Ocean Current-Harnessing Stage-Gated MPC: Monotone Cost Shaping and Speed-to-Fly for Energy-Efficient AUV Navigation

TL;DR

The paper tackles the limited endurance of energy-constrained AUVs by introducing a Current-Harnessing Stage-Gated NMPC that forecasts ocean currents over the NP horizon and gates current-exploitation terms with a per-stage 'helpfulness' metric. The core innovations are a Monotone Cost Shaping term that provides a bounded energy rebate and a Speed-to-Fly term that nudges ground velocity toward the local current to enable gliding, both activated only when currents are advantageous and expressed in a smooth $C^1$ form. Through horizon-wise current sampling and a plug-and-play cost formulation, the method reduces energy consumption relative to a conventional MPC while preserving arrival times and constraint satisfaction in BlueROV2 simulations with Copernicus data. The results imply meaningful endurance improvements for battery-powered AUVs in realistic current fields, with practical implications for ocean exploration and offshore operations.

Abstract

Autonomous Underwater Vehicles (AUVs) are a highly promising technology for ocean exploration and diverse offshore operations, yet their practical deployment is constrained by energy efficiency and endurance. To address this, we propose Current-Harnessing Stage-Gated MPC, which exploits ocean currents via a per-stage scalar which indicates the "helpfulness" of ocean currents. This scalar is computed along the prediction horizon to gate lightweight cost terms only where the ocean currents truly aids the control goal. The proposed cost terms, that are merged in the objective function, are (i) a Monotone Cost Shaping (MCS) term, a help-gated, non-worsening modification that relaxes along-track position error and provides a bounded translational energy rebate, guaranteeing the shaped objective is never larger than a set baseline, and (ii) a speed-to-fly (STF) cost component that increases the price of thrust and softly matches ground velocity to the ocean current, enabling near zero water-relative "gliding". All terms are C1 and integrate as a plug-and-play in MPC designs. Extensive simulations with the BlueROV2 model under realistic ocean current fields show that the proposed approach achieves substantially lower energy consumption than conventional predictive control while maintaining comparable arrival times and constraint satisfaction.

Figures (13)

• Figure 1: The BlueROV2 "surfing" the ocean currents for energy-efficiency - Technical sketch of thruster layout.
• Figure 2: Oceanic Currents at 50 meters depth in the Aegean and Ionian Sea from the Copernicus Marine Service.
• Figure 3: (a) Top view of currents 100m depth south of Peloponnese, Greece. (b) Local 3D current grid in NED.
• Figure 4: Geometric intuition of $s_k$ "helpfulness" scalar.
• Figure 5: Thruster power consumption model fitting for 16V.