Research On Modeling And Course-keeping Control Of Podded Propulsion Vessels

Recently,with the development of technology and the improvement of ship performance criteria,podded propulsions(PODs)have been widely used in many types of ships.In order to make the established ship model have good accuracy,a ship motion mathematical model suitable for double podded propulsions ship is established based on the idea of a separated ship model.During the process of modeling,the podded propulsion is discussed and researched separately at first,then the mathematical model of double podded propulsions ship is established,and the research of course-keeping control problem for podded propulsion ship is conducted at last.The main work of this paper is divided into the following points:(1)A 3DOF mathematical ship model of a twin podded propulsion ship is established.During the modeling,the podded propulsion is researched firstly,the effect of hull structure such as skeg is considered.In addition,the interaction effect between pods is considered.Combined with the previous researches on hydrodynamic performance analysis of pods,the thrust and resistance generated by pods,as well as their respective torques,are calculated.Then,taking the double-pod semi-submerged ship “Taiankou” as an example,a separate 3DOF ship model is established.Based on the data of relevant maneuverability tests in the sea trials of real ships,and combining with other literature on the maneuverability of pod propulsion ship,the accuracy of the mathematical model of podded propulsion ship motion was analyzed.(2)The course-keeping ZOH model controller which is suitable for the podded propulsion ship is designed.To reduce the steering frequency,a zero-order holder component is introduced to help the controller design.In the early design of the ZOH model controller,a ZOH component and the ship model are regarded as a whole,that is,the mathematical model of the ZOH ship model.Then the course-keeping controller is designed based on the ZOH ship model.(3)Compared with the rudder of the ship propelled by conventional fixed propulsion,the bow turning moment of pod is larger,which is more likely to cause a larger rolling angle.Considering that most of the podded propulsion vessels are semi-submerged ships or other special vessels,their stability is poor after loading cargo,therefore,the large-angle rotation of the pod must be avoided.The nonlinear feedback technique is introduced to deal with the deviation signal at the input side of the course-keeping ZOH model controller.Then the control algorithm is designed to reduce the control output of the controller as much as possible under the premise of ensuring the course-keeping control performance.Then,the simulation and comparison experiments with other types of course-keeping controllers are carried out in Beaufort No.8 sea state.All the experiments in this paper are programmed by the MATLAB platform.The established 3-DOF ship motion mathematical model of the double-pod propulsion ship has good simulation control accuracy.The simulation results in Beaufort No.8 sea state verify the effectiveness of the proposed course-keeping control algorithm.The research has laid a theoretical foundation for the research of maneuverability and automatic control of propulsion pod and the improvement of marine safety.