Underwater Vehicle Dynamics Research Articles

Robustness Aspects of a Multivariable Fuzzy Autopilot

This paper describes the development of a multivariable fuzzy autopilot for controlling the nonlinear yaw and roll dynamics of an autonomous underwater vehicle (AUV) model. The autopilot design is based on a new approach which uses a Gaussian fuzzy inference mechanism. Simulation results are presented which illustrate the robustness qualities of the design.

Robust nonlinear motion control for AUVs

We show how an efficient nonlinear controller for a general model of autonomous underwater vehicles (AUVs) dynamics, with uncertainties and external disturbances, can be designed by means of Lyapunov techniques. The control task we consider consists of tracking a given reference trajectory. As part of the design strategy, both model uncertainties and external disturbances physically corresponding to the effect of an underwater current are represented as a bounded perturbation of a nominal model of the vehicle dynamics.

A comparative study of control techniques for an underwater flight vehicle

Unmanned, underwater vehicles have been developed considerably in recent years. Remotely operated vehicles (ROVs) are increasingly used for routine inspection and maintenance tasks but have a range that is limited by the umbilical cable. For long range operations, such as oceanographic exploration and surveying, autonomous underwater vehicles (AUVs) are emerging which haveon-board power and are equipped with advanced control capabilities to carry out tasks with the minimum of human intervention. AUVs typically resemble torpedoes in that mosthave control surfaces and a single propulsion unit, and must move forwards to manoeuvre. Such vehicles are called flight vehicles. This paper describes techniques which are candidates for control of a flight AUV and identifies controllers used on some existing vehicles. Since underwater vehicle dynamics are nonlinear, fuzzy logic and sliding mode control were felt to have promise for autopilot application due to their potential robustness. Following development using a comprehensive simulation programme, the controllers were tested using the experimental vehicle, Subzero II, and their performance compared with that of a classical linear controller. The relative merits of the methods for practical implementation are discussed.

The ANFIS approach applied to AUV autopilot design

This paper describes the application of neurofuzzy techniques in the design of autopilots for controlling the yaw dynamics of an autonomous underwater vehicle. Autopilots are designed using an Adaptive-Network-based Fuzzy Inference System (ANFIS), a chemotaxis tuning methodology and a fixed fuzzy rule-based approach. To describe the yaw dynamic characteristics of an autonomous underwater vehicle, a realistic simulation model is employed. Results are presented which demonstrate the superiority of the ANFIS approach. It is concluded that the approach offers a viable alternative method for designing such autopilots.

Stabilization of underwater vehicle dynamics with symmetry-breaking potentials

We show how to stabilize, in stages, arbitrary steady translations of an underwater vehicle with feedback that derives from a potential and deliberately breaks symmetry in the dynamics. First, rotational symmetry is broken to ensure stability in the momentum parameters. Then, translational symmetry is broken to prevent drift. Stability of the closed-loop system is proved using the energy-Casimir method. A resulting property of the control law is robustness to model parameter uncertainty.

Analysis of an Underwater Vehicle's Model for Linearization and Control Purpose

In the present paper, a geometric-differential approach is employed to analyze the properties of a nonlinear model for the dynamics of Unmanned Underwater Vehicles. In particular, local accessibility, observability and feedback linearizability are investigated. The system is shown to be linearizable and a controller based on linearizing feedback and optimal control techniques is designed. Control performances and robustness properties of the control scheme are investigated by means of suitable simulations and discussed.

Stability and drift of underwater vehicle dynamics: Mechanical systems with rigid motion symmetry

This paper develops the stability theory of relative equilibria for mechanical systems with symmetry. It is especially concerned with systems that have a noncompact symmetry group, such as the group of Euclidean motions, and with relative equilibria for such symmetry groups. For these systems with rigid motion symmetry, one gets stability but possibly with drift in certain rotational as well as translational directions. Motivated by questions on stability of underwater vehicle dynamics, it is of particular interest that, in some cases, we can allow the relative equilibria to have nongeneric values of their momentum. The results are proved by combining theorems of Patrick with the technique of reduction by stages. This theory is then applied to underwater vehicle dynamics. The stability of specific relative equilibria for the underwater vehicle is studied. For example, we find conditions for Liapunov stability of the steadily rising and possibly spinning, bottom-heavy vehicle, which corresponds to a relative equilibrium with nongeneric momentum. The results of this paper should prove useful for the control of underwater vehicles.

Stability of a bottom-heavy underwater vehicle

We study stability of underwater vehicle dynamics for a six-degree-of-freedom vehicle modeled as a neutrally buoyant, submerged rigid body in an ideal fluid. We consider the case in which the center of gravity and the center of buoyancy of the vehicle are noncoincident such that gravity introduces an orientation-dependent moment. Noting that Kirchhoff's equations of motion for a submerged rigid body are Hamiltonian with respect to a Lie-Poisson structure, we derive the Lie-Poisson structure for the underwater vehicle dynamics with noncoincident centers of gravity and buoyancy. Using the energy-Casimir method, we then derive conditions for Lyapunov stability of relative equilibria, i.e. stability of motions corresponding to constant translations and rotations. The conditions reveal for the vehicle stability problem the relevant design parameters, which in some cases can be interpreted as control parameters. Further, the formulation provides a setting for exploring the stabilizing and destabilizing effects of dissipation and externally applied control forces and torques.

Modeling methods for underwater robotic vehicle dynamics

AbstractModels of the open‐loop dynamics for prototype Remotely Operated Underwater Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) are required for performance prediction and autopilot design. This article describes techniques which can be used to derive these models. The methods may be conveniently grouped into predictive techniques i.e., those which require only vehicle design data and which predict dynamics before the prototype is built and testing techniques i.e., methods which measure open‐loop dynamics from the trials performance of a prototype ROV. The relative benefits and drawbacks of the various methods are examined.

Systems Identification: Application to Underwater Vehicle Dynamics

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