Research On Cooperative Control System Of Marine Fin Stabilizer Considering Real-time Obstacle Avoidance

Due to the complex and changeable marine environment,ship navigation is easy to be disturbed,resulting in violent multi degree of freedom motion,in which roll motion poses the greatest threat to the ship.The application of fin stabilizer greatly reduces the roll of the ship.However,when encountering complex marine obstacle field,not only the roll reduction,but also the obstacle avoidance of the fin body should be considered,so as to avoid the damage of the fin,resulting in the decline of the roll reduction efficiency of the system or even the complete loss of function.Therefore,how to realize the real-time obstacle avoidance of fin stabilizer on the premise of meeting the system roll reduction has become an urgent difficulty to be solved,and the cooperative control between fin stabilizer is the key to give full play to the ship’s navigation ability and improve the roll reduction efficiency of the system.According to the law of wave formation,kinematic law and hydrodynamics,the generalized wave disturbance model and ship roll model are analyzed,and the anti roll mechanism and system characteristics are analyzed.On this basis,a realtime obstacle avoidance method for marine fin stabilizer is proposed,which transforms the complex collision problem between fin and obstacle into a simple and easy to solve fin angle constraint problem.According to the shape characteristics of fin stabilizer and obstacle,the fin cuboid equivalent model and obstacle equivalent ball model are established.The main view analysis diagram of real-time obstacle avoidance of fin stabilizer is extracted to solve the change of fin angle during obstacle avoidance.The safe motion area of fin body is planned to add new fin angle constraints.Then,an obstacle avoidance control strategy based on adaptive RBF neural network is proposed to solve the problem of lack of obstacle avoidance in the traditional fin stabilizer control system.On the basis of adding new fin angle constraints,RBF neural network is used to approximate the nonlinear terms of ship recovery torque and damping torque.The network weights are adjusted and optimized online by adaptive control,and the sliding mode control is added to improve the anti disturbance performance of the system.Using Lyapunov stability criterion,Lyapunov function is constructed to prove the stability of fin stabilizer closed-loop control system.The simulation block diagram of the control system is built by Simulink to verify the effectiveness of the fin stabilizer obstacle avoidance control strategy.Finally,a modified calculation method of fin stabilizer lift coupling coefficient considering the influence of tail vortex is proposed to overcome the difficulty of accurate calculation of rear fin lift under the interference of front fin tail vortex.The hydrodynamic characteristics of fin stabilizer are analyzed and the velocity coordinate system is established.The existing effective fin angle calculation method is amended and the rear fin lift calculation formula is optimized.In addition,for the original fin stabilizer obstacle avoidance control system,the effective fin angle of rear fin loss is compensated by feedforward feedback control.The fin stabilizer cooperative obstacle avoidance controller under the influence of wake vortices are designed to solve the problem that the original controller can not control the total righting torque of front and rear fins.The simulation results show that the controller can effectively suppress the problems of low control accuracy,poor anti-roll efficiency and weak adaptability caused by the wake vortices shedding phenomenon on the premise of satisfying the system obstacle avoidance.