Ship Anti-rolling Control Strategy At Low Speed

The fin stabilizer reduces the ship rolling by means of active torque countermeasure.Since the lift depends on the incoming flow velocity,the fin stabilizer using traditional control method has no anti-rolling effect at zero or low speed.In order to achieve full speed anti-rolling function of the fin stabilizer,it is necessary to improve the control strategy,fin profile and execution structure.This paper studies the corresponding control strategies for the zero speed and low speed of ships and aims to achieve full speed anti-rolling for a certain type of ship.The appropriate control strategy is selected by constructing simulation model.The performance is verified by simulation and ship model test.This paper analyses and compares the technical development of the full speed anti-rolling device at home and abroad,and sorts out the research methods of the fin stabilizer control strategy.Firstly,the ship roll motion simulation model is established,which mainly includes the model of ship rolling,fin stabilizer servo system,roll detection sensor and fin stabilizer.In the model,the force on the fin at different ship speeds and the mechanism of generating stability torque are analyzed.Then,the appropriate control strategy is selected for the zero and low speed condition of the ship.Aiming at the zero speed condition,PID control algorithm is adopted to design the controller.Since PID parameters are designed for specific sea conditions,the control effect is not ideal at violent sea conditions.In order to solve this problem,the control strategy is designed based on the model of fin lift without incoming flow and the prediction algorithm of wavelet neural network.The ship rolling simulation experiment under irregular waves is carried out to obtain a series of ship rolling period,and as the training sample of neural network.After off-line training of sample data under a large number of working conditions,the weighting matrix of the neural network is assigned.From this,the neural network predictive controller is obtained by collecting roll detection sensors and predicting the roll motion trend.The system model is built in Matlab/Simulink and the results show that the predictive control algorithm can effectively reduce the ship roll motion at zero speed,which proves that the algorithm is effective.In order to effectively utilize the lift of the fin at low speed,a constrained predictive control method for low speed is proposed.Considering the stall angle of fin stabilizer and the mechanical limitation of actuator,the cost function is selected according to the actual system.A low speed fin stabilizer controller is designed by using the constraint model predictive control algorithm.In the simulation environment,a controller model is added,and the results show that the fin stabilizer controlled by the constraint model can effectively reduce the ship rolling motion at low speed,which verifies the effectiveness of the algorithm in the fin stabilizer control mode at low speed.Finally,the software and hardware of ship model and fin stabilizer control are designed on the basis of three similarity criteria for a scientific research ship.The basin test is carried out in the tank,and the experimental data and theoretical simulation data are analyzed and compared.The results show that the control strategy selected and designed at zero speed and low speed are applicable and have ideal anti-rolling effect.