Research On Equilibrium Of Dynamic Soaring In Gradient Wind And Controller Design

In recent decades,the rapid development of UAVs and their autonomous flight technology has made UAVs widely used in various industries,but the limited energy problem has always been a bottleneck in the development of UAV applications.It is observed that the energy consumed by birds in flight is far less than that of man-made aerial vehicles,because these birds can use gliding techniques to get long flight without flapping their wings under some atmospheric conditions.This kind of soaring technology attracted people's attention before the aircraft was invented.Bird-inspired soaring technology without energy consumption or can reduce energy consumption may bring hope for breaking this bottleneck.Dynamic soaring is a soaring technique that utilizes ununiform natural winds in the atmosphere,but the understanding of it so far is also extremely limited.The work of this paper is as follows(1)The establishment of dynamic model.Based on the wind-fixed coordinate system,a dynamic soaring model and energy model in a horizontal gradient wind environment are established.The singular perturbation theory of the instantaneous equilibrium assumption is analyzed and a 3-degree-of-freedom translational model is established based on the instantaneous equilibrium assumption.Based on the established energy model,the maximum value of the acquired power and the energy boundary in the velocity space are obtained analytically.According to the above analytical expression,the influence of each parameter on the energy boundary is analyzed.(2)The existence of equilibrium points and the analysis of the relevant geometric properties.The equilibrium point of the dynamic model is solved by using the vector relation of the force balance,and the proof of the existence criterion of the equilibrium point is given.The set of the equilibrium points constitutes the equilibrium curve.Through the numerical simulation,the equilibrium curve is divided into ascending and descending curves,and then theoretically proves that the existence of the descending and ascending equilibrium curve,which are necessary and sufficient conditions.According to the existence of the equilibrium curve theorem,an index criterion for the use of engineering is deduced.The criterion can be used to decouple the three factors of environment,aerodynamics and structure.The influence of the optimal lift coefficient,the minimum wind gradient and the wing load is analyzed by this criterion,and the dynamic soaring equilibrium rise in the near space and the Mars environment is investigated.The relationship between the equilibrium curve and the previous chapter of the energy boundary is also studied.(3)Stability and bifurcation analysis of equilibrium curve.In order to reduce the number of influencing parameters,the normalization equation is obtained,and the normalized equilibrium curve is obtained.On the basis of normalization,the stability of the equilibrium curve and the bifurcation of codimension 1 are analyzed with albatross as an example.Based on the bifurcation of codimension 1,the bifurcation of the codimension 2 caused by the change of the wind gradient is discussed,and the influence rule is summarized.(4)The study of dynamic soaring optimal control problem in the case of constant aerodynamic coefficients,especially analyzes the relationship between the equilibrium point and the optimal control.The relationship between the equilibrium point and the optimal control of the cycle is discussed.It is proved that the equilibrium point of the roll angle is the solution of the two-point boundary value problem of the periodic system corresponding to the periodic optimal control.By using the frequency test,the albatross is tested in two cases.The results show that the two cases pass the frequency test and prove that the equilibrium solution when the dynamic gliding has no roll angle is the optimal periodic control.The numerical optimization algorithm is used to verify that the equilibrium solution is not only the optimal periodic control,but also the optimal control which does not depend on the initial value and the time period.(5)An angle of attack controller is designed for the short-period model in the disturbance wind field.Based on the matched uncertainty,the model reference adaptive controller is designed and simulated only in the case of matching uncertainty and adding unmatched uncertainties.Because the model reference adaptive controller is very sensitive to unmatched uncertainty,the robustness of the adaptive controller is improved based on the projective operator,and the simulation result is finally given.The simulation results show that the robust adaptive controller not only has all the advantages of the model reference adaptive controller,but also can effectively suppress the parameter drift caused by the unmatched uncertainty,thus ensuring the overall performance and safety of the controller.In this paper,the equilibrium phenomenon of the dynamic soaring of the unpowered aircraft in the horizontal wind gradient is studied and the controller is designed.The equilibrium point structure in this kind of physical phenomena is proposed and the characteristics of the equilibrium point are systematically discussed.The relationship between the existence and the geometric characteristics,the stability and the bifurcation of the equilibrium point and the optimal control of the equilibrium point are analyzed emphatically.The proposed method and the conclusions obtained provide a theoretical basis for further study of dynamic soaring mechanism and realization of autonomous dynamic soaring.