Effect of varying PTO on a triple floater wave energy converter-breakwater hybrid system: An experimental study

A novel triple oscillating floater wave energy converter (WEC)-breakwater hybrid system was proposed to harvest wave energy and protect coast. A series of comprehensive laboratory experiments were conducted to investigate the effects of varying power take -off (PTO) and configuration of floaters on wave energy conversion and attenuation efficiency under regular and irregular waves. Wave energy reflection, transmission, loss and conversion are derived from experimental data to identify the optimum PTO damping force and draft of the floaters. It was found that as the initial draft gradient of floaters or PTO damping increases, the floater displacement and the wave transmission decreases, and the system makes the transition from a dissipative to reflective state. When the PTO damping of three floaters increases towards the wave maker, the wave energy absorption is largely determined by the draft gradient of three floaters, as the draft of each floater dictates the energy losses. In addition, the hybrid system with different PTO damping for each of the three floaters, exhibits an optimum frequency bandwidth for both wave power conversion efficiency (Ke exceeding 20%) and wave attenuation. Remarkably, the present WEC-breakwater hybrid system is capable to achieve high efficiency in wave power conversion and wave attenuation at the same time, particularly for irregular waves.