Oceanographic submersibles--Computer simulation

This thesis describes the development of the hardware-in-the-loop simulation for FAU Autonomous Underwater Vehicles. The development was based on the existing simulation platform. For more efficiency and flexibility, this simulation package was ported to Linux. The hardware-in-the-loop simulation enables developers to connect the vehicle directly to a remote simulator. This kind of simulation is used to test the actual software components embedded in the vehicle system. The simulation package was enhanced by the addition of a 3D viewer. This thesis describes the whole development process, from feasibility study and implementation to qualification phases. This viewer is platform independent and designed to be connected to the simulator. It renders the AUV moving in a virtual environment. This tool can be used during all development steps, from tuning phases to post-mission analysis.

This thesis describes the development of a simulation environment for Autonomous Underwater Vehicles (AUVs) on UNIX platforms. AUV missions can therefore be carried out without going to the sea. The Yoyo controller, a component for AUVs is also described in this thesis. The main function of Yoyo is to control the vertical profile of an AUV while it is navigating underwater performing data collection missions. The development of the controller is done in the simulation environment. Several test cases have been performed, and the test results have clearly demonstrated the successful development of the controller.

Underwater systems behavior prediction has become an important success factor in the design and implementation of marine systems. Most marine systems involve cables for mooring, deployment, recovery, or towing; however, estimating the response of these systems is difficult because of their non-linear behavior. Thus, numerical models are used to simulate submerged cabled systems. At FAU, many mission specific cable simulations have been developed, but no single, all encompassing software package exists. This thesis develops a Windows(c) based software package to quickly and easily create FEA models of underwater cabled systems and simulate their response. The model is based on a discrete finite element analysis using linear elements. The software provides fully integrated and interactive Graphical User Interfaces with a 3-dimensional graphical display of the model, and integrates adapted data analysis and visualization tools. The software provides an easy and efficient way to simulate an underwater system involving cables.

This thesis addresses the problem of tracking a thermocline---a layer of water showing an intense vertical temperature gradient---with an Autonomous Underwater Vehicle (AUV). One of Florida Atlantic University's Ocean Explorer (OEX) AUV has been upgraded, as part of the work described here, by integration of a standard and convenient software interface, and used in several thermocline survey experiments aimed at gathering oceanographic data relevant to thermoclines. A tool that simulates the longitudinal motion of the OEX through a water slice, whose temperature map is read using a simulated temperature and depth sensor, has been developed. Using this tool and information from at-sea experiments, several control methods for the OEX to track a thermocline were analyzed. In particular, two different algorithms were implemented and tested by simulation. Overall, two control algorithms have been validated, and it will soon be possible to provide the AUV with a thermocline tracking capability.

Some Autonomous Underwater Vehicles have recently been designed to mimic the locomotion of underwater animals. A new way of propulsion which uses Oscillating Fin Thrusters (OFTs) has been implemented on the AUV Morpheus, with the Nektor module. In particular, first a low level adaptive controller has been developed with the purpose of studying the characteristics of the OFT. Then, a new vehicle using Morpheus' base has been built in order to implement this module and test it. This required for the Lonworks network to be interfaced with QNXnet to create a multi communication protocol vehicle. Concerning the high level control, some proportional controllers and a 6-degree of freedom adaptive controller have been implemented and tested on the new vehicle. The results from these tests have shown that the Nektor module is suitable for the Morpheus, providing high-maneuverability features unavailable when using more standard propulsion systems.

This report highlights important aspects of previous work with the Ocean Explorer (OEX) autonomous underwater vehicle (AUV) docking system as a background. This includes short baseline navigation, the Tracking Controller, Mechanical aspects of the dock, and results of testing of the docking system for the OEX Details of the Morpheus AUV are then given along with the major concerns faced in trying to adapt the OEX dock to the Morpheus. Using computer simulation, the reaction of the Morpheus when it impacts the dock is explored and the results of at sea testing (the collision of the vehicle and the dock) is discussed. A stinger strength analysis of the docking components is included and finally, suggestions for future work including modifications of the existing dock as well as another docking scheme are presented.

This thesis describes the implementation of a commercially available forward looking sonar (FLS) in an autonomous underwater vehicle (AUV) modified for the task of reactive obstacle detection. Any obstacle lying in the vehicle's path is a potential mission-terminating threat. Inclusion of a forward looking sensor would provide valuable information to the AUV. Threat assessment and navigation would use this information in order to avoid obstacles. The system used for this project is an 8-element transducer FLS at 200 kHz. The sonar control software is done in DOS on a dedicated personal computer in a PC/104 form factor. A variable cell-size grid occupancy search method is used to detect objects in the vehicle path. This thesis describes how this sonar is used for the obstacle detection task (software), how it is integrated (hardware and network) in the AUV and what are the results obtained with the system.

This thesis describes a new Inertial Navigation System (INS), designed for use on the latest generation of Autonomous Underwater Vehicle (AUV), the Morpheus AUVs, developed by the Department of Ocean Engineering. The INS makes use of a high precision Inertial Measurement Unit (IMU) along with a Doppler Velocity Log (DVL), a GPS/DGPS system and a flux gate magnetic compass to estimate the position of the vehicle during a mission. Extensive data processing methods are used in order to reduce the sources of error most critical to the navigation estimation. Accelerometers and gyroscopes are used to estimate the vehicle attitude in a complementary filter; a standard Kalman filter performs yaw rate bias estimation, whereas a second, extended Kalman filter, provides position estimation of the vehicle in real time, while also correcting for heading errors. Overall the INS is capable of providing the Morpheus with 1% navigation accuracy over an hour.