Nonlinear formation-keeping and mooring control of multiple autonomous underwater vehicles

This paper deals with the nonlinear formation-keeping and mooring control of multiple autonomous underwater vehicles (AUVs) in chained form. The AUV formation under consideration is constrained by the desired separations and orientations of follower AUVs with respect to a time-varying leader AUV. First, a time-varying, smooth feedback control law for the formation-keeping of multiple nonholonomic AUVs is presented by taking advantage of the Lyapunov direct method. Its asymptotical convergence to a desired formation trajectory prescribed by a leader-follower pair is guaranteed. Second, a time-varying, smooth feedback control law with asymptotic stability is designed to collaboratively moor the follower AUV to its desired docking position and orientation with respect to the leader by using the integrator backstepping method. Third, the realization problems of physical AUV system and singularity avoidance are investigated for applying the aforementioned control laws to a real formation system of AUVs. Finally, simulation results are provided to illustrate the effectiveness of the proposed control laws.