Performance evaluation of a dual resonance wave-energy convertor in irregular waves

A new waterproof point absorber, named Dual Resonance wave-energy convertor (DR-WEC), is put forward in this paper. A geometry with low viscous effect is adopted for the waterproof outer floater of DR-WEC and two resonance frequencies can be found due to the existence of two sets of mass-spring subsystems. The motions and absorbed power of the DR-WEC in regular and irregular waves are investigated using the linear wave theory and the spectral analysis method with viscous effect being considered. The influence of three mechanical parameters, i.e., the internal mass, stiffness of spring and damping of power-take off (PTO) system, on the capture width ratio is studied. The mechanical parameters can affect the shapes of power response curves, which bring the possibility to enhance the wave power absorption by manipulating these parameters according to the characteristics of encountered waves. The Generalized Pattern Search (GPS) algorithm is employed to find these optimal mechanical parameters in both short-term and long-term sea states. The numerical results have confirmed that not all of the three mechanical parameters are needed to vary during operation. Some of the three parameters can be fixed for the balance of cost efficiency and wave power absorption. When the number of variable mechanical parameters is two, one, and zero, declinations of the annual average power relative to that with three are 4.1%, 13.0%, and 36.4%, respectively. At last, solutions for realizing an internal parameter-variable mechanism are discussed.