Research On Structure Optimization Of Unmanned Aerial Vehicle System In Turbulent Wind Field Environment

The unmanned aerial vehicle is an aircraft that flying with remote control or according to an autonomous program.It is widely used in the military and civilian fields.In recent years,due to the flexibility of the multi-rotor unmanned aerial vehicles,the ability to take off and land vertically,and the small size have become the research hotspots.However,in the low-altitude and low-speed flight environment,the multi-rotor unmanned aerial vehicles have the problem of being susceptible to the turbulent wind field,thus reducing them flight performance and flight quality.At present,the stability research of the multi-rotor unmanned aerial vehicles in turbulent wind field environment is mainly focused on the flight control algorithm of the unmanned aerial vehicles.There are few studies on system structure.In order to reduce the adverse effects of turbulent wind field,make up for the shortcomings of control algorithms and improve flight performance and flight quality,the hex-rotor unmanned aerial vehicle is taken as an example,combined with structural optimization theory and finite element analysis theory for optimization research.The main research work is as follows:(1)Firstly,the structure and flight principle of the hex-rotor unmanned aerial vehicle are studied.According to the data of take-off quality and flight speed,the overall performance parameters of the hex-rotor unmanned aerial vehicle structure are determined.Then,the threedimensional model of the structure of the hex-rotor unmanned aerial vehicle system is established by Solidworks,and the dynamic model is established according to the Newton-Euler theorem,which laid the simulation foundation for the later structural analysis and optimization.(2)The characteristics of rotor aerodynamics and turbulent wind field are analyzed.The dynamic model and turbulent wind field model of hex-rotor unmanned aerial vehicle under turbulent wind field are established respectively.The linear filtering method is used to simulate the turbulent wind field.The turbulent wind velocity time history,turbulent wind pressure and turbulent wind velocity power spectral density image are obtained,and the wind load data is also obtained.Through the comparative analysis of the simulated spectrum and the target spectrum,the feasibility of the numerical simulation results is verified,which provides data basis for subsequent analysis and research.(3)Based on the finite element model of the hex-rotor unmanned aerial vehicle system structure,the static analysis of the structure of the hex-rotor unmanned aerial vehicle system in the turbulent wind field environment is carried out.It is found that the overall structural strength of the fuselage fully meets the design requirements of the unmanned aerial vehicle flying at maximum flight speed in the four-level wind environment,which proves that there is design redundancy in the overall structure of the fuselage;the free modal analysis of the structure of the hex-rotor unmanned aerial vehicle system show that the natural frequency of the fuselage structure is concentrated at 9 Hz to 67 Hz,and the turbulent wind field frequency is concentrated at 0 Hz to 10 Hz.When the two frequencies cross,resonance is very likely to occur.Random loads obtained from four winds are used for random vibration analysis,witch the result shows that the maximum stress of the overall structure of the fuselage is less than the fatigue limit of the PA66 and Carbon fiber T300,and fatigue damage and damage will not occur.(4)Aiming at the problem of redundant design and easy resonance of the hex-rotor unmanned aerial vehicle system under turbulent wind field,optimization analysis and design are carried out.Firstly,the Topology Optimization is used to optimize the overall structure of the fuselage,and then the Size Optimization and Shape Optimization are used to optimize the size and shape of each part of the structure.The optimal design variables are determined by sensitivity analysis.The structural strength and displacement are used as the constraint,and the minimum mass is used as the objective function to obtain the optimal design scheme.Finally,the model is re-modeled according to the optimization result,and the optimized model is simulated and verified.The simulation experiment is carried out under the condition that the unmanned aerial vehicle is flying at the maximum flight speed in the four-level wind environment.The result analysis shows that the take-off quality of unmanned aerial vehicle is reduced,the load capacity is improved,the fuselage structure vibration is reduced,and the adversely affected of the turbulent wind field is reduced,flight performance and flight quality is improved.