Identification of a simplified AUV pitch axis model for control design: Theory and experiments

This paper presents an system identification algorithm for the longitudinal motion of a streamlined, tail-controlled, miniature autonomous underwater vehicle (AUV). The motion of a rigid body in six degrees of freedom is restricted to the dive plane to derive a fourth order dynamic pitch axis model. Based on the mechanical design of the vehicle, we impose symmetry and buoyancy assumptions that allow further model truncation. Basic dependencies between inherent stability of these truncated models and system parameters such as hydrodynamic coefficients are addressed. For the goal to rapidly design an AUV attitude control system, we experimentally show that it is sufficient to consider a second order dynamic model. We identify model parameters by matching the input and output behavior via least squares. Data collected during field trials validates both the system identification and the utility of a second order model for control design.