Research On Key Tecnologies Of Structural And Flight Dynamics For A Composite Unmanned Aerial Vehicle

Due to the objective of structural flexibility,structural vibrations,aerodynamic forces and flight status are unavoidably coupled together when the unmanned aerial vehicles(UAVs)are in the flight process,the coupling moment affects the UAV flight process.With the gradual development of the aircraft lightweight design and the extensive use of the composite materials,the structural flexibility gets more and more obvious and the coupling on the UAV flight process has become more prominent,so the need to consider the effects of the structural flexibility in the design and analysis of UAVs has become even more urgent.In view of the above problems,the paper regarded the composite wing as the main research object,and carried out the flight process analysis of a UAV considering the effect of structural flexibility on the UAV flight process,with the multidisciplinary collaborative of the structural dynamics,the flight dynamics and the aerodynamics.The main contents of the paper include the following aspects:1.Study on the nonlinear dynamics modeling of the composite wing.The nonlinear modeling is the basis of dynamics analysis.Due to the complex material nature and the special process conditions,composite materials have obvious uncertainties.And the structural dynamics of the wing contains significant nonlinearity during the UAV flight process.Regarding the issue above,in this paper the nonlinear dynamics modeling of the composite wing was built by identification technique.In order to reduce the complexity of the nonlinear dynamics modeling and increase the speed of the nonlinear solution,the modes of the composite wing were sorted and truncated according to the modal contribution theory.2.Study on the unsteady aerodynamic forces of the composite wing.The unsteady aerodynamic forces are the main external loads to the research of the UAV flight process.In this paper,the unsteady aerodynamic forces of the composite wing were obtained by the fluid-solid coupling of the computational structural dynamics and the computational fluid dynamics.In the fluid-solid coupling,the structural modeling was the nonlinear dynamics modeling of the composite wing and the fluid dynamics analysis was carried out in the commercial computational fluid dynamics software Fluent.The coupling between the nonlinear dynamics modeling and the software Fluent was done by the User-Defined Function,the data interaction is based on the radial basis function theory,and the fluid-solid coupling method is the tight method.The results of the subsequent analysis show that the lift force of the composite wing decreases gradually with the increase of the wing deformation,the drag force has the same trend with the lift force,and the pitching moment increases with the increase of the wing deformation.3.Study on the modeling of the UAV flight dynamics.First,in order to accurately describe the UAV motion state,this paper defined the coordinate systems required by the flight equation,and the transformation matrixes between the different coordinate systems.Then,the paper defined the parameters used to describe the UAV flight status,such as the attitude angle,airflow angle,line speed and angular velocity.Secondly,the expressions of aerodynamic forces and moments,engine thrust and torque,ground forces and moments and UAV's gravity in the process of ejection,flight and ground motion were given in this paper.Finally,based on the Bryan model and the loads applied on the UAV,flight dynamics models of the UAV at different stages were established.4.Multidisciplinary collaborative analysis of the UAV flight process.In this paper,the multidisciplinary collaborative approach and the complete analysis process of the UAV flight process analysis were established,based on the interrelationship among the aerodynamics,the structural dynamics and the flight dynamics.Two flight process analysis were carried out with the difference that whether to consider the flexibility of the wing.The comparison with the results of a flight test show that results of the analysis that ignore the wing flexibility have big difference with those of the flight test,and the results of the multidisciplinary collaborative analysis are very closer to the test results.Finally,the flutter analysis of the composite wing was carried out and the flutter velocity of the composite wing at different angles of attack were obtained.The paper regarded the composite wing as the main research object,and carried out flight process analysis of a UAV considering the effect of structural flexibility on the UAV flight process,with the four key technologies of nonlinear dynamic modeling method of composite materials,unsteady aerodynamic load calculation method,UAV flight dynamic modeling method and multidisciplinary collaborative analysis method.The comparison with the flight test results shows that the multidisciplinary collaborative analysis method established in this paper can effectively overcome the shortcomings of the rigid hypothesis analysis method,and it is of great significance not only to ensure the accuracy of UAV flight analysis results,but also to the safety and stability of the control and flight of UAV.