A Greedy Depth-Seeking Behavior for Energy-Efficient Transits by an Autonomous Underwater Vehicle

Abstract

An energy saving behavior is presented for autonomous underwater vehicles (AUVs) that uses greedy control decisions to take advantage of vertical gradients in ocean currents. The behavior relies on a dynamic vehicle model for motion and power consumption and environmental information that can be realistically obtained and processed onboard. Vehicle model parameters are consistent with a 12.75-in-diameter propeller-driven AUV. Simulation results are presented using a two-year tidally resolving ocean circulation model over three spatially distinct transits in the Southern California Bight. The energy saving behavior is compared to the common practice of transiting at fixed depth, as well as a “best case” scenario in which a vehicle has knowledge of the full-depth ocean current profile at its local position. The proposed behavior saves between 3% and 10% in energy expenditure depending on the vehicle's initial launch depth. On average, it is most efficient to initialize the vehicle at depths corresponding to the base of the surface oceanic mixed layer. Finally, a reduced order approximation of the optimal planning solution shows that the vehicle's depth choices oscillate with dominant tidal constituents for the region.