Hydrodynamic behaviour of floating polygonal ring structures under wave action

Abstract

In this paper, a semi-analytical method has been developed for the hydrodynamic analyses for floating polygonal ring structures under wave action. The considered polygonal shapes include equilateral triangle, square, pentagon, hexagon and circle where their geometries are created from a parametric equation involving cosine-type radial perturbation. For the similar wetted volumes of considered polygonal ring structures, the added mass, radiation damping and RAOs (Response Amplitude Operators) are similar but the wave exciting forces and wave fields inside the ring structures are somewhat different depending on their shapes, dimensions and orientations. Resonances occur at various frequencies associated with large wave amplitudes due to wave trapping inside the ring structures. By changing the dimensions of the ring structures such as the draft and the horizontal ring width, resonance frequencies may be shifted or reduced. Also, the orientation of polygonal ring structures has a significant influence on wave forces and wave amplitudes inside the ring structures; particularly for triangular and square ring structures. The semi-analytical solutions presented herein can be used as benchmark solutions for verifying numerical formulations and computer codes in determining hydrodynamic behaviours of floating polygonal ring structures.