Thesis (Sc. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1987. / "January 1987." Bibliography: p. 193-200.

The aim of this research is to establish a measurement system to acquire 2-D sound scattering field by an underwater target. In the system, A 3-DOF (degree of freedom) block is remotely orientated by Borland C++ Builder programming language and the batch-processing for signals is used to estimate strength by programing language, Matlab. The process of experiment is simplified by standard operating procedure and the safty of facilities is controled by monitor. Based on the improvements above-mentioned, we can develop an more automatical system to save time effectively, better work conditions, reduce personnel cost, and acquire more objective outcomes. We set up experiment in an water tank of dimension 4mx3.5mx2 m, located in National Sun Yat-sen University, and choose a copper sphere of diameter 60 mm as target. The projector and receiver both are iTP-192k transducer with directivity and frequency response at 192k Hz. In order to measure the 2-D scattering field at 1 m from target without strong boundary interference, projector transmits 64 sine waves at 3.8 Hz and receiver changes direction by block and rotating mechanisms. The effects of direct signal in forward scattering field can be reduced by modified signal process according to Ding (JASA, 101(6), pp.3398-3404, 1997). The difference between actual and theoretical magnitude, based on Hickling (JASA, 34(10), pp.1582-1592, 1962), is 2~3 dB in most of backward scattering region and parts of forward scattering region (30¢X~60¢X and 300¢X~330¢X), and 5~10 dB in else forward scttering range. Generally speaking, that experimental result displays symmetrical distribution corresponds with theory and indicates the design of mechanism, software and procedure in this study practicable and useful for further research in the future.

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

As humans seek to explore and exploit underwater environments and resources the need for tools and techniques to assist in this is critical. An important component of working in any environment is understanding dimensional information about that environment. The predominant inspection techniques in an underwater environment are sonar and video systems, However, these do not provide fine detail and often critical geometric measurements about small features and defects. Underwater laser scanners have been investigated for underwater measurements and demonstrated to operate with success; however, the current deployment options of these systems are limited. Through this thesis, an easy to deploy underwater laser scanner was developed, overcoming mechanical integration and sensor calibration challenges not previously dealt with. By integrating the laser, sensor and rotary actuator into a single housing, the calibration of the sensor is successfully maintained through multiple deployments of the scanner into a variety of applications. The developed scanner has been successfully deployed for a variety of applications, from Underwater Archeology and Biology in the Dominican Republic and Antarctica to Offshore and Inland asset inspection in the Gulf of Mexico to the Middle East and the Persian Gulf.

During the underwater vehicle R&D process, a crucial task in the beginning phase is to decide the specifications of sensors and actuators. The designers need to make decisions if an off-the-shelf product will meet the requirement, or more efforts should be devoted to the development of a component. The communication format undertaken between the controller and the subsystems is another important design issue worth of close attention. Once these specifications are settled, it will be very troublesome to change them afterwards in case a design flaw is discovered. It will be even worse if the problems are found after the prototype vehicle is constructed. In order to ensure the flexibility and shorten the development time, this paper proposes an architecture for general-purpose low level controller suitable for underwater vehicles. We suggest using the idea of ¡§tiers¡¨ to construct a vehicle controller with multiple layers. Generally speaking, there are many different paths of information flow in a vehicle control system. It can be high-level tier and abstractive intention of the human operator interpreted by the man-machine interface; or the mid-level tier control commands to maneuver the vehicle to a specific direction; down to the low -level tier as the raw commands fed to the thrusters. The performance and the reliability of the system deeply depend on the flow of these information and commands. High- and mid-level tiers information can be modeled mathematically, but the low-level tier is product-dependent. In other words, once a new sensor or actuator is installed, the control software related to these components need to be revised accordingly. The modification of the software might exist at multiple places if the structure is not organized as tiers. In order to maintain full flexibility of the vehicle controller structure throughout the R&D period, the high- and mid-level will be implemented in the man-machine interface for ROV case, and in the mission planner in the AUV case. The low-level tier is implemented in the onboard computer. The onboard low-level controller covers a variety of communication format of physical ports, such as serial line, D/A, A/D, D/IO and PWM. Port setting parameters, such baud-rate or DA range, can be specified remotely on the surface. The physical connecting ports of the sensors can be changed freely without rewiring or reprogramming. Taking the stability of the controller as the top priority, we used DOS operating system as the platform to implement our concepts. DOS has been in the market for more than two decades, but it has the merits of fast in booting, highly stable, efficient in computation. We use its timer interrupt service INT 0X1C to construct a realtime thread to poll the readiness of sensory channels, and uploads the data to the surface via a channel-driven packet. The packets delivered to the surface are split into channels and reconstructed back to their original raw data format. The other necessary service routines, such as DA, AD and DIO, are also embedded inside this thread for its promptitude. We constructed an experimental platform with this low-level controller to verify if the vehicle alitude control can be accurate enough as the carrier of the Seafloor Laser Scanner developed by our lab. Prior to the experiments, issues, such as whether the bouyancy of the system is pro or con for driving the vechile, were studied with Simulink. The poorness of altitude control caused by the deadzone effect of the thruster failed to be duplicated as in the simulation, while the alitude control gave a tracking error within ¡Ó 5cm.

Underwater operation and sampling has been replaced by ROV (Remotely Operated Vehicle) and underwater manipulator gradually, which can avoid divers to face the dangers due to the environmental pressure and low temperature. When ROV to carry out the mission, the operator sees the undersea environment and the target with the information feedback from the sensors. Recently, we developed a general purpose controller for controlling underwater robotic systems. We plan to install the manipulator on the ROV with the same general purpose controller. One of the concerns in desgining is: the ROV generally mantains neutral buoyant in seawater. When adding or removing any components, the arrangement of balast weight needs to done again to keep the balance of the system. Moreover, the center of gravity will be changed such that dynamics of the ROV will be different when collaborating with the underwater manipulator. To resolve these problems, we review the design and hope to reduce the size and weight of each component.The new design also introduces the use of a junction box. The junction box keeps all the circuits, power converters and motor control card. It allows the reconfiguration of power and commands pathway much easier. To reduces of the size of the housings, the gear transmission set is moved out of the housing. According to the positioning accuray requirement of each axis, a DC servomotor or a DC motor is installed. Underwater manipulators do not require agile motion. Therefore we use a gear-worm set as the transmission between links to increase torque. The motion control is implemented with a Jacobian to calculate the increment joint angles for joint coordinate control. Human-interface was developed with Borland C++ Builder and OpenGL to let the operator to simulate and control of the manipulator with an input of a 3D joystick.

In the development of underwater vehicles, it is necessary to conduct performance test in the water tank. However, different factors need to be considered depending on different cases. The purpose of this paper is to construct a simulation platform in the air to study the scenarios like side current or constant height profiling. Although these tests are difficult to be performed in the water tank, we can get some solutions from observing the dynamics of simulation platform. The simulation platform we used consists of three links to constraint the motion in a polar coordinate system. It carries a wireless micro-camera, and two DC motor-driven propellers. At the end of the distal link and metal disk is attached on the other side of the pivot of the last link to provide counter-weight which can simulate different status of the "buoyancy" of the platform. The encoder which is uses to trace the motion of the simulation platform, is mounted at each join between two links. The control program has two parts: servo control of propellers and target tracking. In order to approach to the real-time searching, we derived image with gray scale instead of color form to increase image refreshing rate during the tracking process. For the current experiment, the target is at dot generated by an LED. The location of the bright dot is detected by a histogram-based threshold, and the actual location is further refined with intensity-weighted algorithm. The offset between of the target and the center of the image is used as the feedback to command the propellers to drive the platform. The goal is to keep the target at the center of the image as close as possible. A linear PD control (proportional - derivative) is implemented to drive the propellers. Preliminary experiments show that the simulation platform can track a target with about 15 frames per second refreshing rate under the condition that the target does not move too fast and vanishes in the image. When ROV with laser scanner syetem, seafloor away from ROV's accuracy is necessary. In this eassay, we use tracking angle and tracking bright dot to qualify and quantify the influence of buoyancy and propeller on the altitude control in different cases.

The fishing method of trawling, or dragging, has long been shown to be harmful to a plethora of sea life inhabiting the world?s oceans and inland waterways. Fishing nets scour the seabed, disturbing everything in their path, while usually in search of only one type of bottom-dwelling species. Impacts to the seafloor include a removal of topographic features, disturbance of the upper sediment layers, including deep furrows, as well as physical and chemical changes to sediment morphology. While biological organisms and communities can potentially recover from this destruction, archaeological data cannot. Fishermen have been raising important artifacts in their nets for over a century. These finds have helped archaeologists locate significant sites, but they also have the adverse effect of irreparably damaging these sites. This thesis explores the impacts of bottom trawling on underwater cultural heritage. The methods and gear used by trawlers and their documented effects upon the sea floor are identified. Examples of the types of damage shipwreck sites receive after being impacted by trawling are presented. Instances where fishermen have raised prehistoric artifacts from inundated land sites are also introduced. The fishing and archaeological communities must cooperate to limit further damage to underwater cultural heritage around the globe.

Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Bourke, Robert H. ; Coppens, Alan B. "September 1990." Description based on title screen as viewed on December 30, 2009. DTIC Identifiers: Raymode model, PE model. Author(s) subject terms: Oceanographic, acoustic survey, East Ionian Sea, PEmodel. Includes bibliographical references (p. 86-88). Also available in print.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 93-95. Also available online.