Performance analysis of two-body wave energy converters with a bistable mechanism and a mechanical motion rectifier in irregular waves

• Intra-well state of spring bistable mechanism induces PowerBuoy spar resonance • Larger hydrostatic stiffness of floats provides a good reference for relative oscillation • Natural frequency of WaveBob torus is tuned into spectrum peak in inter-well state • Larger interactive added mass and radiation damping enhance relative oscillation Various bistable mechanisms have been extensively investigated in wave energy utilization. However, there is little application of their physical realization in two-body wave energy converters (WECs) suitable for offshore regions. Therefore, this work proposes a physical realization of a spring bistable mechanism (SBM). The spring bistable mechanism consists of a pair of pressure springs in series on each side and is integrated into the WEC with a power take-off (PTO) based on a mechanical motion rectifier. The system dynamic model in time domain is developed and validated by the bench test. The dynamic characteristics and performance of the integrated WEC in irregular waves are analyzed and compared for different WEC types, translational PTO damping, spring bistable stiffness and wave conditions. The passive control of the SBM is discussed to uncover the effect of the SBM on performance enhancement. The results suggest that the output power per displacement volume achieves 16.2W/m 3 at the significant wave height of 0.1m for the WaveBob type WEC, which is superior to that for the PowerBuoy type WEC. The output power is improved by a maximum ratio of 16.33% for the WaveBob type WEC due to the large hydrostatic stiffness of the spar and adjustment of natural frequency of the torus by the SBM in inter-well state.