The present paper deals with the development of a multi-purpose floating tension leg platform (TLP) concept suitable for the combined offshore wind and wave energy resources exploitation, taking into account the prevailing environmental conditions at selected locations along the European coastline. The examined Renewable Energy Multi-Purpose Floating Offshore System (REFOS) platform encompasses an array of hydrodynamically interacting oscillating water column (OWC) devices, moored through tensioned tethers as a TLP platform supporting a 10 MW wind turbine (WT). The system consists of a triangular platform supported by cylindrical floaters, with the WT mounted at the deck’s center and the cylindrical OWC devices at its corners. Details of the modelling of the system are discussed and hydro-aero-elastic coupling between the floater; the mooring system; and the WT is presented. The analysis incorporates the solutions of the diffraction; the motion- and the pressure-dependent radiation problems around the moored structure, along with the aerodynamics of the WT into an integrated design approach validated through extensive experimental hydrodynamic scaled-down model tests. The verified theoretical results attest to the importance of the WT loading and the OWC characteristics on the dynamics of the system.

This paper summarizes the coupled hydro-aero-elastic analysis of a multi-purpose floating structure suitable for offshore wind and wave energy exploitation. The analysis incorporates properly the solutions of the diffraction and the pressure- and motion- dependent radiation problems around the floating structure and the aerodynamics of a 5 MW Wind Turbine (WT). Finite water depths are considered, the structure being floating under the action of regular surface waves. The platform encompasses three hydrodynamically interacting Oscillating Water Column (OWC) devices consisting of concentric vertical cylinders, moored through tensioned tethers in a TLP concept. Details concerning the numerical and experimental modelling of the system are presented and the numerical results are compared against experimental data.

The purpose of this article is to investigate near trapped-mode occurrences by arrays of truncated cylinders. The basic question that this article tries to answer is whether near trapped modes (peak loading wave numbers) are indeed stimulated for arrays of truncated cylinders, such as in arrays of bottom-seated cylinders. Arrays of truncated cylinders are conceived as possible wave-energy-extraction mechanisms given that their modules are allowed to oscillate in surge (or sway) and heave, in contrast to bottom-seated cylinders, which are fixed. Hence, an additional question that should be answered is which actual mode of motion is important. To tackle these tasks, the governing hydrodynamic diffraction problem is considered. Different velocity potentials are defined for the liquid regions formed by the geometry of the truncated cylinders. The sought ultimate solution is achieved using the eigenfunction expansion technique combined with the direct approach, which, in contrast to the multiple-scattering method, is unquestionably more efficient and robust.

The purpose of this study is to scrutinize the coupled hydroaeroelastic problem for a TLP design of a floating structure consisting of multiple vertical truncated cylinders which support a $10 \mathrm{MW}$ wind turbine (WT). The platform is exposed to the combined effects of water waves and wind loading. The motions of the platform are examined for seven different directions of the incident waves. The hydrodynamic problem was solved analytically by combining the physical idea of multiple scattering and the method of matched axisymmetric eigenfunction expansions in order to obtain analytical representations of the velocity potential around the cylindrical members of the platform, while the contribution of the WT is considered within the six degrees of motion of the floater. Numerical results are initially presented for the exciting forces acting on the platform, the added masses, and the hydrodynamic damping coefficients, as well as the RAOs of the platform’s motions. Furthermore, the shear forces and bending moments are calculated at the point where the WT is assembled with the floater. Finally, results for the total mooring forces are given.

In order to investigate the hydrodynamic performances of semi-submersible type floating offshore wind turbines (FOWTs), particularly the effect of body-wave-current interaction, the OC4 FOWT is considered in the presence of co-existing regular wave and uniform current fields. The wind loads are not considered at this stage. The problem is treated in the framework of potential-flow theory in the frequency domain, assuming waves of small steepness, and the solution is obtained by using a perturbation expansion method for the diffraction potential with respect to the normalized current speed. Analytical and numerical formulations have been used to treat the inhomogeneous free-surface boundary condition involved in the hydrodynamic problem formulation for the derivation of the associated perturbation potential. The hydrodynamic loads were obtained after evaluating the pressure field around the multi-body configuration using three different computer codes. The results from the three computer codes compare very well with each other and with the numerical predictions of other investigators. Finally, the mean second-order drift forces are calculated by superposing their zero-current values with the corresponding current-dependent first-order corrections, with the latter being evaluated using a ‘heuristic’ approach.