Submerged, Circular Slide Wave Energy Converters in Swell

At Oceans '13 in San Diego, we introduced the concept of a Buoy-based Circular Sliding Wave Energy Converter (BCSWEC), where a track was fixed to the inside of a floating "wave-rider" buoy, which pitched and rolled in response to waves. The system was adaptively tuned to changing environmental conditions with an artificial electro-magnetic spring in a control loop. At Oceans '18 in Kobe, we presented a "heave-enhanced" BCSWEC concept with three enhancements for efficiency and increased power. First, we moved the hermetically-sealed BCSWEC from inside to the outside of the buoy and attached it by 2 pivot points to allow tilts that are greater than those produced naturally by the sea surface. Second, we anchored the buoy to the sea bottom in shallow water. Third, we added a capability to significantly increase power by artificially increasing the magnitude of the pitch/roll motions by using a stiff external surface float on a moment arm. This achieved up to an order of magnitude more power, compared to the Oceans '13 design, in realistic ocean swell and random sea conditions. This new work describes a method to significantly increase the power over the heave-enhanced Kobe design by eliminating the buoy and extension arm and considering a wider set of float characteristics to include soft floats. For a specific set of WEC parameters in a typical swell environment, removing the extension arm increased the power by 50% (from 240w to 370w) and using a much softer float further increased the power by 100% (from 370w to 780w). Finally, we offer a procedure to stack a set of FCSWECs and show that the power increases proportionally with the number in the stack.