Steady-State Harmonic and Time Domain Point Absorber Modelling

This paper analysed the development of a steady-state harmonic model which, along the vertical axis, can simulate a single buoy’s motion with one degree of freedom (heave). The model can optimise a buoy’s geometric and control parameters to maximise power absorption from incident waves. The steady-state model revealed that at resonance, maximum power absorption of the buoy occurred in two region values with either low or high range of values of radiation damping coefficient (c2). In practice, achieving operation in the low c2 region is difficult. Therefore, it is recommended that the devices be designed to operate in the high c2 region to increase power capture. The model also revealed the best value for c1 (PTO damping coefficient) when the buoy with the peak frequency of the sea state is at resonance, and its mass is optimum. The PTO device size can therefore be manufactured accordingly to maximise power absorption. Out of all the tested buoy shapes (spike, bullet, and bi-cone), the bi-cone (60o/120o) buoy performed the best, and its response was most similar to the optimum mass response predicted by the model.