A nonlinear control approach for trajectory tracking of slender-body axisymmetric underactuated underwater vehicles

This paper develops a novel nonlinear control approach for slender-body underactuated underwater vehicles with a body shape symmetric with respect to the longitudinal axis. Compared to aerial vehicles, added-mass effects are much more preponderant and complex for underwater vehicles, especially for slender bodies. By considering an axisymmetric body, these added-mass effects along with dissipative hydrodynamic force are carefully taken into account via various adaptations and decompositions, resulting in a modified "apparent" force independent of the vehicle's orientation and subsequently a nonlinear system with a triangular control structure. The proposed controller is then complemented with an integral correction term so as to enhance its robustness with respect to model uncertainties and external disturbances. Comparative simulation results conducted on a realistic model of a quasi-axisymmetric underwater vehicle illustrate the performance and robustness of the proposed control approach.