Preliminary experiments in comparative experimental identification of six degree-of-freedom coupled dynamic plant models for underwater robot vehicles

This paper addresses the modeling and experimental identification of six degree-of-freedom (6-DOF) coupled nonlinear second order plant models for low-speed, fully-actuated, and neutrally buoyant open-frame underwater vehicles. We report a comparative experimental evaluation of six different candidate plant models whose unknown plant parameters are estimated from data obtained in free-motion vehicle trials. We report an experimental evaluation of the performance of each of the six different 6-DOF coupled non-linear finite-dimensional plant models for underwater vehicles estimated by total least squares (TLS) by comparing the mean absolute error between the experimentally observed vehicle velocities and the velocities obtained by a numerical simulation of the experimentally identified plant models. We also report a cross-validation which evaluates the ability of a plant model to accurately reproduce observed plant velocities for experimental trials differing from the trial from which the plant model parameters were estimated. We conclude that plant models including fully parametrized coupled quadratic drag terms perform best overall in cross-validation. This study has the following contributions: It is the first reported experimental 6-DOF fully-coupled plant model identification and cross-validation of low-speed, fully-actuated, and neutrally buoyant underwater vehicles; it is the first experimental 6-DOF plant model identification for this class of underwater vehicles during free-flight experiments; and it is the first reported use of TLS to perform 6-DOF experimental plant model identification of an underwater vehicle.