Design of a robust autonomous surface craft for deployment in harsh ocean environment

Li, Zhi (2013) Design of a robust autonomous surface craft for deployment in harsh ocean environment. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Autonomous Surface Craft (ASC) features fast development in the past few years; however, among publications about ASCs, few discussions are about ASC robustness and especially the reliable operation of the ASC in the harsh ocean environment. Therefore, in this thesis project, a robust ASC that is mainly used for reliable operation in the harsh ocean environment offshore Newfoundland is designed. As the first ASC prototype developed in the Autonomous Ocean Systems Laboratory (AOSL), the main concentration is on reliable ASC electrical and communication system design and the ASC system testing and modelling. -- The ASC on-board communication and control system implements the Controller Area Network (CAN) protocol. External communication with the dock-side computer is built on 900 MHz wireless modems. Four CAN modules are developed to work on the on-board communication network, and many off-the-shelf electrical components were chosen to build the electrical system, which include the Global Positioning System (GPS), Attitude and Heading Reference System (AHRS), Weather Station (WS) and the mbed™ microcontroller. Time synchronization of separate CAN modules inside this CA network is addressed using the presented time reference message (TRM) based synchronization mechanism, and the achieved characteristics are validated using a DPO4034 oscilloscope. The wireless communication link plays an important role in ASC testing, and it can be used to transmit the supervisory command and ASC sensor data between the ASC and the dock-side computer. To support this feature, a Matlab based Graphic User Interface (GUI) is designed to work on the dock computer as the control terminal and the display monitor of the ASC status data. A hand controller is integrated into this GUI for intuitive control of the vehicle, and the ASC position can be shown in quasi-real-time in Google Earth software. -- A hydrodynamic 3 Degrees of Freedom (DOF) nonlinear model for describing the motion of the ASC is generated. Two methods, including the Taylor series expansion method and the system identification (SI) method, are used for model linearization. The designed ASC system was validated by some initial tests, and following t hat, the tow tank tests were performed to determine the vehicle hull resistance and self-propulsion points. Based on the tow tank test data, a propulsion system model was built, and these results were validated by sea trials performed in Holyrood, Conception Bay South, NL. Using the sea trials' data, a state-space steering model for the ASC was identified based on the SI method.

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