Route Planning Of Offshore Ships Based On Improved A~* Algorithm

The effective utilization of marine resources is one of the key points in the current marine strategy.With the increase of artificial facilities at sea,the navigation environment at sea has changed.The marine equipment can be regarded as a kind of fixed obstacle on the sea,which increases the danger of the nearby normal navigable ships.On the other hand,some ships have to transport personnel and materials near obstacles when these facilities need maintenance.It is of great significance for a ship to find a safe shortest path.As a classic path planning algorithm,A~* algorithm is easy to use and can find the global optimal path in a static environment.In this paper,a multidirectional A~* algorithm for ship path planning is proposed based on A~* algorithm.In this process,the artificial potential field is used for reference to improve the search map through image processing and obstacle environment modeling while the traditional A~* algorithm is used for reference to generate the neighborhood nodes by changing the mobile step size.The specific practice is as follows:(1)The basic theory of heuristic algorithm is studied,and the implementation process and existing defects of artificial potential field and traditional A~* algorithm are analyzed.In this way,it lay a solid foundation for improving the A~* algorithm by combining them.(2)At the process of building a search map for A~* algorithm,first of all the navigable navigation information is extracted from the image processing of the sea chart.And then the pixels are used as the basic units to describe the position of the obstacle.Next the artificial potential field theory is used to establish the virtual repulsion potential field model based on the characteristics of the obstacles and the environment conditions of the ship.Finally,the repulsive force is converted to the penalty value of the ship to calculate the penalty matrix.(3)In the path point generation,the fundamental reason for the path direction limitation of the traditional A~* algorithm is first analyzed,and then a circular domain generation method is proposed.In this method,the node accessibility is used to ensure that the planning path can satisfy the ship motion law,while the path smoothing is realized by using the adjacent node optimization algorithm and the key point iteration algorithm.(4)The proposed method is applied to simulate the path planning of wind turbine maintenance in Donghai Bridge offshore wind farm,and the simulation results show that the simulation path is very similar to the actual path.On this basis,we use computer automatically calculate the optimal path by set the start location,the terminal location and where the ship must approach.The calculation illustrates that the path can meet the needs of the shortest path or the minimum cost.