Tunable Wave Energy Converter Using Variable Inertia Flywheel

Axisymmetric heaving point absorbers are popular wave energy converters because of their easy deployment and insensitivity to incident wave directions. These devices are designed ideally to resonate with the incident wave to achieve high power output. However, as the device resonant frequency deviates from the dominant frequency of ever-changing irregular waves, the performance drops drastically. To solve this problem and as a complement to existing measures, we propose a mechanism, named variable inertia flywheel, to directly manipulate the equivalent mass of the point absorber, thus altering the system resonance frequency and power absorption bandwidth. We use a flywheel with symmetrically placed mass spring dampers in a ballscrew-based power take-off system. With its variable inertia and mass amplification effect, we can economically and dynamically adapt the system equivalent mass and corresponding parameters with small mass spring dampers. Apart from the passive configuration, we also propose the semi-active and active configurations to further enhance the performance and broaden the functionality scope of the proposed power take-off system. Numerical studies have revealed the dynamics of variable inertia flywheel, and have validated its adaptivity to varying wave conditions and its potential for increasing power output of point absorbers in both regular and irregular waves.