique research objective of this work is to assess the possibility of using permeable vertical cylinders to reduce wave forces on the column of offshore wind turbines. The developed semi-analytical method benefits from the mathematical relation between Bessel functions to express the BEM-related integrals in the Fourier modes of the Hankel function and to calculate singular integrals indirectly. Moreover, Graf's addition theorem for Bessel functions was used for shifting between different coordinate systems to avoid calculating related integrals numerically. The basic geometries parameters such as permeability parameter, cylinders arrangement and the radius of the permeable cylinders, and the wavenumber on the horizontal wave-induced force were studied. The results are presented in graphs. The results indicate that covering the columns of DeepCwind and OC3 wind turbines with the permeable cylinders or using the permeable cylinders upstream helps reduce the horizontal wave-induced force at a particular permeability parameter. The results of this research are beneficial in the design of columns of offshore wind turbines and other structures with vertical piles, such as semi-submersibles.