Design optimization and experimental validation of a two-body Wave Energy Converter with adjustable Power Take-Off parameters

Abstract

Wave energy is extracted from the motion of sea waves. The technologies to convert this energy into electricity have not yet reached maturity and there is no clear dominant design. In this work, a design methodology is proposed for a two-body Wave Energy Converter (WEC) with a novel configurable electromechanical Power-Take-Off (PTO) that allows setting its parameters for optimal power output according to wave conditions. A prototype has been modeled, designed and tested experimentally. It is intended for low power and energy self-sustainable applications, such as in telecommunications and data acquisition. This work addresses the modeling, optimal design, and parameter setting, to obtain maximum power output and efficiency for this class of WEC. A floating body is connected via the PTO to a submerged body in neutral buoyancy. If the PTO parameters are correctly set to match the external frequency of the waves, the system can operate close to resonance condition, which maximizes the generated power. Modeling a WEC can be extremely complex, so a linear mathematical model originally proposed by Falnes was adapted to find optimal PTO parameters for both regular and irregular waves. To validate the design model, tank tests were performed. Optimal PTO parameters in the WEC were determined experimentally. In the experiments, 16 cm high waves and 0.55 Hz of frequency were used to test multiple design parameters searching for optimal power output. Peaks of up to 20 W were generated with these waves. Extrapolating the experimental results, output power in the range of 400–600 W and an efficiency of 48.3% can be expected for 1 m high waves. The design model gives an acceptable prediction for the amplitude of the relative motion between bodies, the optimum damping coefficient of the PTO (c^pto), and the maximum generated power. The design model also makes a good prediction for the optimum stiffness coefficient (k^pto) for smaller values of the mass of the submerged body.