In this paper the design of a nonlinear adaptive control system for fully actuated autonomous underwater vehicles in 6 degrees of freedom is presented. Both the positioning and kinematic tracking-problem are dealt with jointly in the adaptive approach. No knowledge about parameters of the vehicle dynamics and hydrodynamics is required beforehand for the design, except only for the thruster dynamics. The adaptation was carried out through a nonlinear speed-gradient adaptive control law. The dynamics of thrusters is considered in the design employing an inverse-dynamics technique and state/disturbance observation. The proof of the asymptotic convergence of the overall controlled system is shown. Selected numerical simulations depict the features of the proposed approach

In this paper an approach to improve the overall performance of indirect adaptive control systems tailored for non-linear stable plants is presented. The approach involves a commutation of a linear time-varying robustness filter in the feedback path of the control loop in synchronization with an adaptive controller. The algorithm is framed in the celebrated IMC structure for predictive control systems. It can automatically suit to structural changes in the system as order and dead-time, and can deal with plants with zero dynamics. The convergence and stability of the system is analysed in details. It is shown through numeric simulations and experimentation on a heat exchanger with cooling system, that undesired transients due to abrupt and significative changes in the dynamics can be efficiently damped down by the developed control algorithm, achieving a high-quality performance in steady state.

The contribution of this paper is the study of nonlinear oscillations of remotely operated vehicles (ROVs) subject to strong currents and harmonic waves when the vehicle is servocontrolled around a fixed position. A complete model for quasi-stationary dynamics of a ship-cable-ROV system was developed. A high-performance control system was designed, in which the cable force is calculated on the basis of measured end positions. Our analysis reveals that the ROV behavior can transit from period one to chaos without the thrusts enter saturation zones. This feature appears more marked as long as the cable stiffness increases. In view of recent results, one can broadly say that the cable elasticity acts as a suppressor of the complete subspectrum of subharmonics in the vehicle dynamics, and simultaneously, as an effective attenuator of its superharmonics.