Hydrodynamic analysis and optimization of a hinged-type wave energy converter - SeaWEED

Abstract

This thesis presents the experimental, numerical and optimization studies on a hinged-type wave energy converter, SeaWEED (SeaWave Energy Extraction Device), developed by Grey Island Energy. The device is considered as an improved attenuator consisting of four modules connected by adjustable truss structures. Extensive model tests of a 1:35 scale SeaWEED model with and without the power-take-off (PTO) units have been conducted at the towing tank of Memorial University (MUN). Friction dampers were designed to mimic the PTO systems. Repeated tests were carried out at a few wave frequencies around the region with maximum responses, and good repeatability has been observed. Potential-flow based time- and frequency- domain programs utilizing the Lagrange multiplier approach have been developed to simulate the dynamics of SeaWEED. In the time-domain program, nonlinear Froude-Krylov forces are calculated over the instantaneous wetted surfaces of the bodies under the wave profile, and the Wheeler Stretching method is applied to compute the wave pressure. The numerical results are compared with the experimental data, and good agreement is achieved. Optimization studies have been further conducted utilizing the frequency-domain program. Various parameters, including damping coefficients of the PTO systems, lengths of truss structures and the draft of the device, are considered. The uniform design method is used for sampling, and the response surface method is employed for surrogate construction. The desirability optimization method is utilized to optimize the response. An optimal combination of parameters is determined for an intended operation site.