Mario A. Jordán

Nonlinear identification of mooring lines in dynamic operation of floating structures

An adaptive algorithm for on-line estimation of physical coefficients of cables in viscous environment is presented. The procedure is useful for obtaining cable characteristics, which are needed in stability analysis and control system design for moored floating structures. It uses measurements of position and forces from on-board instrumentation. It is also able to track changes in the depth and to test for parameter consistency in order to confer the estimation robustness with respect to dynamic perturbations. It is based on nonlinear solvers, which can cope with transcendental functions of the model structure. The proof of asymptotic convergence is presented. Finally, three basic case studies are analyzed.

A Speed-Gradient Adaptive Control with State/Disturbance Observer for Autonomous Subaquatic Vehicles

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

Guidance of Underwater Vehicles With Cable Tug Perturbations Under Fixed and Adaptive Control Systems

This paper is concerned with the study of guidance of underwater vehicles subject to cable perturbations due to action of currents and harmonic waves. The general case involves a variable cable length that is usually deployed during vehicle tactics. Control situations are considered, namely, trajectory tracking and position regulation when the reference trajectory for the vehicle is given beforehand. To this end, a control system is designed with adaptive features. A great effort is made in this paper for modeling the cable dynamics in a quasi-stationary state. This model can serve the operator to compensate for the perturbation automatically during teleoperation. Moreover, in the adaptive systems, the perturbation is filtered automatically without having to embed the cable model in the controller design. Effects of the cable perturbation on the control system in adaptive and fixed systems are analyzed comparatively. Proofs of convergence to the tracking error to a residual set are given rigorously in the framework of total stability. The features of the controlled behavior are illustrated by numerical simulations in a case study in six degrees of freedom.

Robust Adaptive Predictive Fault-Tolerant Control Linked with Fault Diagnosis System Applied On a Nonlinear Chemical Process

In this paper, a new fault-tolerant control (FTC) strategy is proposed to compensate for the effects of faults and to improve the overall performance for nonlinear stable plants. The FTC approach involves a commutation of a linear time-varying robust filter in the feedback path of the control loop in synchronization with an adaptive predictive controller. The decision of which mode has to work is based on specific conditions accounted in the control algorithm. In addition, the fault-tolerance ability of the controller has been further improved by a fault-diagnosis system (FDS) designed for detecting two fault types: specific bias at the sensor and time delay at the actuator. The FDS is developed by using wavelet decomposition and identification techniques respectively. An implementation on a continuous stirred tank reactor (CSTR) with jacket is presented as a simulation example for analyzing the effectiveness of the FTC linked with FDS methodology proposed here

On the Presence of Nonlinear Oscillations in the Teleoperation of Underwater Vehicles under the Influence of Sea Wave and Current

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.

An approach to improve the performance of adaptive predictive control systems: theory, simulations and experiments

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.

Adaptive Control for Guidance of Underwater Vehicles

Underwater vehicles are extensively employed in the offshore industry, subaquatic scientific investigations and rescue operations. They are sophisticated mechanisms with complex nonlinear dynamics and large lumped perturbations. They can remotely be operated or eventually autonomously navigate along specified scheduled trajectories with geometric and kinematic restrictions for obstacle avoidance or time-optimal operations (Fossen, 1994). In a wide spectrum of applications, underwater vehicles are generally described by nonlinear and time-varying dynamics. For instance, dynamics with variable inertia and buoyancy arriving from sampling missions or hydrodynamics related to large changes of operation velocity or current perturbations in which laminar-to/from-turbulent transitions are involved in the hydrodynamics. Due to the inherent nonlinear equations of motions, perturbed environments and complex missions, subaquatic vehicles require the guidance by means of complex controllers that usually involve automatic speed controls, dynamic positioning and tracking, and autopilot systems for automatic steering of depth and altitude. It is experimentally corroborated that adaptive techniques may provide superior trajectory tracking performance compared with the fixed model-based controllers (Smallwood & Whitcomb, 2003; 2004). Many different adaptive and robust adaptive approaches for underwater vehicles have been discussed in the literature in the past 15 years to handle uncertainties related to the dynamics, hydrodynamics and external disturbances, see for instance Fossen & Fjellstad, 1995; Hsu et al., 2000, Antonelli et al., 2004; Wang & Lee, 2003; Do et al., 2004. However, the employment of novel high-performance nonlinear control design methodologies like backstepping (Krstic et al., 1995), passivity-based approaches (Fradkov et al., 1999) or sliding modes (Hsu et al., 2000) do not appear in the literature except as incipient applications, see for instance, Do & Pan, 2003; Li et al., 2004; Jordan & Bustamante, 2006; 2007; Conte & Serrani, 1999. From previous theoretic results and some experimental corroborations, it seems that novel adaptive techniques can give rise to an improvement of the global performance in path tracking, above all when more precise manoeuvrability with a high celerity in motion is necessary in a changeable and uncertain subaquatic environment. O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg

Oscillation control in teleoperated underwater vehicles subject to cable perturbations

In this paper a control scheme in fixed and adaptive modus for path tracking of ROVs under perturbations of waves and uniform flow is presented. Particularly, the case of systematic sampling missions at constant depth or altitude with variable cable length are focused in the investigation. A model of the cable perturbation is developed in order to embed it in the controller design. The controller is based on speed-gradient laws in adaptive or fixed modes alternatively. The proposed scheme allows the estimation of the cable perturbation based on a model of force, shape and position of the extremes. Simulations show the presence of nonlinear oscillations particularly in the regulation about fixed positions, where chaotic behaviors can be observed. The paper compares the control performance obtained with and without the estimation of the cable perturbation in both the fixed and adaptive controls. The results are illustrated by means of a case study in six degrees of freedom for both path tracking and regulation.

Adaptive robust control using discrete Laguerre functions

This paper presents a new approach to adaptive predictive control systems with robust characteristics based on nonparametric descriptions. The estimator deals with a parsimonious model of a linear stable plant based on discrete Laguerre functions. The model uncertainties are captured by the estimator as time-varying upper and lower bounds for the Laguerre coefficients. Combining the family of uncertain models with predictive control techniques in an adaptive control loop robust stability can be ensured in a Kharitonov hypercube in the space of controller coefficient. Robust stability conditions and convergence properties of the adaptive control system are performed.

A Totally Stable Adaptive Control for Path Tracking of Time-Varying Autonomous Underwater Vehicles

Abstract This paper deals with the problem of adaptive path tracking of autonomous underwater vehicles with time-varying dynamics. The controller design is based on a speed-gradient adaptive law. A high-performance control behavior is aimed, so the full actuator dynamics is considered together with that of the vehicle. To this end, a state/disturbance observer is developed in the state feedback employing inverse dynamics. It is proved that the error paths can converge asymptotically to null when only the nonlinear static characteristic of the thrusters is involved in the design. When the actuator dynamics is considered too, only attractivity of the error paths to a residual set can be stated. The framework for this last proof relies on the concept of total stability. One main characteristic of our approach is that it can cope with a wide variety of bounded time-varying parameters with no limitations at all on their rates or a-priori knowledge.