Investigation on the wave energy converter that reacts against an internal inverted pendulum

In this work, a wave energy converter (WEC) that reacts against an internal inverted pendulum, which works as an inertial device to provide reaction for power absorption and is potentially superior due to its natural high elevation of the internal mass compared to a normal pendulum, named IPWEC has been studied. Optimal structural configurations of the WEC have been identified by a genetic algorithm. The equations of motion have been defined and solved explicitly using a linearized model, which has been validated by experiments and a non-linearized model. When comparing IPWEC with the WEC that reacts against a normal pendulum (NPWEC), it is found that, although both WECs present almost the same wave power capture ability, IPWEC possesses several advantages in most sea states due to the naturally high elevation of the pendulum's center of gravity: (1) the pendulum mass and the angular motion amplitude of the pendulum are 35% and 50%, respectively, smaller than those of NPWEC; (2) the averaged reactive power required under complex conjugate control is 75% smaller than NPWEC; (3) the moment which holds the pendulum fixed relative to the hull in the survival mode is merely a half as large as that of NPWEC.