Fuzzy Iterative Sliding Mode Control For Sail-Assisted Ship Motion

With the advent of oil crisis and the enhancement of the environmental awareness, the sail-assisted ship gradually attracts people’s attention because of the energy-saving feature. It has become one of the hotspots of shipbuilding industry in research of saving energy and protecting the environment with the wind which provides the ship forward auxiliary thrust. This paper mainly focuses on the study of the modeling and motion controller of the sail-assisted ship.Firstly, for sail-assisted ship, based on MMG separation model, a four degrees of freedom sail-assisted ship motion model is established, which includes the marine diesel engine characteristics. Obtain the sail force functions in best attack angle through the analysis of the sail force in complex environment. Then, with the obtained functions and the circular-arc sail, the four degrees of freedom sail-assisted ship motion model for the 76000 DWT bulk carriers of large ocean-going’Wen Zhuhai’is constructed, and the simulation of the model has been carried out using software Matlab/Simulink.Secondly, for the uncertainty nonlinear sail-assisted ship motion model influenced by the wind and current, a fuzzy iterative sliding mode course controller is presented. The proposed controller uses nonlinear hyperbolic tangent function to design the system output sliding mode. The strict boundedness characteristic of the hyperbolic tangent function can help the system avoid the estimating of the uncertain parameters and disturbances. To optimize the parameters and enforce the adaptive property of the controller, binding with the fuzzy adaptive theory, the sliding mode parameters are optimized by the fuzzy system. Then we define a chattering variable and an adaptive heuristic critic function to adjust the control fuzzy system’s structure parameters on-line, which can achieve good performance in restraining the controller output chattering.Thirdly, for the lateral drift which is caused by the sail and the current will ultimately cause the route deviation, aiming to improve the path tracking performance, reduce the number of ship steering and the power, basing on the nonlinear iterative sliding mode controller, fuzzy parameter optimization system and the adaptive heuristic critic algorithm, a fuzzy iterative sliding mode controller based on adaptive heuristic critic algorithm is designed for the sail-assisted ship straight line path control.Finally, carrying out the sail-assisted ship’s heading and the track control simulation with the software Matlab/Simulink, the results reflect that the controller is robust against the perturbation from the uncertain parameters and disturbances, and can also achieve good performance in restraining the controller output chattering.