Hydrodynamic Performance and Power Absorption of A Coaxial Double-Buoy Wave Energy Converter

As an important wave energy converter (WEC), the double-buoy device has advantages of wider energy absorption band and deeper water adaptability, which attract an increasing number of attentions from researchers. This paper makes an in-depth study on double-buoy WEC, by means of the combination of model experiment and numerical simulation. The Response Amplitude Operator (RAO) and energy capture of the double-buoy under constant power take-off (PTO) damping are investigated in the model test, while the average power output and capture width ratio (CWR) are calculated by the numerical simulation to analyze the influence of the wave condition, PTO, and the geometry parameters of the device. The AQWA-Fortran united simulation system, including the secondary development of AQWA software coupled with the flowchart of the Fortran code, models a new dynamic system. Various viscous damping and hydraulic friction from WEC system are measured from the experimental results, and these values are added to the equation of motion. As a result, the energy loss is contained in the final numerical model the by united simulation system. Using the developed numerical model, the optimal period of energy capture is identified. The power capture reaches the maximum value under the outer buoy’s natural period. The paper gives the peak value of the energy capture under the linear PTO damping force, and calculates the optimal mass ratio of the device.