*Article* **Hydrodynamic Behaviour of a Floating Polygonal Platform Centrally Placed within a Polygonal Ring Structure under Wave Action**

**Jeong Cheol Park \* and Chien Ming Wang**

School of Civil Engineering, University of Queensland, St Lucia, QLD 4072, Australia **\*** Correspondence: jeongcheol.park@uq.net.au

**Abstract:** In this paper, a semi-analytical method has been developed for the hydrodynamic analysis of a floating polygonal platform that is centrally placed within a floating polygonal ring structure under wave action. In view to understand the wave interactions inside the ring structure, the formulation considers two cases: when the platform and ring structure oscillate individually, and when they oscillate together under wave action. The polygonal shapes of the floating structures can be created from a parametric equation involving the cosine-type radial perturbation. The formulation and computer code are verified by comparing the results with those obtained from the commercial software ANSYS AQWA. When floating ring structures are used, trapped waves are created in the inner water basin resulting in resonance. The interactions among the trapped waves, inner floating platforms and outer ring structures are investigated by performing parametric studies. By changing the dimensions of the platform and ring structure such as the drafts, the radii of platforms and polygonal shapes, their effects on major hydrodynamic quantities may be understood.

**Keywords:** 3D hydrodynamic analysis; resonance; floating polygonal structures; wave energy harvesting; cosine-type radial perturbation; eigenfunction expansion method
