The approach of improving the roll control of a slocum autonomous underwater glider

Zhou, Mingxi (2012) The approach of improving the roll control of a slocum autonomous underwater glider. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (30MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Currently, Slocum Autonomous Underwater Gliders (AUGs) are widely used in oceanographic research. However, compared to the other legacy AUGs, Spray gliders and Seagliders, the roll controllability is insufficient on the Slocum gliders. This thesis discusses two different approaches of improving the roll controllability on a Slocum underwater glider. With improved roll motion, the Slocum glider has the potential to be involved in iceberg management along the Newfoundland and Labrador coast, and to fulfill the mission of iceberg surveillance and data reporting; for example, iceberg draft measurement and profiling. The operation of a Slocum glider will be safer and less expensive than the current ship based method. A simplified dynamic model of an underwater glider is derived and evaluated by comparing the simulation result with the field trial data collected in Conception Bay, Newfoundland and Labrador, Canada, 2010. The presented dynamic model can be easily modified to represent various realistic Slocum glider internal mass arrangements or even other types of Autonomous Underwater Vehicles (AUVs). In addition to the existing internal structure of a Slocum glider, a movable mass, the position of which is variable in the wingspan direction, is introduced to investigate the 6 degree of freedom (DOF) performance of a Slocum glider, especially the roll and yaw motions. Two roll control mechanisms are introduced in this thesis. Based on the field data, a small roll angle (2° to 5ﾟ)exists in the mission due to a small error of separation between the center of buoyancy and the center of gravity in the roll trimming or other environmental effects. An Autonomous Roll Trimming Mechanism (ARTM) evolving from the wingspan movable mass is designed to simplify the roll trimming process and to eliminate the dynamic roll angle error during the flight. In the design of the Deflectable Wingtip Mechanism(DWM), the standard flat-plate wing sets are replaced by NACA00l2 airfoil sections and deflectable wingtips. A miniature geared stepper motor is integrated into the wing to control the wingtip deflection angle. The mechanism rolls the glider by reversing the lift forces on the wingtips which create a rolling moment and roll the Slocum glider with an angle up to 45°. Simulated with the previously introduced and evaluated dynamic model, the Slocum glider flies in a spiral motion with a fixed roll angle with a deflection on the wingtip. In order to control the spiral motion properly, the spiral parameters, such as turning radius and roll angle, are further examined. We illustrated the relationship between the angle of attack of the wingtip and the spiral motion performance. -- Beyond the mathematical analysis of the DWM, a hydrodynamic test is applied on the DWM. A hydrodynamic testing platform is designed, on which the angle of attack of the DWM, the sweep angle, and the wingtip deflection angle are variable. The experiments are conducted in the Open water flume tank located at the Engineering Department of Memorial University of Newfoundland. The forces and torques are collected using a 3-axis JR3 load cell. As a result, the hydrodynamic characteristics of the DWM with different experimental settups are Obtained and compared.

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