Research On Mechanism And Trajectory Optimization For Unmanned Aerial Vehicles By Dynamic Soaring In Gradient Wind

Long endurance and long distance flight is one of the advancing edges for UAVs'(Unmanned Aerial Vehicles)performance development.This thesis investigates a new flight pattern as a means of green power from atmosphere environment for aircraft.The flight pattern is to make use of periodic dynamic soaring path to extract energy from the wind field in which the physical quantity changed of gradient,without requiring additional propulsive power or little power to fulfill the flight.In nature,dynamic soaring used by albatrosses and other large seabirds to fly for extended periods with hardly a flap of their wings,in some documented cases circumnavigating the globe.Dynamic soaring is an impotant research project in the future with the advantage of zero emission and none pollution.Dynamic soaring can be used as a special flying technique to extract energy from the wind gradient field,and enables UAVs to accomplish the goals of long endurance and long distance.There are many problems need to solve before the application of dynamic soaring,including the parameters perceptive in wind field,the gradient wind energy transfer mechanism,trajectory optimization,multi-purposed optimal design,energy optimal control,autonomous control of UAVs and so on.Among them,how to acquire energy from the gradient wind constantly is one of core issues.So,the thesis aims at better utilization of wind energy,trajectory optimization is one of the key methods of investigation.The thesis has initiated the follows studies:This thesis examines the application of albatrosses' dynamic soaring to UAVs,and investigates dynamic soaring flight as a means of propulsion for UAVs to achieve long endurance and long distance flight.Firstly,the thesis concludes the characteristics of albatross' dynamic soaring,mainly includes the dynamic soaring trajectory and the law of speed variation.Dynamic soaring applied to UAVs are introduced in this paper,including energy extraction mechanism analysis of dynamic soaring,trajectory optimization,trajectory planning and designing methods of dynamic soaring UAV and so on,which can be used as the basis for this thesis.A logarithm model of the wind profile is built based on the observation data of the gradient wind field.The motion equations of UAVs are derived and the energy transfer mechanisms are explained in the gradient wind field.Trajectory optimization is one of the key methods of investigation used in this work.Combined with motion equations,the Hamiltonian canonical equation is chosen to define the boundary conditions of trajectory optimization in dynamic soaring.The boundary conditions include the relationship between minimum wind gradient and wing load of aircraft,the relationship between wind gradient and lift drag ratio,as well as the relationship between wing load and lift drag ratio.Using extreme conditions of Hamiltonian,the range of lift coefficient and roll angle are defined.Secondly,the direction zone of UAVs' optimal trajectory in dynamic soaring is investigated.The zone of direction is converted into cutting-in angle,which is regarded as initial limiting condition in the optimization of dynamic soaring trajectory.The notion of trajectory subsection analysis is applied to account for the energy transformation mechanism during the dynamic soaring,the dynamic soaring trajectory is divided into four phases: climbing with headwind,turning in high altitude,gliding with tailwind,turning in low altitude.During the process of calculating,the gradient wind's direction is taken into decomposition.Accordingly,the relationship between energy gain/loss and cutting-in angle is acquired by means of balance between energy gain and loss.In addition,three dynamic soaring styles corresponding to three typical cutting-in angles(0°,16°,32°)are selected to be analyze intensively,and the explicit characters of trajectories,airspeed,attitude angles and energy variation are presented.In the direction zone of UAVs' optimal dynamic soaring trajectory,a comprehensive study on the performance of long endurance and long distance trajectory optimization of engineless UAV in dynamic soaring is investigated.Long endurance and long distance trajectory optimization problems are modelled by non-linear optimal control equations.Two different boundary conditions are considered and three results are compared:(i)open long endurance pattern,(ii)closed long endurance pattern,(iii)open long distance pattern.Consequently,different mission planning base on dynamic soaring corresponds to different dynamic soaring pattern respectively.In the process of dynamic soaring,the wind relative reference frame of UAVs is not inertial frame in the wind field.In the non-inertial frame,there being an inertial force which is created by gradient wind field.When the wind gradient(GW)and the components of airspeed(vzvx)are positive,inertial force(Fi)makes positive work to the aircraft.In the non-inertial frame,there are four applied forces accounted for the aircraft: lift(L),drag(D),gravitational force(mg)and inertial force(Fi).An equilibrium position principle of dynamic soaring is proposed.At the equilibrium positions,the increased potential energy is greater than the wasted kinetic energy when the aircraft is flying upwards.The mechanical energy is increased in this way,and the aircraft can store energy for flight.According to the extreme value theory,contour line figures of the maximum function and the component of airspeed(vz)are obtained,and it's easy to find out the maximum value of vz,lift coefficient(CL),airspeed(Va),bank angle(?)and the gradient of the wind field are required for the dynamic soaring balance points.To test the capability of the model,experiments are performed.Based on the theoretical results of the dynamic model and simulation,a dynamic soaring experiment is designed and conducted.In the experiments,it can be found that under the constraints of several parameters,such as flight path angle and heading angle,the aircraft can absorb energy from the wind field by means of dynamic soaring.In a word,flying without fuel is feasible.Additionally,by performing the numerical simulation,an optimized trajectory can be found which provides guidance for real flight.Finally,based on equilibrium position principle and dynamic soaring experiment,a control system for autonomous dynamic soaring is designed.The control system is implemented through the multiple closed loop control structure by state full feedback and control variable feedback.The design is the theoretical exploration for autonomous control in dynamic soaring.Experiment results illustrated that the autonomous control algorithm has good tracking performance.The study makes the foundation for the further trajectory planning and tracking.Dynamic soaring in wind gradient of UAVs are studied in this thesis,the studying contents including dynamic modeling of aircraft,energy extraction mechanism analysis of dynamic soaring,trajectory optimization,strategy analysis of gradient wind utilization,autonomous control of UAVs and so on.The above studies can provide design thoughts and analysis method for UAVs' long endurance and long distance flight,meanwhile,these studies can provide technical support for trajectory optimization for dynamic soaring in terms of mission planning.The thesis is very impotant for exploring new energy for UAVs.