With 900 Autonomous Underwater Vehicles (AUVs) required over the next decade (Newman et al., 2007) existing survey-style AUVs need improved utilization factors. Additional control devices to extend operational capability need consideration together with the interchange between AUV control approaches. This paper considers supplementary through-body tunnel thruster control during the transition from survey operation to low-speed manoeuvring. Modified manoeuvring equations permit investigation of energy level demands as a positively buoyant AUV is slowed down from cruising speed to maintaining a stationary position. A suitable model of the selected thruster device is proposed following a literature review of tunnel thruster performance.
SUMMARYPositively buoyant autonomous underwater vehicles (AUVs) operate at survey speeds with a pitch angle that is maintained through application of the control surfaces, sufficient to generate hydrodynamic forces to counteract the excess buoyancy. To facilitate lower forward speeds and the ability to hover requires some additional method of control. This paper reviews possible options and then indicates how control can be achieved using a single or pair of through-body tunnel thrusters. New equations appropriate to AUVs are proposed and experimental results are used to estimate the equation parameters. These equations are used within a simulation of the Autosub AUV to determine the response of the AUV during the transition between survey and low speed operation. The results obtained from the simulations are analysed in terms of the performance of the AUV and the demanded energy levels to assess the feasibility of using tunnel thrusters as a low speed control device.
NOMENCLATURE
The University of Southampton's entry into the Student Autonomous Underwater Challenge -Europe (SAUC-E)2007 was a custom designed and built autonomous underwater vehicle (AUVj named SotonAW'. Originally developed for SAUC-E 2006, the vehicle was significantly upgraded for the 2007 cornpet~tion. The mechanical design of the vehicle is describ4, and an overview of the autonomy and control approaches employed is provided. The updated vehicle successfully competed in SAUC-E 2007, winning first place in the overall competition and taking the BAE Systems prize for innovation in autonomy.
Autonomous underwater vehicles are a developing technology capable of undertaking a wide variety of different tasks. The development of these vehicles is aided by the use of simulations of their performance. These simulations require accurate modelling of the propulsion and control devices employed to calculate the response of a vehicle to different situations and control strategies. Simulations of underwater vehicles tend to include models of the dynamic performance of the thrusters employed, however, the simulations neglect some of the hydrodynamic interaction effects. These interaction effects include thruster–hull and thruster–thruster interactions similar to those encountered on dynamic positioning surface vessels. This paper assesses these effects for autonomous underwater vehicles and, where appropriate, suggests models for use in simulations.
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