Model Tests and Simulations on a Wave Energy Converter Based on Inverse Offshore Engineering

This paper presents the initial simulations and model tests into the 'Green Water Concept' for wave energy conversion. Instead of reducing the motions and green water, as is done in normal offshore hydrodynamics, the 'Green Water Concept' tries to maximize the motions and green water through 'inverse engineering' to generate electric energy from the waves. First, results are presented of frequency domain calculations for the motion (de-) optimisation. Second, pilot model tests on the 'Green Water Concept' are presented. These tests also included the initial modelling of an electric and hydraulic Power Take Off (PTO). The accurate modelling of a PTO is an important aspect in testing of wave energry concepts numerically and in a wave tank: at the moment that energy is converted into electricity in the PTO, the hydrodynamic behaviour of the structure is changing. The tests confirmed the high motions and large amount of green water of the 'Green Water Concept' as predicted in simulations. For the present concept, a mean power (at full scale) close to 1 MW was generated in a regular wave of H = 3.0 m for the maximum possible setting in the chosen test set-up. This setting was limited by the chosen mechanical and electric motor set-up in this pilot test series, not the actual maximum of the 'Green Water Concept' itself. Considering the test results, it is clear that the potential of the system is significantly larger.