Experimental investigation of breakwater-type WEC composed of both stationary and floating pontoons

Improving the energy conversion performance, especially in shorter waves, may enhance the competitiveness of wave energy converters (WECs) deployed at sea with medium wave conditions. In this paper, a novel system consisting of a front oscillating buoy type WEC and a rear fixed pontoon is proposed to improve the energy conversion performance of the original single pontoon breakwater -type WEC system by Ning et al. (2016). For the purpose of comparison, the experiments for both single pontoon system and two-pontoon system are conducted. Note that, to avoid the significant increase of the construction cost, the total pontoon volume (i.e., the displacement of the pontoon) of the proposed system remains the same with that of the single pontoon system. The two-pontoon system with different draft ratios d1/d2 (where d1 and d2 are the draft of the front pontoon and rear pontoon) are considered. The experiment shows that the system with smaller draft ratio gives more excellent energy conversion performance. The current controller-magnetic powder brake system is selected and used as the power take-off (PTO) system. The characteristics of the PTO system are investigated, which shows that the approximate Coulomb damping force can be simulated very well. The results also reveal that the proposed breakwater-type WEC with proper configuration improves the capture width ratio (CWR) effectively without compromising the coastal protection performance (i.e., the transmission coefficient KT < 0.5) in comparison with the single pontoon system. And the effective frequency range for the transmission coefficient (KT < 0.5) and CWR (η > 20%) can be broadened by improving the CWR in shorter waves.