| In order to accomplish some tasks,vessels in the marine environment need to rely on their own power to maintain the fixed heading and position through dynamic positioning.Thrust allocation is an important module of dynamic positioning system.When the thrust allocation module receives the command of lateral force,longitudinal force and heading rotation force from the dynamic positioning controller,the command thrust is reasonably allocated to each propeller based on the current state of each propeller.The blades of cycloidal propeller are perpendicular to the horizontal plane and rotate around the vertical axis.Because of its unique working principle,cycloid thruster can quickly change the thrust and direction.The excellent maneuverability makes cycloidal propeller become top choice for many vessels with high requirements of safety and maneuverability.In this paper,the surface ship with two channel propellers and two cycloidal propellers is research object,studying how to reasonably and efficiently solve the problem of thrust allocation under task constraints when the object is carrying out tasks.First of all,Analysis of the working principle of the cycloidal propeller and fit the existing hydrodynamic performance data of the cycloidal propeller then to obtain the hydrodynamic performance parameter function so as to build the mathematical model of the cycloidal propeller.With this mathematical model,realize the underlying control of the cycloidal propeller.And then the instruction regulation method of this cycloidal propeller is designed.Secondly,the nonlinear objective function of the thrust allocation problem is designed according to the instruction regulation method,with the mission and mechanical constraints of the propeller,then the control model of the thrust allocation problem is obtained.A novel differential evolution algorithm is proposed in this paper for solving the nonlinear thrust allocation problem with this control model.Finally,the mathematical model of ship motion is given and the dynamic positioning PID controller is designed.The thrust allocation method obtained in the previous paper is combined with the dynamic positioning system in MATLAB for further verification and simulation.The results show that the method of thrust allocation is effective. |
