| With the rapid development of the UAV industry and the gradual opening of low-level-altitude flight airspace,UAV infrastructure,transportation,communications,agriculture and other civil fields have a wide range of applications,and UAV operation at low altitude and high density has become an inevitable trend.Among them,the UAV-based urban very-low-altitude airspaces logistics transportation industry has the characteristics of low cost,high flexibility,fast delivery,energy saving and environmental protection,leading the development wave of very-low-altitude airspaces.As a key task in the digital management of urban very-low-altitude airspaces,path planning has gradually became a hot topic in UAV research and application.In view of the practical needs,extensive research has been conducted at home and abroad in recent years on the path planning of logistics UAV in the very-low-altitude environment,and various methods of path planning have been proposed.However,there are several problems with existing research at home and abroad,such as:(1)most path planning methods are still stuck in three dimensions,with high invalid airspace occupation,which cannot meet the demands for intensive UAVs use in very-low-altitude airspace;(2)The existing path planning method is not considering the actual operation scenario of UAV logistics,and fails to reduce the loss of life and property caused by the failure from the perspective of path planning;(3)The existing path planning methods fail to make targeted optimization for in-flight replanning scenarios,and cannot avoid secondary conflicts caused by replanning in the time dimension,making it difficult to meet the requirements of high-density operation of logistics UAV.In view of the above problems,this thesis explores the four-dimensional path planning algorithm applicable to future urban air traffic very-low-altitude logistics UAVs in the context of high-density operation of very-low-altitude logistics UAVs,with the reduction of invalid airspace occupancy as the core and the guarantee of UAV flight safety as the fundamental,and from the actual demand,the main research work is as follows:(1)Based on the safety of UAV flight,the risk level cost function of UAV flight is constructed to improve the safety of UAV flight by comprehensively considering the risks existing in the area of building obstacles and inherent ground properties,and the average increase of safety distance is 15.5% as verified by simulation experiments,and can effectively solve the 4D path planning problem of multi-UAV strategic cooperation;(2)To address the problem that the existing replanning methods are prone to secondary conflicts,the path replanning is based on the expected arrival time,which enables the UAV to reach the specified location under the specified time constraint and significantly reduces the generation of secondary conflicts.The simulation experiment verifies that the replanning on-time rate is 98.67%,which proves that the multi-UAV tactical cooperative 4D path planning algorithm can solve the multi-UAV conflict path replanning problem in the tactical stage;(3)In the UAV path planning process,the 4D algorithm is constructed based on the 3D path planning algorithm,which is improved and optimized by incorporating the time dimension to form a multi-UAV collaborative 4D path planning strategy that takes into account the strategic level and tactical level.To sum up,this thesis addresses the practical needs,proposes corresponding improvement measures and related algorithms to shorten the airspace occupation time,improve the airspace utilization,and effectively solve the problem of high-density multi-UAV path planning for urban very-low-altitude logistics transportation in view of the existing problems of path planning for logistics UAVs in the very-low-altitude environment. |
