47 research outputs found
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
Energy Based Control System Designs for Underactuated Robot Fish Propulsion
In nature through millions of years of evolution fish and cetaceans have developed fast efficient and highly manoeuvrable methods of marine propulsion.
A recent explosion in demand for sub sea robotics, for conducting tasks such as sub sea exploration and survey has left developers desiring to capture some of the novel mechanisms evolved by fish and cetaceans to increase the efficiency of speed and manoeuvrability of sub sea robots.
Research has revealed that interactions with vortices and other unsteady fluid effects play a significant role in the efficiency of fish and cetaceans. However attempts to duplicate this with robotic fish have been limited by the difficulty of predicting or sensing such uncertain fluid effects. This study aims to develop a gait generation method for a robotic fish with a degree of passivity which could allow the body to dynamically interact with and potentially synchronise with vortices within the flow without the need to actually sense them.
In this study this is achieved through the development of a novel energy based gait generation tactic, where the gait of the robotic fish is determined through regulation of the state energy rather than absolute state position. Rather than treating fluid interactions as undesirable disturbances and `fighting' them to maintain a rigid geometric defined gait, energy based control allows the disturbances to the system generated by vortices in the surrounding flow to contribute to the energy of the system and hence the dynamic motion.
Three different energy controllers are presented within this thesis, a deadbeat energy controller equivalent to an analytically optimised model predictive controller, a disturbance rejecting controller with a novel gradient decent optimisation and finally a error feedback controller with a novel alternative error metric. The controllers were tested on a robotic fish simulation platform developed within this project.
The simulation platform consisted of the solution of a series of ordinary differential equations for solid body dynamics coupled with a finite element incompressible fluid dynamic simulation of the surrounding flow. results demonstrated the effectiveness of the energy based control approach and illustrate the importance of choice of controller in performance
Modular Dynamic Modeling and Development of Micro Autonomous Underwater Vehicle: Lancelet
Ph.DDOCTOR OF PHILOSOPH
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
Control of Autonomous Underwater Vehicles
Autonomous Underwater Vehicles find extensive applications in defense organizations for
underwater mine detection and region surveillance. These are also useful for oil and
gas industries in detection of leakage in the pipelines and also in many other marine
industries. Underwater Robots can be categorized into two types namely (i) Remotely
Operated Vehicle (ROV) and (ii) Autonomous Underwater Vehicle (AUV). A ROV is a
remotely operated vehicle usually connected with the mother ship or base station through
a tethered wire whereas AUV is an Autonomous Underwater Vehicle which traverses
autonomously without any external interference. As opposed to ROV, control of an AUV
is difficult because it is an underactuated system (whose actuator inputs are less than the
number of degrees of freedom to be controlled), also the dynamics of AUV is influenced
by external disturbances such as ocean current and hydrodynamic effects. The motion
control problems of an AUV can be of different types such as path following, trajectory
tracking, waypoint tracking and also localization.
The thesis first develops path following control of a single AUV using the Serret-
Frenet(S-F) frame approach and error backstepping technique. Later on the same back-
stepping approach has been extended for implementation of formation control for multiple
AUVs.
Out of various motion control strategies, this thesis mainly focusses on path following
control problem of a single AUV. To address this problem of path following, a virtual frame
is considered. This virtual moving frame is called the S-F frame. The purpose of using
S-F frame is to represent the AUV kinematics in terms of virtual frame parameters. Then
a suitable control strategy has been developed which generates appropriate thruster force
and rudder orientation enabling the AUV to follow the desired path. In the thesis, the path
following controller has been developed using the concept of error backstepping method.
In the developed controller it is also shown that the path following error i.e. distance
between virtual frame and AUV actual frame approaches to zero and it is also ensured
that other states of the AUV remain stable and bounded. Although error backstepping
approach has been employed for path following problem but the earlier work [1] has not
considered the surge motion dynamics and coupling of rudder angle. Therefore, this thesis
has addressed the limitation of [1] and developed the backstepping controller considering
the rudder coupling term.
Although using a single AUV has many advantages but in case of its failure, the com-
plete mission may be affected. Further, the area coverage by an individual AUV is limited.
Thus, multiple AUVs are deployed for achieving a co-operative operation. Co-operative
working of multiple AUVs obviate the aforesaid disadvantages as the group of AUVs in
co-operative motion provides robustness in case of an individual AUV failure. Recently,
a lot of research has been directed on developing cooperative motion control of multiple
AUVs. Co-operative motion control can be achieved through different control strategies
such as Leader-Follower, Virtual Based structure and Behavior Based Formation Con-
trol. These cooperative control strategies have their own advantages and disadvantages.
Hence, these strategies have been reviewed and in this work, the concept of S-F together
with error backstepping approach have been exploited to develop formation control of
multiple AUVs. A fuzzy logic controller has also been implemented for deriving the con-
trol algorithm for leader-follower formation control scheme applied to control a group of
AUVs.
Subsequently, the thesis presents a graphical simulation environment using VRML and
SIMULINK3D to visualize the effect of controllers developed in providing the desired path
following and formation control activities of AUV(s). This graphical simulation accepts
the AUV states as inputs and represents the motion in an oceanic environment.
Also a proposal on hardware set up design of a single AUV is presented in the thesis.
The selection of necessary sensors, actuators and various electronics components for the
AUV hardware have been presented
Development of Path Following and Cooperative Motion Control Algorithms for Autonomous Underwater Vehicles
Research on autonomous underwater vehicle (AUV) is motivating and challenging owing to their specific applications such as defence, mine counter measure, pipeline inspections, risky missions e.g. oceanographic observations, bathymetric surveys, ocean floor analysis, military uses, and recovery of lost man-made objects. Motion control of AUVs is concerned with navigation, path following and co-operative motion control problems.
A number of control complexities are encountered in AUV motion control such as nonlinearities in mass matrix, hydrodynamic terms and ocean currents. These pose challenges to develop efficient control algorithms such that the accurate path following task and effective group co-ordination can be achieved in face of parametric uncertainties and disturbances and communication constraints in acoustic medium. This thesis first proposes development of a number of path following control laws and new co-operative motion control algorithms for achieving successful motion control objectives. These algorithms are potential function based proportional derivative path following control laws, adaptive trajectory based formation control, formation control of multiple AUVs steering towards a safety region, mathematical potential function based flocking control and fuzzy potential function based flocking control. Development of a path following control algorithm aims at generating appropriate control law, such that an AUV tracks a predefined desired path. In this thesis first path following control laws are developed for an underactuated (the number of inputs are lesser than the degrees of freedom) AUV. A potential function based proportional derivative (PFPD) control law is derived to govern the motion of the AUV in an obstacle-rich environment (environment populated by obstacles). For obstacle avoidance, a mathematical potential function is exploited, which provides a repulsive force between the AUV and the solid obstacles intersecting the desired path. Simulations were carried out considering a special type of AUV i.e. Omni Directional Intelligent Navigator (ODIN) to study the efficacy of the developed PFPD controller. For achieving more accuracy in the path following performance, a new controller (potential function based augmented proportional derivative, PFAPD) has been designed by the mass matrix augmentation with PFPD control law. Simulations were made and the results obtained with PFAPD controller are compared with that of PFPD controlle
Dynamic response and maneuvering strategies of a hybrid autonomous underwater vehicle in hovering
Thesis (S.M. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references (p. 87-93).The Odyssey IV autonomous underwater vehicle (AUV) is the next generation of unmanned subsurface robots from the MIT Sea Grant AUV Laboratory. The Odyssey IV AUV has a novel propulsion system, which includes a pair of azimuthing thrusters for maneuvering in surge and heave. An analytical model was developed to describe the complex nonlinear vehicle dynamics, and experiments were performed to refine this model. The fluid dynamics of unsteady azimuthing marine propulsors are largely unstudied, especially for small vehicles like the Odyssey IV AUV. Experiments suggest that thrust developed by an azimuthing propulsor is dependent on the azimuth angle rate of change, and can substantially affect vehicle dynamics. A simple model capturing the effects of azimuthing on the thruster dynamics is developed, and is shown to improve behavior of the model.The use of azimuthing thrusters presents interesting problems and opportunities in maneuvering and control. Nonlinear model predictive control (MPC) is a technique that consists of the real-time optimization of a nonlinear dynamic system model, with the ability to handle constraints and nonlinearities. In this work, several variations of simulated and experimental MPC-based controllers are investigated. The primary challenge in applying nonlinear MPC to the Odyssey IV is solving the time intensive trajectory optimization problem online. Simulations suggest that MPC is able to capitalize on its knowledge of the system, allowing more aggressive trajectories than a traditional PID controller.by Lauren Alise Cooney.S.M.in Ocean Engineerin
Cooperative localization for autonomous underwater vehicles
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009Self-localization of an underwater vehicle is particularly challenging due to the absence
of Global Positioning System (GPS) reception or features at known positions
that could otherwise have been used for position computation. Thus Autonomous
Underwater Vehicle (AUV) applications typically require the pre-deployment of a set
of beacons.
This thesis examines the scenario in which the members of a group of AUVs
exchange navigation information with one another so as to improve their individual
position estimates.
We describe how the underwater environment poses unique challenges to vehicle
navigation not encountered in other environments in which robots operate and how
cooperation can improve the performance of self-localization. As intra-vehicle communication
is crucial to cooperation, we also address the constraints of the communication
channel and the effect that these constraints have on the design of cooperation
strategies.
The classical approaches to underwater self-localization of a single vehicle, as
well as more recently developed techniques are presented. We then examine how
methods used for cooperating land-vehicles can be transferred to the underwater
domain. An algorithm for distributed self-localization, which is designed to take the
specific characteristics of the environment into account, is proposed.
We also address how correlated position estimates of cooperating vehicles can lead
to overconfidence in individual position estimates.
Finally, key to any successful cooperative navigation strategy is the incorporation
of the relative positioning between vehicles. The performance of localization
algorithms with different geometries is analyzed and a distributed algorithm for the
dynamic positioning of vehicles, which serve as dedicated navigation beacons for a
fleet of AUVs, is proposed.This work was funded by Office of Naval Research grants N00014-97-1-0202,
N00014-05-1-0255, N00014-02-C-0210, N00014-07-1-1102 and the ASAP MURI
program led by Naomi Leonard of Princeton University
Adaptive and extendable control of unmanned surface vehicle formations using distributed deep reinforcement learning
Future ocean exploration will be dominated by a large-scale deployment of marine robots such as unmanned surface vehicles (USVs). Without the involvement of human operators, USVs exploit oceans, especially the complex marine environments, in an unprecedented way with an increased mission efficiency. However, current autonomy level of USVs is still limited, and the majority of vessels are being remotely controlled. To address such an issue, artificial intelligence (AI) such as reinforcement learning can effectively equip USVs with high-level intelligence and consequently achieve full autonomous operation. Also, by adopting the concept of multi-agent intelligence, future trend of USV operations is to use them as a formation fleet. Current researches in USV formation control are largely based upon classical control theories such as PID, backstepping and model predictive control methods with the impact by using advanced AI technologies unclear. This paper, therefore, paves the way in this area by proposing a distributed deep reinforcement learning algorithm for USV formations. More importantly, using the proposed algorithm USV formations can learn two critical abilities, i.e. adaptability and extendibility that enable formations to arbitrarily increase the number of USVs or change formation shapes. The effectiveness of algorithms has been verified and validated through a number of computer-based simulations