Application of Modal Expansion Method to Very Flexible Floating Structures (VFFSs)

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Abstract

This paper presents an application of modal expansion method to wave-structure interaction problem of Very Flexible Floating Structures (VFFSs), like Offshore Floating Photovoltaics (OFPV) membrane structures. In literature, the modal expansion method was applied to wave-structure interaction of Very Large Floating Structures (VLFSs), where wave amplitude and structure deformation amplitude were of the order of structure height. For VFFSs, wave and structure deformation amplitude could be of the order of ten times the structures thickness. In this study, we explore the applicability of the modal expansion method to this new field. The wave field is addressed by boundary integral equation using free surface Green’s function method and the structure deformation is approximated by structure vibration modes. Assuming small-amplitude wave and small structure motion, the coupling is achieved by solving the governing equilibrium equation based on the classic thin plate theory. The verification of the present method with respect to panel resolution and mode truncation is discussed. Structure displacements of numerical analysis are compared with experimental results. The comparison shows that the solution provides acceptable prediction for longer waves (wavelength is one-fifth of the structure length), whereas for shorter waves (wavelength is one-tenth of the structure length), obvious discrepancies occur, especially at the aft region of the structure.