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SUMMARYThis paper presents the application of a sliding mode control technique to the dynamic positioning of a turret moored FPSO. The proposed controller is robust with respect to modelling errors and variations in the intensity and direction of environmental forces. Since the system is strongly non-linear, the sliding mode methodology is appropriate because it does not require linearization and uses the complete model for the controller design. Furthermore, the design of the controller term that guarantees robustness is very simple, and can be generalized to any adopted model of dynamic and environmental forces. The main drawback of the sliding controller, related to the high oscillatory control action, is avoided by the de"nition of a &&boundary layer'' near the sliding surface. The controller was tested through numerical simulations of a moored VLCC under several environmental conditions, con"rming the stability and performance robustness.

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This paper deals with the generation of sufficiently smooth position, velocity, and acceleration references for guiding the motion of an ROV along purposefully defined curvature-continuous paths in automated missions. The references are meant to be employed in high-performance trajectory tracking and dynamic positioning applications. The path planning problem is not in the scope of this work. A reference model that synthesises references concerning a single Degree-of-Freedom (DoF) motion is initially described. Then, the use of the synthesised references as the parametrisation for other references concerning multiple DoF motion along curvature-continuous paths is exploited. Results from computer simulations and full-scale sea trials, both based on the NTNU's ROV Minerva, are presented and discussed.Keywords: Guidance system, Path generation, Reference model, ROV, Trajectory tracking. List of acronyms and abbreviations

This paper proposes a MCS (Motion Control System) with trajectory tracking capability for observation class ROVs (Remotely Operated Vehicle) used to carry out automated high-resolution image capturing missions, e.g. inspections, mappings, and surveys. The trajectory tracking capability is a key feature to enable the end users of the ROV technology to acquire sequential high-quality images at proper pace to construct consistent representations of the objects or of the environments of interest. Four degrees-of-freedom are controlled -surge, sway, heave, and yaw. The MCS consists of an output feedback control system that is composed of a high-gain state observer and a MIMO (Multiple-Input-Multiple-Output) PID (ProportionalIntegral-Derivative) controller, that works aided by reference feedforward. Plant linearisation is performed aiming at improving the tracking performance. Stability and satisfactory performance of suitable and smooth reference trajectories are attained despite the presence of unmodelled dynamics, plant parameter variations, measurement noise, and environmental disturbances. Simulated results based on the model of the NTNU's ROV Minerva are presented.

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This paper presents the synthesis of a research on dynamic positioning systems (DPS) for semisubmersible platforms, that included both analytic-computational and experimental parts. Firstly it is presented an overview of the mathematical models used for simulation of the vehicle motion in the horizontal plane. The theoretical treatment of the control problem and its implementation Is also focused. Two different schemes were used to get the controller, one of them is fully original in DPS applications. After that, the control system prototype construction is briefly presented. The evaluation of the control system performance may be done by the analysis of computer simulation and experimental trial results. The trials were carried out in the towing tank of Berlin Technical University, using a propelled aluminium model of a semlsubmersible platform equiped with the I control system prototype developed by the authors.