Coupled modelling of a non-linear wave energy converter and hydraulic PTO

The mechanical motion of a wave energy converter (WEC) is converted by the power take-off (PTO) system into electricity, but these two systems are not independent, as they have been treated in WEC modelling. Treating them as such leads to inaccuracies in prediction of power output and reliability, and can erode confidence in numerical modelling tools. This paper presents a methodology for the two-way coupling of high fidelity modelling of WEC hydrodynamics with a more accurate representation of the PTO and investigates the impact of using simplified PTO models. Simplified models represent the full PTO with a single parameter which is in itself difficult to choose and may require a number of iterations. These different methods were used to assess the behaviour of the CCell WEC in a regular wave, with the calculations for mean power varying considerably in different wave conditions and the range of motion consistently under predicted by the simpler models. The coupled model increased the computational requirement for the simulation, however it provided the developer a better understanding of the impact on and utilisation of different hydraulic components.