Development and testing of a functional model scale underwater glider for research in dynamics and control

Abstract

Due to their long endurance and low operational cost, underwater gliders are a proven technology for collecting data from the oceans. The AUV groups at NRC-OCRE (National Research Council Canada, Ocean, Coastal and River Engineering) and MUNAOSL (Memorial University of Newfoundland - Autonomous Ocean Systems Lab) are designing, building and testing the 'lOT Glider'. It is a test-platform prototype for the development of low-energy-budget gliders for long-duration missions, and has been designed for performing sawtooth-like trajectories in a tow tank which is 7m deep and 200 m long. The lOT Glider has an overall length of 1.56 m, a hull diameter of 115 mm and a mass of 9.6 kg. This glider is therefore a multi-function vehicle for concept design, assessment of hydrodynamic performance and control systems research. It also provides comprehensive, multi-feature capabilities which are inexpensive to implement, test and verify. -- The current IOT Glider has a complete buoyancy engine, an active pitch and roll control mechanism, and, attitude and pressure sensors. The buoyancy engine uses a linear actuator and a D-type diaphragm to change the glider's buoyancy. The pitch and roll mechanism provides independent control of the longitudinal and rotational positions of the 470 gram battery pack, and provides the desired pitch angle and turning rate. This glider has a pair of swept wings which can be adjusted fore-and aft, a hollow nose section and a hollow tail section made from ABS plastic via a rapid prototyping machine; these sections can be used for additional sensors, and for ballasting and adjusting trim conditions. -- For prediction purposes, a MATLAB-based motion simulator has been developed for mission planning. The six-degree-of-freedom motion equations include the effects of added mass, hydrodynamic forces and moments, and hydrodynamic damping. Several strategies are used to improve the quality of these predictions, including CFD (Computational Fluid Dynamics) analysis, analytical methods and empirical techniques.