Hydrodynamic Data for Manoeuvring and Control of an AUV Determined by Tank Tests and Free-Sailing Trials

Autonomous Underwater Vehicles (AUV's) can be used for a large number of subsea acitivities in different modes of operation varying from the ROV-mode with on-line control and power supply from the surface, to the true AUV-mode where the vehicle performs its pre-programmed tasks with full autonomy.For any mode of operation a complete set of hydrodynamic data will be required for the optimum design of the steering and manoeuvring equipment and strategies. Precise track-keeping and fast obstacle avoidance are important qualities of an underwater vehicle. The data necessary to investigate these properties and to program the control systemm comprise added mass and inertia coefficients, damping, lift and drag coefficients of the vehicle and its control surfaces, as well as resistance and propulsion characteristics. Only few hydrodynamic data for AUVs have yet been published, so dedicated tests and calculations will usually have to be carried out for each new vehicle.The experimental methods applied to obtain a complete set of hydrodynamic data of the flatfish type AUVs "MARIUS" and "MARTIN" are presented. The hydrodynamic data have been determined by tests on the full-scale vehicles, using the towing tank at the Danish Maritime Institute (DMI) which is equipped with a Planar Motion Mechanicsm (PMM). The test data have been used in a dedicated simulation program, intended for the development of the control system and autopilot. The simulation program has been applied to simulate a series of standard manoeuvres, such as turning circles and zigzag tests. Similar free-sailing manoeuvrability trials are described and compared to the simulations. The free-sailing manoeuvres were monitored by the Differential Global Positioning System (DGPS).