Multi-degree-of-freedom decoupled mechanism for improving energy harvesting performance of wave energy converter

The multi-degree-of-freedom wave energy converter (MDWEC) has attracted much attention due to its potential to efficiently harvest wave energy. However, current designs of MDWECs seldom consider coupled motions between the floating body and the power take-off (PTO), resulting in a loss of energy harvesting efficiency. To bridge this research gap, this paper explores the decoupled mechanism of active drive mechanical structures used for the MDWEC energy harvesting scenario. This decoupled mechanism enables the operating axes of PTOs to align one-to-one with the motion degree-of-freedom (DOF) of the floating body, thereby overcoming the energy harvesting efficiency limitations of the MDWEC caused by the coupled motion. To illustrate this idea, a novel multi-DOF decoupled wave energy converter (MDD-WEC) is presented according to real wave site conditions. A multi-physical-domain numerical model is developed. According to the Froude criterion, the reduced-scale prototype is constructed, and the numerical model test is performed in a wave tank. The proposed structure’s motion response amplitudes obtained from wave tank experiments and numerical simulations under two irregular wave conditions showed relative errors below 5 %, confirming the numerical model’s accuracy. Based on this, multi-PTO parameter analysis is subsequently performed to reveal the effects of different PTO configurations on the energy harvesting performance of the MDD-WEC. Benefiting from this characteristic, each PTO in the MDD-WEC can be independently optimized to absorb more wave energy according to wave conditions. The performance comparison results demonstrated that, compared with the point absorber WEC and the parallel configuration WEC with multi-DOF, the proposed MDD-WEC increases the capture width ratio (CWR) by 72.5 % and 39.3 % under regular wave conditions, respectively, and by 60.8 % and 32.9 % under irregular wave conditions.