Abstract
This study investigates the performance of an oscillating surge wave energy converter (OSWEC) that utilizes adjustable geometry as a means of controlling the hydrodynamic coefficients, a concept originally proposed by the National Renewable Energy Laboratory. The body of the device is a bottom-hinged buoyant rectangular paddle with five horizontal flaps spanning the interior of the frame. The orientation of these flaps can be set independently about their center of rotation within the paddle. Changing the angle of attack of the flaps alters the hydrodynamic coefficients and natural frequency of the device as well as the ability to shed or absorb structural loads accordingly. This ability may allow the device to operate in a wider range of sea states than other current WEC designs. Results of numerical simulations and experimental testing of the OSWEC’s response to regular waves with all the flaps oriented at 0° (fully closed interior), or 90° (fully open) are presented. The numerical simulations were performed using WAMIT, which calculates hydrodynamic coefficients using boundary element methods (BEM) code to solve linear potential flow problems, and WEC-Sim, a Matlab-based tool that simulates multibody devices in the time domain by solving the governing equations of motion. A 1:14 scale model of the device was built for experimental evaluation in an 8-meter-long, 1-meter wide wave tank, which supports a water depth of 0.7 meters. The natural frequency and restoring force of the paddle was altered by the addition of springs in the direction of motion. The pitch motion was derived from measurements with displacement sensors. Comparison between the simulations and experiments are presented.