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

Abstract

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. The different methods were used to assess the behaviour of the CCell WEC in a regular wave, with the calculations for mean power varying by 29.9% and the range of motion significantly under predicted by the simpler models. The coupled model increased the computational requirement by 12.3%, however it provided the developer a much deeper understanding of the impact on different hydraulic components.