Experimental validation of the mooring system of a Wave Energy Converter

Energy transition is one of the main concerns of modern society: a decarbonisation of the energy sector is required. Among the alternative solutions, ocean energy is of particular relevance. Ocean technologies are not yet ready to be commercialised due to the difficulty of analysis and high costs but they are characterised by a continuous development thanks to encouraging results. For these reasons they represent, at the same time, a challenge and a promising field of investment in modern society. To study the potential of this new frontier reliable models are necessary. A validation of experimental data must be achieved to verify the level of stability of these models. The aim of this thesis is to analyse the mooring system of the Wave Energy Converter ISWEC, a device whose objective is to produce electrical energy by converting the kinetic energy owned by the sea waves. To study the cable dynamics of the mooring system two software packages were used: a lumped-mass mooring module called MoorDyn and a FEM one named MooDy. A detailed comparison was done considering the capabilities of the software, the computational cost and the results obtained from the simulations. Experimental data from the test campaign performed at the Hydrodynamic and Ocean Engineering Tank in Nantes (LHEEA), presented for the Marinet2 project, were investigated. An ISWEC scaled model was tested in the tank as a first step of the design process, both under regular and irregular waves. A proper set-up of the model was built with both MooDy and MoorDyn to simulate experimental data. To obtain a validation of the results, the full hull’s model DoF framework was properly rescaled to meet the requirements of the evaluation of the full scale ISWEC model, which is located at Pantelleria, Italy. The model was stabilised and a verification of the output was performed. A comparison of the data obtained with the numerical models was provided. It was observed that MoorDyn achieves a better trade-off between accuracy of results and computational cost.