Motion and force response of a hinged and rigid flat floating platform for offshore wind

In this work we present the motion and force response of a novel hinged flat floating platform compared to the response of a more traditional rigid flat floating platform. We investigate the response of the platforms through experimental tests and numerical simulations. The experimental tests are performed in the Kelvin Hydrodynamics Laboratory at the University of Strathclyde. The hinged platform is built with three floaters joined by two hinges. Whilst the rigid platform is fabricated by replacing the two hinges with rigid steel bars. The platforms are instrumented with motion detection spheres and with strain gauges at the hinge points. The numerical model is a hydromechanical model that considers multibody hydrodynamics coupled to hydroelastic considerations via beam theory.

We find three regimes of motion response at low, intermediate and high frequency waves. At low frequency range, the platforms ride the wave. At intermediate frequency the hinged platform presents double sagging, whilst the rigid platform shows single sagging. At high frequency, most of the motion is concentrated at the upstream side of both platforms. We confirm the motion response regimes with the hydromechanical model. We find that there is a trade-off between motion and force response. Although the hinged platform experiences higher displacements than the rigid counterpart, it also provides significant load alleviation at the hinges. Hence, it is envisioned that hinged platforms could become an alternative to deploy multiple offshore wind turbines. Whilst good characterisation of motion response can help in designing wind turbines that can cope with the range of motions of the hinged platform.