Eccentric Rotating Wave Energy Converter

摘要

Our previous work on wave energy harvesting produced a design called Circular Sliding Wave Energy Converter (CSWEC), where a heavy sphere moved along a low-friction circular track that was mounted inside a surface buoy. The sphere was connected to a center-mounted generator by a thin rigid arm. As the buoy pitched and rolled, in response to ocean waves, the sphere rotated around the generator. In this new work, we propose to modify CSWEC by replacing the sphere, track, and arm combination with a heavy, semicircular solid disk that pivots around a center vertical shaft that spins the generator. This new design is called Eccentric Rotating Wave Energy Converter (ERWEC). The rotating semi-disk applies a torque on the cylindrical buoy, which increases the buoy rocking motions. Therefore, one may say that the rotating disk is an internal, natural exciter. We simulated the system dynamics with three second-order differential equations, one for the rotating eccentric disk and two for the buoy rocking modes. The results showed that the harvested power depends on the sea water damping on the buoy rocking motions and also on the generator damping, i.e., the power output (impedance). For a given wave condition, the power peaks at a certain damping; i.e., too much damping slows down the mass rotation and reduces power. We also observed that the ratio of rotor mass to total buoy mass should be large in order to achieve large rocking motions and power. Designing short natural rocking periods is beneficial for making the mass run fast and produce large power. We investigated the application of designing an ERWEC that could supply at least 1kw of power (and possibly supply electricity to an isolated island location). We developed a stable buoy system design, using practical parameters, and simulated its performance. For various combinations of parameters, we achieved 1-9kw of power in a random sea surface that was driven by a 20-kt wind speed.