| Ship rolling has great impact on the safety and comfort of navigation. Fin stabilizer as an active roll damping device, with its excellent anti-rolling effect, is widely installed in various types of ships. For the insensitive to disturbance and system parameters change, sliding mode variable structure control can be employed to improve the anti-rolling effect of fin stabilizer in different sea conditions, and its design process is simple. Based on this, sliding mode variable structure control incorporated with fuzzy control is designed for fin stabilizer in this thesis. The main research contents in this thesis are as follows:(1) Based on the theory of wave spectrum analysis, crested random wave disturbance model is built, wave height and wave slope angle of different sea conditions is simulated using equal energy interval discrete method.(2) Considering the nonlinear factors in the roll motion when sea condition is heavy, the nonlinear ship rolling model is built according to the ship parameters of a frigate.(3) Based on the principle of sliding mode control, a sliding mode controller is designed for the fin stabilizer system. The simulation results show that fin stabilizer sliding mode control can effectively reduce the ship roll angle, and high anti-rolling efficiency is maintained when sea condition is severer, which verify the controller has strong robustness.(4) The upper bound value of interference and uncertainty need to be estimated in the design process of sliding mode controller, which increases the difficulty of the design process. To solve this problem, fuzzy control is adopted to adjust the control switching gain.(5) In order to overcome the chattering of classical sliding mode control, fuzzy tuning is used to adjust the switching item which cause chattering phenomenon in the classical sliding mode control. Simulation results show that this method can effectively weaken the chattering of control signal, and good anti-rolling effect can be obtained. |
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