Multi-vehicle cooperation and nearly fuel-optimal flock guidance in strong background flows

A multi-vehicle flocking and guidance control scheme is proposed for small autonomous underwater vehicles in the presence of strong ocean flows that exceed vehicles' actuation capabilities. The flocking problem and flock guidance problem are simultaneously addressed by enduing fluid properties to the vehicle swarm. This control scheme generates cohesive flocking behavior with inherent inter-vehicle collision avoidance and velocity consensus. The vehicle flock is guided along a fuel-optimal trajectory calculated for an individual vehicle based on background flow predictions, allowing us to compute a single optimal trajectory while still achieving robust flocking performance and near optimality for all vehicles. Resultant vehicle trajectories are nearly fuel-optimal when the spatial variation of background flow velocities across the flock is small. Dimensional analysis uncovers two important independent parameters dictating the balance between swarm compressibility and the degree of velocity consensus. The efficiency of the presented method is demonstrated in simulations with two synthetic background flow fields resembling realistic ocean flow patterns, and a flow field reconstructed based on ocean model data. A quantitative comparison with a generic artificial potential based control scheme shows that, owing to the inherent velocity consensus effect, the proposed method results in better flocking behavior and less actuation energy consumption.