Path Planning And Following Algorithms For Underactuated Ships

With the promotion of maritime strategy of our county,the researches about the ship motion control become more and more important in recent years.As a main form of surface vessels,the underactuated ship has its significance.This thesis is about the motion control of surface vessels.We select underactuated ships as our target and solve two main problems,path planning and path following,on this topic.We propose new approaches in this field.In addition,visualization platform for maritime simulation is developed in our work.The main contents of our work are shown below:(1)Path planning algorithm for underactuated ships is discussed in the thesis.In our approach,we use the planning algorithm based on map grids.A heuristic A* algorithm is utilized to ensure the efficiency of the proposed algorithm.By reasonable assumption on the real situations of target ship and obstacles,we induce the concepts of penalty factor and distance of the closest point of approach(DCPA)to the solution.We implement the algorithm and test it under different situations with different settings of target ship and obstacles.The experiment verifies the accuracy and efficiency of the proposed method.(2)Path following algorithm for underactuated ships is discussed in the thesis.We combined the typical line-of-sight guidance law and neural network controller to fulfill the control task.In the proposed approach,firstly we discuss the line-of-sight guidance law under two different situations.Then we combine the guidance law with the reinforcement learning based neural network(RLNN)controller and take the saturation of the rudder angle into consideration.As a model free controller,the RLNN controller solves the path following problem and provide a novel approach to this problem.At last,we simulated the controller to the target ship to make it converged to the generated paths.(3)A maritime simulation platform is developed in the thesis.Combined with the real cases,we develop three main features: path generation,path replay and maneuvering simulation.Different from current platforms,we use Unity as the development platform to realize realistic 3D ship and ocean.For path generation,we use second order system model to generate reference paths for the target ship;for path replay,we use interpolation to smooth the frame effects and we calculate distance among ships via rotating caliper algorithm;for maneuvering simulation,we use the model proposed by Maneuvering Modeling Group(MMG).