Recharging autonomous underwater vehicles from ambient wave induced motions

In this paper a novel gyroscopic system capable of recharging an autonomous underwater vehicle (AUV) using wave energy is proposed. The system, which is based on control moment gyroscope (CMG) principles, utilises the gyroscopic response of a gimballed flywheel mounted within an AUV body to generate energy from the wave induced rotational motions of the vehicle. By utilising the wave induced rotational motions of an AUV and the relative motion/torque created by a precessing gimballed flywheel promises to enable AUVs to generate energy in-situ and from a renewable source. This novel approach has several advantages. As the system is housed internally it is not exposed to the harsh underwater environment, is not susceptible to bio-fouling and does not add any hydrodynamic drag. In addition, the system can be positioned anywhere within the AUV body and the technology has the potential to be developed into an integrated energy harvesting, storage and motion control system; whereby the wave induced gyroscopic precession of the flywheel can be used to generate energy, the flywheel kinetic energy (spin) can be utilised for energy storage (similar to Kinetic Energy Recovery Systems or KERS) and motion control can be provided by precession control of the flywheel (providing a stable platform for improved monitoring/recording capabilities). In this paper a theoretical description of the system is provided including a derivation of the governing equations of motion following a momentum (Newton-Euler) approach. A numerical model is also described and simulation results for a pitching 2m AUV system are presented. The results show that the system could be used to periodically recharge an AUV remotely, enabling longer AUV deployments at sea.