Research On Ship Propeller/Rudder/Fin Joint Control

In the research of ships,course control,speed control and roll reduction control are all very important parts in the field of ship control.When a ship sails in the ocean,it must be able to sail according to the preset course and speed.The ship’s course control and speed control are related to the safety and economy of navigation.In addition,many accidents and disasters at sea are related to the rolling of ships,which not only causes serious casualties,but also causes huge economic losses.Three kinds of control devices,propeller,rudder and fin stabilizer,are installed in the ship studied in this paper.Propeller is the motive force of ship motion,which mainly provides a forward force for the ship;rudder mainly keeps the ship in the preset course by changing the rudder angle;fin stabilizer is the best anti-rolling device at present,which reduces roll by adjusting the fin angle to produce different lift.In the course of navigating at sea,the control of ships is actually the control of the three kinds of control devices,so the design of the control system of the three kinds of devices is very important.In addition,due to the decreasing energy consumption,the energy consumed by ships in navigation also needs to be considered.In this paper,the combined control of propeller,rudder and fin is studied,so that the ship can maintain excellent navigation performance and minimize the energy consumption of the control device.Firstly,a Four-Degree-of-Freedom model of ship’s pitching-swaying-rolling-bowing motion is established by using MMG method.The hydrodynamic forces and moments of bare hull without control devices are obtained.The forces and moments of propeller,rudder and fin stabilizer control devices on hull are also calculated.In addition,because the ship will be disturbed by the environment when sailing,the force and moment produced by the wave disturbance on the ship’s four degrees of freedom are also calculated.The influence of the wave on the ship’s speed,course and roll is analyzed through simulation under different sea conditions.In order to overcome the influence of sea waves on ship speed,sailing and rolling,two different controllers are designed to control propellers,rudders and fin stabilizers.The two controllers are PID controller and LQR optimal controller.Among them,the PID controller controls the propeller,rudder and fin separately,so that they control the speed,course and roll of the ship separately.The LQR optimal controller enables the propeller,rudder and fin to control the ship’s speed,course and roll together,and to simulate under three different wave directions.The simulation results show that compared with PID control,LQR combined control can greatly reduce the energy consumption while ensuring the performance of the ship during navigation.Because LQR controller is based on experience to select weighted matrix Q and R,it will consume a lot of time and energy,and in different sea conditions,it can not timely adjust the parameters of the controller,which makes the controller can not guarantee that the performance index can reach the optimal under different sea conditions.So this paper uses genetic algorithm to optimize the weighting matrix of LQR.The simulation results show that the control performance of the system is improved and the energy consumption is basically the same after using genetic algorithm to optimize.