Hydroelastic Response of Very Large Floating Structures (VLFS) Connected With Wind Turbines

Abstract

Very large floating structure (VLFS) technology is a novel idea being introduced in ports and harbors, fishing, land reclamation, petroleum product storage facilities and so on. The flexible nature of VLFS makes the response hydroelastic and it is important to have a reduced response of VLFS. The term hydroelasticity refers to the action of hydrodynamic excitation over elastic body limits. The present study tries to examine the combined effect of horizontal loads of wind turbine tower along with the vertical hydrodynamic loads which question the stability of the performance of VLFS. This would lead to better understanding of the hydroelastic response of integrated wind farm-VLFS configuration. To examine the effect of relevant parameters on the VLFS hydrodynamic responses, motion amplitude transfer functions (RAO) for a wide range of wave frequencies are computed. Pontoon type VLFS are giant platforms resting on the sea surface, which are modeled by very large plates according to the Mindlin thick plate theory. The boundary integral element method (BIEM) is used to solve for the velocity potential using Laplace equation providing suitable boundary conditions. The fluid model is based on linear wave hypothesis. The effect of wind on wind turbines which are located at the edges and corner of the VLFS is investigated in the model. The Kaimal wind spectrum is used to generate time series of wind speed incident on the blades of the turbine and loads are computed using blade element momentum theory as in wind simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence). The finite element framework is used to develop the model and to find the hydrodynamic loading. Mooring line connections are used to reduce structural instability. In order to reduce the hydroelastic response of VLFS, connection with hinges or semi rigid line connections are observed to be effective. The elastic and dynamic effects of the combined wind-wave loading over the integrated VLFS are being considered. The hydroelastic effects of mooring lines will not be accounted for.