A Unified Guidance Framework for AUV Docking Operations

Author: Amirmehdi Yazdani

Yazdani, Amirmehdi, 2017 A Unified Guidance Framework for AUV Docking Operations, Flinders University, School of Computer Science, Engineering and Mathematics

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In the recent years, autonomous underwater vehicles (AUVs) have become a key tool for underwater surveys and explorations. A plethora of successful underwater missions and task allocations performed by AUVs such as detection, sampling, mapping, surveillance, and reconnaissance have been documented. The expanding mission scope for AUVs highlights the need for a long-endurance operational capability, which mainly depends on propulsion system efficiency and battery capacity. While there have been some significant improvements in battery energy density, the capacity to conduct long-term missions extended over many days to months is still not possible. This restriction imposes an extra cost of manned deployment and recovery to extend mission duration. The use of submerged docking systems permitting battery recharges and data downloads/uploads, is therefore essential to enabling persistence while reducing operational costs and hazards.

This thesis develops a systematic approach for analyzing underwater docking operations from the optimal control theory standpoint, and offers a robust and efficient docking guidance framework that can address the limitations of existing docking guidance solutions. This unified framework is established upon formulation of the twopoint boundary-value problem and utilizes well-known direct methods of calculus of variations to transcribe the conventional docking problem into an equivalent nonlinear

programming problem so that to generate optimal and tractable docking trajectories.

These methods include the inverse dynamics in the virtual domain and several pseudospectral computational techniques. The developed framework provides advanced flexibility and effectiveness enabling an AUV to compute not only openloop docking guidance solutions with no uncertainties, but also closed-loop (continuously-updated) control solutions with respect to situational awareness of operating environments and uncertainties associated with docking station poses, or docking with a moving station. The framework combines both homing and docking phases in one operation, and enables smooth and stable approach of an AUV into a

docking station while satisfying all realistic vehicular and environmental constraints and using minimum thrust and/or mission time in comparison with other existing docking algorithms.

The overall performance of the proposed guidance framework and particularly the capabilities and main features of the direct methods employed as the trajectory generator engines, are investigated through a series of docking scenarios in operating environments comprised of realistic currents and no-fly zone areas with respect to a priori known and unknown poses of docking station. The feasibility and robustness of trajectories from the standpoint of their realization on a real AUV are verified using a

high-fidelity software-in-the-loop simulation platform and Monte Carlo simulations. The new guidance framework developed in this thesis contributes to the cause of improving AUV autonomy by enabling longer mission durations while assuring reliable and cost-efficient docking operations.

Keywords: Autonomous underwater vehicle (AUV), Docking operation, Guidance system, Trajectory optimization

Subject: Engineering thesis, Computer Science thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Computer Science, Engineering and Mathematics
Supervisor: A/Prof.Karl Sammut