Enhancing the dynamics of an oceanic AUV by a Coupled-Fins-Propulsors roll control system

Abstract

Autonomous Underwater Vehicles (AUVs) are exposed to several internal or external forces or moments causing roll instabilities. The coupled nonlinear dynamics of an AUV requires designing and utilizing an appropriate roll control system to operate well in various missions. In this paper, the roll dynamics and control enhancement of a REMUS AUV is studied using a Coupled-Fins-Propulsors (CFP) system by developing a six-degrees-of-freedom (6DOF) simulator. The results show that: 1) The roll angle deflections usually have adverse effects on coupled dynamics of the AUV in both open-loop and closed-loop systems; 2) In large roll angle deflections, the CFP system show a proper selection of 30% CRP (contra-rotating-propellers) and 70% FDF (Four-Decoupled-Fins) (49% SF (Stern Fins) and 31% RF (Rudder Fins)) can better control the roll dynamics by reducing the oscillations. 3) For φd < 18°, the FDF, CRP, and CFP, for 18°<φd < 60°, the FDF and CFP, and for 60°<φd < 70°, the CFP system could produce the adequate roll control forces and moments. 4) A limited desired roll angle can be achieved at a given forward speed; the maximum value is φd = 70 for ud > 4 m/s.