Study On Navigation Safety Domain And Collision Avoidance Decision-making Support Of USV Based On COLREGs

In recent years,with the rapid development of intelligent technology and robot technology,multitudinous high-tech marine equipment have emerged.Among them,the unmanned surface vehicles(USVs)are platforms which can perform tasks independently in ocean and rivers,they are the prime embodiment of the application of autonomous technology in the surface environment.The safety of USVs’ activities is a priority issue in their applications,it is an effective method to ensure that by delimiting a reasonable navigation safety domain around the USV to reduce the collision risk in the process of encounter.Whereas the model of navigation safety domain of USVs is rarely studied,most of them are simplified models of manned ships.Therefore,a navigation safety domain specific suitable for USVs was proposed in this thesis,and the collision avoidance decision-making support method was studied based on this model.Firstly,the basic navigation safety domain model was obtained by improving the quaternion ship domain.This model can calculate the size of safety domain to be maintained during navigation according to the dimension parameters,maneuverability parameters and encounter parameters of USV.Considering the variability of encounter situation and the complexity of environment during the navigation of USVs,the overtaken situation was added on the basis of the head-on,crossing and overtaking situation which are stipulated in the COLREGs(International Regulations for Preventing Collisions at Sea).Taking the Dolphin-I catamaran as the study object,the relevant parameters were obtained through the field experiment and the rationality of the model was verified.Then,the essential factors which could affect the navigation safety of USVs were extracted via rough set,the extension functions of these factors were carried out to model the dynamic navigation safety domain(DNSD).The proposed model comprehensively considers the influence of environmental factors during navigation and can provide a dynamic safety domain according to the change of environment.The above mentioned catamaran was taken as the simulation study object and the DNSD was employed in various working conditions and compared with the ship domain models of manned ships.The simulation results elucidated that the dynamic navigation safety domain can automatically modify the domain scale according to the change of working conditions.Compared with the ship domain models of manned ship like the Fujii model and the Coldwell model,the DNSD can provide more reasonable safety area for USVs’ action of collision avoidance.Finally,to improve the accuracy of the collision avoidance decision-making of USVs,a collision risk calculation model based on navigation safety domain and collision risk index(CRI)was proposed in this thesis.The model can accurately calculate the collision risk value in any direction and the collision stage in the encounter process,and provide support for the collision avoidance decision of the USV.The reliability of the collision risk calculation model was validated by experiments in various scenarios.At the same time,for each collision stage judged by this method,the specific provisions of COLREGs that should be followed in each case were summarized for the subsequent design of USV intelligent navigation system.The navigation safety domain and collision avoidance decision support model proposed in this thesis have laid a preliminary foundation for the development of intelligent navigation system of unmanned vessels,and play a certain role in promoting the realization of autonomous navigation of USVs in the future.