Understanding the force motion trade off of rigid and hinged floating platforms for marine renewables

In this work, we study the motion and loading response of a very large hinged floating platform. Such platform could host several floating marine renewable devices or alternatively, could extract energy through hinge motion. To this aim, we benchmark the response of a laboratory scale hinged platform to the motion and loading response of a rigid platform subject to regular waves. The hinged structure has two hinges and three pontoons, whilst the rigid structure is equipped with steel bars rather than hinges. The platforms are instrumented with motion detection spheres and the hinge assembly with strain gauges to measure vertical point loads. We find that the motion response of the hinged and rigid platforms is similar when the wavelength of the incoming wave is higher or smaller than the length of the platform. However, when the wavelength is similar to the length of the platform, single and triple sagging deformations occur for the rigid and hinged structures, respectively. In terms of loading response, we find significant load alleviation for the hinged structure when the wavelength is similar to the length of the platform. These insights reveal that very large hinged floating structures can contribute to offshore survivability by reducing loads in the structure. At the same time, the identification of motion behaviours are necessary to select operating configurations for mounted marine renewable devices.