Improving the performance of wave energy converters using a multi-dimensional floater driven by six parallel hydraulic cylinder

Multi-degree-of-freedom (multi-DOF) wave energy converters (WECs) may capture more wave energy compared to traditional single-DOF WECs. This study proposes a strongly coupled, parallel-driven multi-DOF WEC, named the 6-UPU WEC, which efficiently harnesses omnidirectional wave energy through a multidimensional moving body driven by six parallel hydraulic cylinder. The focus of this work is on deriving the forces from the hydraulic cylinder PTO system acting on the converter using the Newton-Euler method, and developing a nonlinear, strongly coupled dynamic model of the 6-UPU WEC based on WEC-Sim. Model tests were conducted in a wave tank to verify the validity of the numerical model. Using this numerical model, the motion response, power absorption, and array layout workspace of the 6-UPU WEC were investigated. Results show that at a significant wave height of 0.6 m and a wave period of 3.3 s, the energy capture efficiency of the 6-UPU WEC is improved by 11.5 % compared to a two-DOF WEC. Furthermore, the stability of workspace positions and their potential correlation with power capture were evaluated, indicating that a larger position ratio coefficient corresponds to better energy capture performance. The proposed 6-UPU WEC and the developed numerical model, which accounts for the coupled dynamic behavior of the six hydraulic cylinder. Systems, can provide effective references for the design of other complex multi-DOF WECs.