170 research outputs found
A Unified Task Priority Control Framework Design for Autonomous Underwater Vehicles
In this thesis, we investigate the problem of bringing various behaviours of Autonomous Underwater Vehicles under a common control framework. Thereby, we propose a unified guidance and control framework for AUVs based on the task priority control approach. This incorporate various behaviors such as path following, terrain following, obstacle avoidance, as well as homing and docking to stationary and moving docking stations. The integration of homing and docking maneuvers into the task priority framework is thus a novel contribution of this thesis. This integration allows, for example, to execute homing maneuvers close to uneven seafloor or obstacles, ensuring the safety of the AUV by giving the highest priority to the safety tasks. Furthermore, the proposed approach tackles a wide range of scenarios without ad hoc solutions. Indeed, the proposed approach is well suited for both the emerging trend of resident AUVs, which stay underwater for a long period inside garage stations, exiting to perform inspection and maintenance missions and homing back to them, and for AUVs that are required to dock to moving stations such as surface vehicles, or towed docking stations. The proposed techniques are further studied in a simulation setting, taking into account the rich number of aforementioned scenarios
Simultaneous Trajectory Estimation and Mapping for Autonomous Underwater Proximity Operations
Due to the challenges regarding the limits of their endurance and autonomous
capabilities, underwater docking for autonomous underwater vehicles (AUVs) has
become a topic of interest for many academic and commercial applications.
Herein, we take on the problem of state estimation during an autonomous
underwater docking mission. Docking operations typically involve only two
actors, a chaser and a target. We leverage the similarities to proximity
operations (prox-ops) from spacecraft robotic missions to frame the diverse
docking scenarios with a set of phases the chaser undergoes on the way to its
target. We use factor graphs to generalize the underlying estimation problem
for arbitrary underwater prox-ops. To showcase our framework, we use this
factor graph approach to model an underwater homing scenario with an active
target as a Simultaneous Localization and Mapping problem. Using basic AUV
navigation sensors, relative Ultra-short Baseline measurements, and the
assumption of constant dynamics for the target, we derive factors that
constrain the chaser's state and the position and trajectory of the target. We
detail our front- and back-end software implementation using open-source
software and libraries, and verify its performance with both simulated and
field experiments. Obtained results show an overall increase in performance
against the unprocessed measurements, regardless of the presence of an
adversarial target whose dynamics void the modeled assumptions. However,
challenges with unmodeled noise parameters and stringent target motion
assumptions shed light on limitations that must be addressed to enhance the
accuracy and consistency of the proposed approach.Comment: 19 pages, 14 figures, submitted to the IEEE Journal of Oceanic
Engineerin
A COLLISION AVOIDANCE SYSTEM FOR AUTONOMOUS UNDERWATER VEHICLES
The work in this thesis is concerned with the development of a novel and practical collision
avoidance system for autonomous underwater vehicles (AUVs). Synergistically,
advanced stochastic motion planning methods, dynamics quantisation approaches,
multivariable tracking controller designs, sonar data processing and workspace representation,
are combined to enhance significantly the survivability of modern AUVs.
The recent proliferation of autonomous AUV deployments for various missions such
as seafloor surveying, scientific data gathering and mine hunting has demanded a substantial
increase in vehicle autonomy. One matching requirement of such missions is
to allow all the AUV to navigate safely in a dynamic and unstructured environment.
Therefore, it is vital that a robust and effective collision avoidance system should be
forthcoming in order to preserve the structural integrity of the vehicle whilst simultaneously
increasing its autonomy.
This thesis not only provides a holistic framework but also an arsenal of computational
techniques in the design of a collision avoidance system for AUVs. The
design of an obstacle avoidance system is first addressed. The core paradigm is the
application of the Rapidly-exploring Random Tree (RRT) algorithm and the newly
developed version for use as a motion planning tool. Later, this technique is merged
with the Manoeuvre Automaton (MA) representation to address the inherent disadvantages
of the RRT. A novel multi-node version which can also address time varying
final state is suggested. Clearly, the reference trajectory generated by the aforementioned
embedded planner must be tracked. Hence, the feasibility of employing the
linear quadratic regulator (LQG) and the nonlinear kinematic based state-dependent
Ricatti equation (SDRE) controller as trajectory trackers are explored.
The obstacle detection module, which comprises of sonar processing and workspace
representation submodules, is developed and tested on actual sonar data acquired
in a sea-trial via a prototype forward looking sonar (AT500). The sonar processing
techniques applied are fundamentally derived from the image processing perspective.
Likewise, a novel occupancy grid using nonlinear function is proposed for the
workspace representation of the AUV. Results are presented that demonstrate the
ability of an AUV to navigate a complex environment.
To the author's knowledge, it is the first time the above newly developed methodologies
have been applied to an A UV collision avoidance system, and, therefore, it is
considered that the work constitutes a contribution of knowledge in this area of work.J&S MARINE LT
Design of a Mobile Underwater Charging System
Autonomous Underwater Vehicles (AUVs) are extremely capable vehicles for numerous ocean related missions. AUVs are energy limited, resulting in short mission endurance on the scale of hours to days. Underwater Gliders (UGs) are able to operate on the order of months to years by using nontraditional propulsion methods. UGs, however, are unable to perform missions requiring high speed or direct forward motion due to the nature of their buoyancy driven motion. This work reviews the current state of the art in recharging AUVs and offers an underwater recharging network concept at a significantly reduced cost to traditional methods. The solution includes the design of a UG capable of serving as charge carrying agent that couples with and charges AUVs autonomously. The vehicle design is built on the work done previously at the Nonlinear and Autonomous Systems Lab on the development of ROUGHIE (Research Oriented Underwater Glider for Hands-on Investigative Engineering). The ROUGHIE2 design is a rethinking of the original ROUGHIE capabilities to serve as a mobile charger by increasing depth rating, endurance, and payload capacity. The recharging concept presented will be easy to adapt to many different AUVs and UGs making this technology universal to small AUVs
Underwater Vehicles
For the latest twenty to thirty years, a significant number of AUVs has been created for the solving of wide spectrum of scientific and applied tasks of ocean development and research. For the short time period the AUVs have shown the efficiency at performance of complex search and inspection works and opened a number of new important applications. Initially the information about AUVs had mainly review-advertising character but now more attention is paid to practical achievements, problems and systems technologies. AUVs are losing their prototype status and have become a fully operational, reliable and effective tool and modern multi-purpose AUVs represent the new class of underwater robotic objects with inherent tasks and practical applications, particular features of technology, systems structure and functional properties
Final Technical Report For The Enhancement Of Autonomous Marine Vehicle Testing In The South Florida Testing Facility Range
The purpose of this grant was to carry out the six scientific experiments on the South Florida Testing Facility (SFTF) Range. In addition to the enhancements to the range, work was performed on all six with some being successfully completed while research continues on the long term tasks
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