Research On Motion Modeling Based On CFD And Control Method For DP Ship

The research of DP control centers on how to maintain a good control effect in complex marine environment. A accurate ship motion mathematical model is the basis of DP control,and the hydrodynamic coefficients is the important part of the motion mathematical model .Three methods are now mainly used to calculate the hydrodynamic parameters,physical pool test method, empirical formula estimation method and numerical simulation method based on CFD. The method of physical pool test method is time-consuming, high-cost and has scale effect, furthermore, empirical formula estimation method is restricted by ship type, and the calculation accuracy is not high. The method using CFD for numerical simulation experiment is convenient, low-cost, comprehensive flow filed information and rapidly developed. So, the paper uses CFD method to simulate the constrained ship model test,it pays attention to the modeling method and DP system controller design of the DP ship. The work contains several aspects as following:Firstly, building mathematic model of three degree of freedom for DP ship. Making using of Fossen modeling method, combing with the traits of low speed of DP ship, the paper simplifies the general ship hydrodynamic mathematical model and builds a simple but reasonable hydrodynamic model, on this basis, the three degree of freedom mathematical model applied to target ship is built.Secondly, making use of CFD to simulate the constrained ship model test to measure the hydrodynamic parameters. The target ship's 3D model is drawn,and scaled according to 1:20.For numerical calculation, the 3D model is meshed using ICEM CFD. On this basis, three kinds of numerical simulations test of a ship are conducted using FLUENT, including the direct test, towing test and rotating arm test, getting the hydrodynamic value and the force distance value. By fitting the computing results in use of the least square method, the hydrodynamic coefficients are easily calculated. By comparing the computing results with experimental results and verifying the ship model, this numerical calculation method is proved to be effective and the established model is proved to be correct.Finally, design of DP controller. There are certain errors in the model parameters calculated by CFD and unknown external environmental disturbance. The back-stepping control method and RBF neural network are combined to design an adaptive controller independent of ship model parameters. This controller is designed to deal with the nonlinear parts of model and estimate external environmental disturbance...