Sean Kragelund

AUV Control and Communication using Underwater Acoustic Networks

Underwater acoustic networks can be quite effective to establish communication links between autonomous underwater vehicles (AUVs) and other vehicles or control units, enabling complex vehicle applications and control scenarios. A communications and control framework to support the use of underwater acoustic networks and sample application scenarios are described for single and multi-AUV operation.

AUV experiments in obstacle avoidance

Reactive obstacle avoidance (OA) is an important step in attaining greater autonomy in autonomous underwater vehicles (AUV). For AUVs that conduct underwater surveys, avoidance of uncharted obstacles can improve vehicle survivability. This paper discusses initial experiments at the Center for AUV Research in obstacle detection and avoidance using the Naval Postgraduate School ARIES AUV with the Blueview Blazed Array forward looking sonar. It includes a discussion on evaluating OA optimality, autopilot control design and sonar image processing. It concludes with a description of successful results from a recent demonstration

Control-Oriented Planar Motion Modeling of Unmanned Surface Vehicles

This paper describes a comparison of experimentally identified dynamic models for the planar motion of an unmanned surface vehicle (USV). The objective is to determine a model which is rich enough to enable effective motion planning and control, simple enough to allow straight forward parameter identification, and general enough to describe a variety of hullforms and actuator configurations. Starting from a three degree-of-freedom nonlinear model obtained from physical principles, we consider four simplified variants: (1) a linear model obtained by linearizing about straight, constant-speed motion, (2) a first order steering model (for turn rate) coupled with a first order speed model, (3) a second order steering model (for turn rate and sideslip angle), coupled with a first order speed model, and (4) a nonlinear model for low speed operation. The paper provides analysis of system identification data collected from field trials of three USV platforms in Summer 2010. The platforms represent three distinct control system implementations: a servo-actuated outboard engine, a servo-actuated jet-drive thruster, and differential thrusters.

Collaborative Unmanned Systems for Maritime and Port Security Operations

Abstract : This paper deals with some recent work ongoing at NPS, which attempts to show the utility of networked distributed vehicles for Maritime Interdiction, Riverine Operations, and related missions. We believe that these systems will be essential for dealing with the challenges in confronting these important National future needs.

Wireless Communication Networks between Distributed Autonomous Systems Using Self-Tuning Extremum Control

This paper represents an effective optimization approach for building high bandwidth wireless communication networks between distributed autonomous systems using unmanned aerial vehicles as airborne relay nodes. A self-tuning extremum control technique is developed to find an optimal location of the aerial vehicles to provide maximum communication throughputs. The idea behind the self-tuning control is to use an on-line gradient estimator to identify the derivative of a cost function and to use this as an input to a gradient-based hill-climbing algorithm. The on-line estimation of the gradient of a performance function is achieved by utilizing a perturbation-based peek-seeking approach which provides a quantitative gradient value of the cost function in a numerical way. Flight experiments are conducted to evaluate the performance of the proposed airborne wireless sensor networking control algorithm.

A MOOS-based online trajectory Re-planning system for AUVs

his paper describes an open source navigation system architecture for use in autonomous underwater vehicles. It is based on the Mission Oriented Operating System proposed, published and programmed by ( [1], [2]). It is uniquely applicable for work-in-progress type and development-stage software and capability installation onto an AUV system. This applicability is achieved by its completely modular nature, which is obtained by the operating system kernel running separate processes for each advanced navigation or control feature. Robustness is also achieved in this respect since failures and errors will cause only the individual modules that incurs them to fail. Such critical errors, bugs and failures will thereby be contained and their propagation halted from completely freezing even the low-level control loops and decision-making processes needed to successfully retrieve the malfunctioning AUV.

Issues in multi-agent search: False positives and Bayesian map updates

This paper explores the incorporation of false positives and Bayesian updates into the framework of optimal search. Optimal search is an open-loop optimal control framework developed by the US Navy to optimize search and rescue path planning for rapid sweep sensors such as sonar. Although useful as a pre-planning tool, this framework lacks features necessary for online planning, such as quantification of the role of detection events and subsequent probability map updates. This paper discusses these limitations and provides tools for implementing these features.

Sensor-based motion planning for autonomous vehicle teams

This paper employs a computational optimal control framework to develop a mission planning tool for a team of heterogeneous unmanned vehicles conducting a nominal mine countermeasures (MCM) mission. We first describe our motivation for developing vehicle-specific sensor models for unmanned surface and underwater vehicles working collaboratively to detect mines. Next, we describe the sonar detection models used to evaluate the performance of a long-range, forward-looking detection sonar and a high-resolution sidescan sonar deployed from these unmanned vehicles. Results from multiple computer simulations which highlight the flexibility and utility of this solution framework are presented.