Compared to large vehicles acting individually, platoons of small, inexpensive autonomous underwater vehicles have the potential to perform some missions that are commonly conducted by larger vehicles faster, more efficiently, and at a reduced operational cost. This thesis describes the power system of a small, inexpensive autonomous underwater vehicle developed by the Autonomous Systems Controls Laboratory at Virginia Tech. Reduction in vehicle size and cost reduces the accuracy of navigational sensors, leading to the need for autonomous calibration. Several models of navigational sensors are discussed, and the extended Kalman filter is used to form an observer for each, which are simulated and analyzed. / Master of Science

One of the largest design considerations for autonomous underwater vehicles (AUV's) that have specific mission scenarios is the propulsive efficiency. The propulsive efficiency affects the amount of power storage required to achieve a specific mission. As the efficiency increases the volume of energy being stored decreases. The decrease in volume allows for a smaller vehicle, which results in a vehicle that requires less thrust to attain a specific speed. The process of selecting an efficient propulsive system becomes an iterative process between motor, propeller, and battery storage. Optimized propulsion systems for mission specific AUV's require costly motor and propeller fabrication which may not be available to the designer. Recent advancements in commercially available electric motors and propellers allows for cost effective propulsion systems. The design space selection of motors and propellers has recently increased due to component demand of remote control airplane and boats. The issue with such systems is how to predict small propeller and small motor performance interactions since remote control motor and propeller designers usually don't provide enough information about the performance of their product. The mission statement is to design a propeller and motor combination that will allow an autonomous underwater vehicle to travel large distances while maintaining good efficiency. The vehicle will require 12 N of thrust with a forward velocity of 2 m/s. The propeller needs to be larger than 2.5â due to inflow velocity interaction and smaller than 4â due to loss of thrust when in surface transit due to suction. / Master of Science

Sweden is dependent on secure sea transport. Shorter disruption of imports of fuel and crude oil can be managed with an emergency stock, but a prolonged halt in imports creates problems. For industry, the vulnerability is greater. Fragmented production chains in combination with expenditure reductions in inventory causes a dependency on proper transport of intermediate goods in the manufacturing industry. A lengthy disruption thus involves disruption of production for both domestic consumption and for export goods containing imported parts.In order to secure shipping routes with a limited number of vessels, Mine Counter Measures (MCM) capacity is required, and according to the Armed Forces, developed with new sensors and autonomous vehicles. Sweden has acquired small AUV systems for MCM, and has plans to acquire larger and more advanced. Before any acquisition is implemented, a number of considerations have to be made. How does advanced AUV inflict on existing methods and systems? Is the result is better, is it faster, do we need to make adjustments? The essay aims to examine the military technology influence an AUV have on today's MCM operations. The results of the study can serve as part of the decision support for the Armed Forces and FMV before a purchase of an advanced AUV.The results of the thesis show that Advanced AUV:s, with the qualities they have , can affect the way the Armed Forces are conducting MCM today.

The use of counter-rotating propellers is often desirable for aerospace and ocean engineering applications. Counter-rotating propellers offer higher peak efficiencies, better off-design performance, and roll control capabilities. But counter-rotating propeller matching is a difficult and complex procedure. Although much research has been done on the design of optimal counter-rotating propeller sets, there has been less focus on predicting the performance of unmatched counter-rotating sets. In this study, it was desired to use off-the-shelf marine propellers to make a counter-rotating pair for a high speed autonomous underwater vehicle (AUV). Counter-rotating propellers were needed to provide roll control for the AUV. Pre-existing counter-rotating propeller design methods were not applicable because they all require inputs of complex propeller blade geometries. These geometries are rarely known for off-the-shelf propellers. This study proposes a new method for predicting the counter-rotating performance of unmatched propeller sets. It is suggested here that propeller performance curves can be used to predict counter-rotating thrust and torque performance. Propeller performance tests were run in the Virginia Tech Water Tunnel for a variety of small, off-the shelf propellers. The collected data was used to generate the propeller performance curves. The propellers were then paired up and tested as counter-rotating sets. A momentum theory based model was formulated that predicted counter-rotating performance using the propeller performance data. The counter-rotating data was used to determine the effectiveness of the method. A solution was found that successfully predicted the counter-rotating performance of all of the tested propeller sets using six interaction coefficients. The optimal values of these coefficients were used to write two counter-rotating performance prediction programs. The first program takes the forward and aft RPMs and the flow speed as inputs, and predicts the generated thrust and torque. The second program takes the flow speed and the desired thrust as inputs and calculates the forward and aft RPM values that will generate the desired thrust while producing zero torque. The second program was used to determine the optimal counter-rotating set for the HSAUV. / Master of Science

This work is focusing on a buoyancy system in anautonomous underwater vehicle, and the purpose is topresent a theoretical proposal on how the system indetail and in general can be changed to improve theaccessibility to its internal components and to make itmore robust. The largest part in this work is to simplify thehydraulic system, not only to make it more accessiblebut also to mitigate the risk of leakage due todifficulty of handling pipes and couplings. To reacha solution, interviews as well as litterature studieshas been made to identify specific problems. Thecollected data has then been discussed in order tocombine each specific solution to a final construction.The construction is presented with motivation, calculationsand 3Dmodels. The logical thoughts behind the finalconstruction are also presented for easy understanding ofthe choices being made. The design proposal differs from the earlier, two of themajor changes are that the old single direction the pump isreplaced with a new dual directional pump, and the valvemanifold is replaced with a single valve. In addition, allcomponents are now mounted in a chassis that can be easilylifted out from the hull, making the mounting and servicework on the system easier

The quasi-steady state-space models generally used to simulate the dynamics of underwater vehicles perform well in most steady flow scenarios, and are therefore acceptable for modeling today\'s fleet of endurance-focused autonomous underwater vehicles (AUVs). However, with their usage of numerous assumptions and simplifications, these models are not well suited to certain unsteady flow situations and for use in the development of AUVs capable of performing more extreme maneuvers. In the interest of better serving efforts to design a new generation of more maneuverable AUVs, a tool for simulating vehicle maneuvering within computational fluid dynamics (CFD) based environments has been developed. Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations are used in conjunction with a 6-degree-of-freedom (6-DoF) rigid-body kinematic model to provide a numerical test basin for vehicle maneuvering simulations. The accuracy of this approach is characterized through comparison with experimental measurements and quasi-steady state-space models. Three state-space models are considered: one model obtained from semi-empirical database regression (this is the method most commonly used in application) and two models populated with coefficients determined from the results of prescribed motion CFD simulations. CFD analyses focused on supporting the design of a general purpose AUV are also presented. / Ph. D.

This thesis explores the use of an Autonomous Underwater Vehicle (AUV) to track and pursue a tagged shark through the water. A controller was designed to take bearing and range to the shark tag and then control the AUV to pursue it. First, the ability of a particle filter to provide an accurate estimation of the location of the shark relative to the AUV is explored. Second, the ability of the AUV to follow the shark's path through the water is shown. This ability allows for localized environmental sampling of the shark's preferred path. Third, various path weightings are used to optimize the efficiency of pursuing the shark. This demonstrates that the proposed controller is efficient and effective. Fourth, the benefits of the addition of a second AUV are explored and quantified. The secondary AUV is shown to maintain formation without direct communication from the primary AUV. However, the communication of the AUVs increases the accuracy of all measurements and allows for future expansion in the complexity of the controller. Fifth, the effects of predicting the shark$'$s future movement is explored. Sixth, the effect of noise in the signal from the shark tag is tested and the level of noise at which the AUV can no longer pursue the shark is shown. This investigates the real world ability of the controller to accept noisy inputs and still generate the appropriate response. Finally, the positive results of the previous sections are combined and tested for various noise levels to show the improved controller response even under increased noise levels. To validate the proposed estimator and controller, seven tests were conducted. All tests were conducted on existing shark path data recorded by a stationary acoustic receiver and a boat mounted acoustic receiver. Tests were conducted on data sets from two different species of sharks, (Shovelnose and White) with two very different swimming behaviors. This shows the solution's flexibility in the species of shark tracked.

This thesis deals with the Simultaneous Localisation and Mapping algorithm as it pertains to the deployment of mobile systems in unknown environments. Simultaneous Localisation and Mapping (SLAM) as defined in this thesis is the process of concurrently building up a map of the environment and using this map to obtain improved estimates of the location of the vehicle. In essence, the vehicle relies on its ability to extract useful navigation information from the data returned by its sensors. The vehicle typically starts at an unknown location with no a priori knowledge of landmark locations. From relative observations of landmarks, it simultaneously computes an estimate of vehicle location and an estimate of landmark locations. While continuing in motion, the vehicle builds a complete map of landmarks and uses these to provide continuous estimates of the vehicle location. The potential for this type of navigation system for autonomous systems operating in unknown environments is enormous. One significant obstacle on the road to the implementation and deployment of large scale SLAM algorithms is the computational effort required to maintain the correlation information between features in the map and between the features and the vehicle. Performing the update of the covariance matrix is of O(n�) for a straightforward implementation of the Kalman Filter. In the case of the SLAM algorithm, this complexity can be reduced to O(n�) given the sparse nature of typical observations. Even so, this implies that the computational effort will grow with the square of the number of features maintained in the map. For maps containing more than a few tens of features, this computational burden will quickly make the update intractable - especially if the observation rates are high. An effective map-management technique is therefore required in order to help manage this complexity. The major contributions of this thesis arise from the formulation of a new approach to the mapping of terrain features that provides improved computational efficiency in the SLAM algorithm. Rather than incorporating every observation directly into the global map of the environment, the Constrained Local Submap Filter (CLSF) relies on creating an independent, local submap of the features in the immediate vicinity of the vehicle. This local submap is then periodically fused into the global map of the environment. This representation is shown to reduce the computational complexity of maintaining the global map estimates as well as improving the data association process by allowing the association decisions to be deferred until an improved local picture of the environment is available. This approach also lends itself well to three natural extensions to the representation that are also outlined in the thesis. These include the prospect of deploying multi-vehicle SLAM, the Constrained Relative Submap Filter and a novel feature initialisation technique. Results of this work are presented both in simulation and using real data collected during deployment of a submersible vehicle equipped with scanning sonar.

No description available.

The exploration of oceans and sea beds is being made increasingly possible through the development of Autonomous Underwater Vehicles (AUVs). This is an activity that concerns the marine community and it must confront the existence of notable challenges. These include, for example, mining minerals, inspecting pipeline and mapping oceans, sampling in contaminated water. Also, there has been another growing interest for security forces in precluding submarines or intruders from a beach or harbour entrance as well as hunting shallow water mines. However, an automatic detecting and tracking system is the first and foremost element for an AUV or an aqueous surveillance network. Since accurate surrounding information is essential in order to manoeuvre the AUV efficiently and economically, while corrupt information can jeopardize an entire mission. By extracting the space information form sensors, an AUV can achieve the localisation and mapping which are currently two primary concerns in the robotics research. Meanwhile, such information will provide a fundament of protection for surface vessels or troops, harbour infrastructure and oil plant against the enemy and terrorism. Acoustic sensors are commonly used to detect and position underwater obstacles, suspicious objects or to map the surroundings because sound waves can propagate more appreciable distances than electromagnetic and optical energy in the water. The measurements from these sensors, however, are always bound up with noises and errors. Various underwater activities may further pollute sound signals and then threaten the AUV navigation process. To simplify the detection procedure, some researchers make use of acoustic beacons or apparent obstructions (such as rocks, concrete walls) because they have distinctive characteristics. Point or line features are extracted from the acoustic signals or images for localization and mapping purposes. The long propagation range of sound waves can present new problems when acoustic sensors operate in confined environments, such as water tanks, rivers and harbours. The multiple reflections will be recorded by the sensor and result in false alarms. Furthermore, with advances in manufacturing techniques, the downsizing in marine explosive ordnances is progressing significantly, making it more difficult to discriminate between surface reflections and explosive ordnances. Finally, under the consideration of cost effectiveness, a mechanically scanned sonar has been introduced for the AUV in this research. However, the sensor beam cannot cover a large region simultaneously and a moving object may be distorted in the acoustic image because of the relatively low scanning speed. Due to such distortions in the data flows, objects may be indistinguishable from random noise or reverberation in acoustic images. The research presented here addresses the afore-mentioned problems relating to the theme of automatic detection from acoustic images. It is concerned with the detection and tracking of small underwater objects in order to protect autonomous underwater vehicles using sonar (SOund Navigation and Range). In the present study, these vehicles operated in laboratory water tanks or natural river environments. This research made use of self provided analytical studies that differentiated between reverberation and real object echoes. Detections were achieved automatically by using signal and image processing techniques. This research consists of three important and linked strategies. Firstly, a simple and fast reverberation suppression filter was provided, based on the understanding of the mechanism of the sonar sensor. Secondly, a robust detection system was developed to perceive small suspended obstacles in the water. Thirdly and finally, arc features were successfully extracted from the acoustic images and mathematical maps were generated from those features. The majority of experiments were derived from the elliptical water tank and the River Torrens, Adelaide, South Australia. For this project, a sequence of sonar images was taken from the same sonar location in the elliptical water tank. Further, a sequence of sonar images was taken from a sequence of sonar locations in the natural river. They provided different data sets for the assessment and evaluation of self developed algorithms. Results shown in this thesis confirm the favourable outcomes of the investigation and applied methodology. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1454839 / Thesis (M.Eng.Sc.) -- University of Adelaide, School of Mechanical Engineering, 2010