Design, Dynamic Modeling, and Modal Analysis of an in-Situ Umbrella-Shaped Wave Energy Converter Through Experiment Validation

The absence of sustained energy supply presents a considerable challenge to ocean robots. A feasible solution to this problem is capturing wave energy. However, the actual wave condition is random, and the wave frequency is low, making the design of in-situ wave energy converters difficult. This article proposes an in-situ umbrella-shaped wave energy converter (U-WEC) based on the multibody structure that is optimized for natural frequency and has a centrosymmetric design. The structure can extract energy from low-frequency waves with a random incident direction. A nine-degree-of-freedom frequency-domain model that considers viscous damping force is established to analyze the motion response of the structure under wave excitation. Subsequently, the capability of U-WEC to capture energy from waves with low-frequency excitation and a random incident direction is demonstrated based on the results of modal and frequency response analyses. Furthermore, a wave tank experiment is conducted to obtain the actual motion response of the structure, and it confirms the reliability of the modal analysis and further verifies the superior energy capture performance of U-WEC. Results indicate that U-WEC can achieve an average energy capture power of 14 W under a wave condition with unit wave amplitude and a frequency of 1.25 rad/s (0.2 Hz). This article proposes a practical approach for designing in-situ omnidirectional energy-capturing structures suitable for conditions involving low-frequency waves.