Study on the energy capture spectrum (ECS) of a multi-DOF buoy with MMR-PTO damping

The energy capture spectrum (ECS) is a valuable tool for evaluating and optimizing the performance of wave energy converters (WECs) under random waves. However, current methods used to measure the ECS can be timeconsuming and costly, which hinders its practical application. This paper proposes a novel method for calculating the ECS of WECs with complex power take -off (PTO) systems by defining the periodic energy capture matrix as an inherent parameter of the WECs. This parameter can be measured or calculated in pre-tests, thereby reducing subsequent cost and time. As a case study, a multi-DOF buoy with a mechanical motion rectifier (MMR) PTO system is investigated using this method. A numerical model is built with the open -source WEC-Sim software and is validated by an experimental test. The working mechanism of the MMR-PTO system is investigated, and the proposed ECS calculation method is compared with a previous method, demonstrating the accuracy of the proposed method. The energy capture characteristics of the multi-DOF buoy in the heave and free motion modes are also investigated and compared. The results show that the buoy in the free motion mode performs better in the high -frequency domain with a large PTO damping. The proposed method has the potential to promote the engineering application of the ECS and facilitate the performance optimization of WECs under random waves.