Point absorber wave energy converter is one of the most effective wave energy harness devices. Most of the wave energy converters generate energy by oscillating the floating body. Usually, the power-take-off system is simplified as a linear spring and a linear damper. However, the narrow frequency bandwidth around a particular resonant frequency is not suitable for real vibrations applications. Thus, a nonlinear hardening spring and a linear damper are applied in the power-take-off system. The bandwidth of hardening mechanism is discussed. The dynamic model of wave energy converter is built in regular waves with time domain method. The results show that the nonlinear wave energy converter has higher conversion efficiency than the linear wave energy converter more than the natural frequency state. The conversion efficiency of the nonlinear wave energy converter in the low frequency state is closed to the linear converter. The amplitude of the incident wave, the damping of the nonlinear wave energy converter and the nonlinear parameter [Formula: see text] affect the energy capture performance of the wave energy converter.

Under the impacts of waves and other marine environment, the jacket offshore platform has an obvious vibration and generates lots of energy. Meanwhile, the platform may suffer fatigue damage. The vibration energy harvesting of a jacket offshore platform under random waves with a nonlinear energy sink (NES) was investigated, and a NES-Energy harvester (NES-EH) was then designed by combining an electromagnetic linear generator with the NES. Moreover, the dynamic model of the NES-EH-offshore platform was built, and the electromagnetic damping and stiffness of the energy harvester were optimized by analyzing the energy capture efficiency and root mean square reduction of the platform displacement. The effects of NES nonlinear stiffness and damping, peak period and effective wave height of irregular waves on the capture power and width of the NES-EH were also analyzed. The results show that nonlinear stiffness and damping of the NES impact the energy capturing efficiency of the NES-EH; the smaller the damping and nonlinear stiffness, the higher the power captured by electromagnetic damping in the NES-EH. Compared with NES, the NES-EH system has a better effect on the vibration control of the platform and can better capture considerable vibration energy.