Dynamics of two floating wind turbines with shared anchor and mooring lines

Abstract

Floating wind farms present the opportunity to harvest wind resources located in deep water sites. Shared mooring designs can contribute in making floating wind energy more cost-competitive, and it is important to understand the new system dynamics that arise. We are presenting here HAWC2Farm, an extension of HAWC2 that can model multiple wind turbines with shared mooring lines. We apply the new modeling capabilities to simulate two 15 MW floating wind turbines on spar floaters with shared mooring lines. We consider two different sites and we identify and compare the natural frequencies and mode shapes of the shared mooring designs with those of an individual moored turbine. Furthermore, we investigate the influence of design parameters on the systems' natural frequencies and we show that it is possible for a shared mooring design to achieve similar characteristics as a single turbine design. Finally, we test the response of the shared mooring design in steady wind and regular waves and find that the surge displacement of the upstream turbine and its mooring line loads are considerably larger compared to the single turbine case.