Abstract
This paper aims to develop a genetic algorithm to adjust an fuzzy controller for Vessels’ Dynamic Positioning System (Vessels’ DPs). It is well-known that nonlinearities affecting the control accuracy of the DPs are related to the arrangement of different types of thrusters in the vessels, such as azimuth thrusters (electric, L-drive, and Z-drive), bow thrusters, stern thrusters, water jets, and propulsion propellers with rudders. Compared with the traditional fuzzy control methods, the proposed Robust Adaptive Fuzzy Control using Genetic Algorithm (RAFC-GA) not only overcomes the influence of nonlinearities in the DPs, but also eliminates the impact of parameter uncertainties. Therefore, the tracking performance is excellent and robustness is maintained. The RAFC-GA control method is superior to the conventional fuzzy control methods in the two following aspects: 1) to find the optimal values for the fuzzy structure parameters to satisfy the robust condition under the effect of disturbances and nonlinearities in the DPs without weakening the output tracking performance and robustness, 2) to improve the quality of the system by optimizing values for the fuzzy structure using genetic algorithm which dynamically adjusted the coverage domain width and the overlap degree of membership functions. Simulation results of the RAFC-GA are evaluated in comparison with other methods. The RAFC-GA performs the desired transient response of DPs better than others in three case studies, which proves the effectiveness of the proposed solution.
Highlights
To overcome the aforementioned problems, we propose the RAFC-Genetic Algorithm (GA) for Vessel’s dynamic positioning system (DPs)
The contributions of the paper are presented as follows: 1. We propose the model of adaptive fuzzy control for vessel’s DPs to overcome the effect of three main factor that are uncertain parameters of system, dynamic and environment disturbance, and dead-zone inputs and time-delay are considered to be the two main factors causing nonlinearity of DPs
We aim to propose the RAFC-GA controller design for the DPs which expressed in equation (1) and equation (2)
Summary
O VER the past few decades, there are some methods utilized to keep vessels’ position in the sea, namely the use of an anchor spread, the use of a jack-up barge and dynamic positioning system (DPs). Even though each method has its own advantages, dynamic positioning (DP) has many more operations possible that were not feasible before. It is easy for the vessels to change position using DPs thanks to its excellent maneuverability. DPs requires no anchor handling tugs, does not depend on water depth and are not limited by obstructed seabed. DPs is primarily concerned with the vessels’ control in the horizontal plane including surge, sway and yaw. The control system of DPs plays an important role in improving the efficiency of the vessel in most sea conditions
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