Wayne L. Neu

Cooperative localization of an acoustic source using towed hydrophone arrays

We describe field experiments in which a team of autonomous underwater vehicles cooperatively localize an acoustic source. The team implements a data fusion algorithm to enhance the localization performance of each individual vehicle and implements a decentralized motion control algorithm so that each vehicle maneuvers to minimize the joint localization error of the acoustic source. Each autonomous underwater vehicle is equipped with a custom-designed towed hydrophone array that measures the bearing angle between the array and the acoustic source. The noise statistics of the hydrophone arrays are state-dependent, and a generalized Kalman filter that accounts for the state-dependant measurement noise is utilized for localization.

Identification of a simplified AUV pitch axis model for control design: Theory and experiments

This paper presents an system identification algorithm for the longitudinal motion of a streamlined, tail-controlled, miniature autonomous underwater vehicle (AUV). The motion of a rigid body in six degrees of freedom is restricted to the dive plane to derive a fourth order dynamic pitch axis model. Based on the mechanical design of the vehicle, we impose symmetry and buoyancy assumptions that allow further model truncation. Basic dependencies between inherent stability of these truncated models and system parameters such as hydrodynamic coefficients are addressed. For the goal to rapidly design an AUV attitude control system, we experimentally show that it is sufficient to consider a second order dynamic model. We identify model parameters by matching the input and output behavior via least squares. Data collected during field trials validates both the system identification and the utility of a second order model for control design.

Development of a Dynamic Model of a Small High-Speed Autonomous Underwater Vehicle

A dynamic model is developed for a small, highspeed autonomous underwater vehicle. The vehicle has the unusual property of weighing up to 50 percent more than its displacement, and we seek to characterize requirements for steady-state flight imposed by the vehicless weight. The process of deriving a dynamic model, which is presented in a tutorial manner, highlights problems that arise when the dynamics of a submersible are expressed in terms of linear and angular momenta and combined with experimentally derived hydrodynamic coefficients

Hydrodynamic analysis, performance assessment, and actuator design of a flexible tail propulsor in an artificial alligator

The overall objective of this research is to develop analysis tools for determining actuator requirements and assessing viable actuator technology for design of a flexible tail propulsor in an artificial alligator. A simple hydrodynamic model that includes both reactive and resistive forces along the tail is proposed and the calculated mean thrust agrees well with conventional estimates of drag. Using the hydrodynamic model forces as an input, studies are performed for an alligator ranging in size from 1?cm to 2?m at swimming speeds of 0.3?1.8 body lengths per second containing five antagonistic pairs of actuators distributed along the length of the tail. Several smart materials are considered for the actuation system, and preliminary analysis results indicate that the acrylic electroactive polymer and the flexible matrix composite actuators are potential artificial muscle technologies for the system.

Design elements of a small AUV for bathymetric surveys

We describe the principal design elements of the Virginia Tech 690 autonomous underwater vehicle (AUV). The 690 AUV is designed for bathymetric surveys up to 500 m deep. It displaces less than 45 kg (100 lbs) and can operate for up to 24 hours at 4 knots.

Asymmetrical wake and propulsor effects on control surface effectiveness on AUVs

This study considers the influences of wake asymmetries and propulsor effects on the forces and moments created by control surfaces. Traditional quasi-steady state-space models developed for autonomous underwater vehicles (AUVs) tend to neglect these effects. Reynolds-averaged Navier-Stokes (RANS) simulations were used to assess the impact of asymmetrical inflow due to forward appendages as well as changes in the flow field created by an operating propeller on control surface effectiveness. For the AUV tested, substantial asymmetries in the flow field near the upper and lower rudders create significant differences in their respective performances. This discrepancy between the rudders has the potential to create considerable and unsuspected maneuvering reactions. The presence of the propeller was also seen to noticeably influence the performance of the control surfaces.

Design and testing of a Self-Mooring AUV

The Virginia Tech Self-Mooring AUV is capable of mooring itself on the seafloor. Its principal mission is to deploy bottom-mounted sensors without the need for a support ship to visit the mooring location. The mooring concept was previously demonstrated using a small-scale prototype. It has, more recently, been transitioned to a full-scale system and successfully demonstrated in the field. In this paper, we document the design of the full-scale vehicle and present results from field trials.

Design elements of a prototype self-mooring AUV

The Virginia Tech Self-Mooring Autonomous Underwater Vehicle (AUV) is capable of mooring itself on the seafloor for extended periods of time. The AUV is intended to travel to a desired mooring location, moor itself on the seafloor, and then release the mooring and return to a desired egress location. In addition, the AUV is designed to be inexpensive. The self-mooring concept was successfully tested on a small-scale platform known as the Virginia Tech 475 AUV. This report covers the major design elements of the self-mooring AUV, experiments that were conducted to refine the engineering analysis, and the results of successful field trials with this small-scale prototype.

Development of a Bio-Inspired Artificial Fish Using Flexible Matrix Composite Actuators

A bio-inspired prototype fish using the flexible matrix composite (FMC) muscle technology is developed for fin and body actuation. Flexible matrix composite actuators are pressure driven muscle-like actuators capable of large displacements as well as large block forces. An analytical model of the artificial fish using FMC actuators is developed and analysis results are presented. An experimental prototype of the artificial fish having FMC artificial muscles has been completed and tested. Constant mean thrusts have been achieved in the laboratory for a stationary fish for different undulation frequencies around 1 Hz. The experimental results demonstrate that a constant thrust can be achieved through tuning of excitation frequency. Free-swimming results show that the prototype can swim at approximately 0.9 m/s.Copyright

Multi-objective optimization of an autonomous underwater vehicle

A design optimization process for an autonomous underwater vehicle (AUV) is developed using a multiple objective genetic optimization (MOGO) algorithm. The optimization is implemented in ModelCenter (MC) from Phoenix Integration. It uses a genetic algorithm that searches the design space for optimal, feasible designs by considering three measures of performance (MOPs): cost, effectiveness, and risk. The synthesis model is comprised of an input module, three primary AUV synthesis modules, a constraint module and three objective modules. The effectiveness determined by the synthesis model is based on nine attributes identified in the US Navys UUV Master Plan and four performance-based attributes calculated by the synthesis model. To solve multi-attribute decision problems the Analytical Hierarchy Process (AHP) is used. Once the MOGO has generated a final generation of optimal, feasible designs the decision-maker(s) can choose candidate designs for further analysis. A sample AUV Synthesis was performed and five candidate AUVs were analyzed.