Dynamic soaring is a flight maneuver to exploit gradient wind field to extend endurance and traveling distance.Optimal trajectories for permissible wind conditions are generated for loitering dynamic soaring as well a...Dynamic soaring is a flight maneuver to exploit gradient wind field to extend endurance and traveling distance.Optimal trajectories for permissible wind conditions are generated for loitering dynamic soaring as well as for traveling patterns with a small unmanned aerial vehicle.The efficient direct collection approach based on the Runge-Kutta integrator is used to solve the optimization problem.The fast convergence of the optimization process leads to the potential for real-time applications.Based on the results of trajectory optimizations,the general permissible wind conditions which involve the allowable power law exponents and feasible reference wind strengths supporting dynamic soaring are proposed.Increasing the smallest allowable wingtip clearance to trade for robustness and safety of the vehicle system and improving the maximum traveling speed results in shrunken permissible domain of wind conditions for loitering and traveling dynamic soaring respectively.Sensitivity analyses of vehicle model parameters show that properly reducing the wingspan and increasing the maximum lift-to-drag ratio and the wing loading can enlarge the permissible domain.Permissible domains for different traveling directions show that the downwind dynamic soaring benefitting from the drift is more efficient than the upwind traveling pattern in terms of permissible domain size and net traveling speed.展开更多
The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins ...The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins model is used to approximate the dynamics of UAVs.Based on the assumption,the path planning problem of UAVs in MTST can be formulated as a Dubins traveling salesman problem(DTSP).By considering its prohibitively high computational cost,the Dubins paths under terminal heading relaxation are introduced,which leads to significant reduction of the optimization scale and difficulty of the whole problem.Meanwhile,in view of the impact of wind on UAVs' paths,the notion of virtual target is proposed.The application of the idea successfully converts the Dubins path planning problem from an initial configuration to a target in wind into a problem of finding the minimal root of a transcendental equation.Then,the Dubins tour is derived by using differential evolution(DE) algorithm which employs random-key encoding technique to optimize the visiting sequence of waypoints.Finally,the effectiveness and efficiency of the proposed algorithm are demonstrated through computational experiments.Numerical results exhibit that the proposed algorithm can produce high quality solutions to the problem.展开更多
This paper presents a nonlinear robust control design method for a generic rotorcraft unmanned aerial vehicle(RUAV). The control objective is to let the RUAV track some pre-defined time-varying position and heading tr...This paper presents a nonlinear robust control design method for a generic rotorcraft unmanned aerial vehicle(RUAV). The control objective is to let the RUAV track some pre-defined time-varying position and heading trajectories. The proposed controller employs feedback linearization process to realize the dynamic decoupling control and applies adaptive sliding mode control to compensate for the parametric uncertainties and external disturbances. The global asymptotical stability is proved via stability analysis. Compared with the cascaded controller, the proposed controller demonstrates a superior tracking performance and robustness through numerical simulation in the presence of parametric uncertainties and unknown disturbances.展开更多
Since the 2010s,unmanned aerial vehicle(UAV)sprayer was applied more and more widely for low-volume aerial pesticides spraying operations in China.However,droplets from the UAV sprayer have a higher drift risk due to ...Since the 2010s,unmanned aerial vehicle(UAV)sprayer was applied more and more widely for low-volume aerial pesticides spraying operations in China.However,droplets from the UAV sprayer have a higher drift risk due to more fine droplets sprayed and a higher flight height than ground sprayers.Study on UAV spray drift has been a new hot spot within the field of pesticide application technology.Most of previous studies used direct field methods for spray drift,but the meteorological conditions in field were unstable and uncontrollable,and drift research under an actual operation state in wind tunnel has not been reported.Therefore,25 treatments of wind tunnel measurements and droplets spectrum tests of 10 models of nozzles were conducted to explore the influence factor on spray drift characteristics of UAV chemicals application in this study.A spray unit with a rotor of UAV was innovatively installed in wind tunnel,and the airstream from the wind tunnel was regarded as the relative moving natural wind to simulate the flight status.The airborne and the sediment spray drift was measured to study the effects of the nozzle type and size(flat fan,hollow cone and air-inclusion nozzles),flight speed,adjuvant(DRS-60,Y-20079,MF and G-611)and meteorological parameters(20°C&40%,20°C&80%,30°C&40%and 30°C&60%).The drift potential(DP)and the drift potential reduction percentage(DPRP)in vertical and horizontal directions were obtained for each test.Both nozzle type and size had an impact on the spray drift potential obviously by affecting the droplet size and the ratio of fine droplets,and the regression linear models between DPRPV/DPRPH and DV50,V75 were established(R2=0.934/0.925).Flight speed also had a significant effect on the spray drift characteristics,and reducing the flight speed could increase the DP effectively.Adding spray adjuvants could affect the DP under experimental meteorological parameters,and the anti-drift performance ranked in the order of DRS-60>MF>Y-20079>G-611.Recommendations were proposed in order to reduce the spray drift for UAV sprayer’s operation.These findings can contribute to provide guidelines and technical support for the wind tunnel spray drift tests of UAV and the field operation regulation of unmanned aerial PPP application.展开更多
Aiming at the requirements of accurate target positioning and autonomous capability for adapting to the environmental changes of unmanned aerial vehicle(UAV),a new method for wind estimation and airspeed calibration i...Aiming at the requirements of accurate target positioning and autonomous capability for adapting to the environmental changes of unmanned aerial vehicle(UAV),a new method for wind estimation and airspeed calibration is proposed.The method is implemented to obtain both wind speed and wind direction based on the information from a GPS receiver,an air data computer and a magnetic compass,combining with the velocity vector triangle relationships among ground speed,wind speed and air speed.Considering the installation error of Pitot tube,cubature Kalman filter(CKF)is applied to determine proportionality calibration coefficient of true airspeed,thus improving the accuracy of wind field information further.The entire autonomous flight simulation is performed in a constant 2-D wind using a digital simulation platform for UAV.Simulation results show that the wind speed and wind direction can be accurately estimated both in straight line and in turning segment during the path tracking by using the proposed method.The measurement accuracies of the wind speed and wind direction are 0.62 m/s and2.57°,respectively.展开更多
The turbulence or gust in quadrotor flight environment causes drastic changes in the unmanned aerial vehicle(UAV)aerodynamic parameters.Especially,rotor thrust coefficient and reaction torque coefficient of the UAV en...The turbulence or gust in quadrotor flight environment causes drastic changes in the unmanned aerial vehicle(UAV)aerodynamic parameters.Especially,rotor thrust coefficient and reaction torque coefficient of the UAV encounter uncertainty fluctuation,which may undermine the control performance.A real-time estimation strategy for these aerodynamic parameters is proposed to improve the identification on the disturbance.First,the unscented Kalman filter(UKF)algorithm is used to estimate the UAV states and aerodynamic parameters.Then,a double-loop structure,consisting of position and attitude,is designed for the trajectory tracking control.In the outer loop,a proportional-derivative controller is adopted to carry out position tracking and provide Euler angle references for the inner loop,called attitude controller.Moreover,the attitude controller is designed using an inverse dynamic technique.The main contribution of this study is to propose a joint estimation on the aerodynamic parameters with wind disturbance as well as the UAV states.This strategy plays an important role in refining time-varying parameters of wind disturbance.A number of simulations are executed to verify the effectiveness of the proposed method.展开更多
Tropical cyclones and cyclogenesis are active areas of research. Chute-operated dropsondes are capable of acquiring high resolution vertical wind profile of tropical cyclones. This work proposes a chute-free vertical ...Tropical cyclones and cyclogenesis are active areas of research. Chute-operated dropsondes are capable of acquiring high resolution vertical wind profile of tropical cyclones. This work proposes a chute-free vertical retardation technique (termed as spinsonde) that can accurately measure vertical wind speed profile. Unlike the expendable dropsondes, the spinsonde allows multi-cycle measurement to be performed within a single flight. Proof of principle is demonstrated via simulation and results indicate that the ground speed correlates with the wind speeds to within ±5 km·h-1. This technique reduces flying weight and increases payload capacity by eliminating bulky chutes. Maximum cruising speed (VH) achieved by the spinsonde UAV is 368 km·h-1.展开更多
旋翼无人机空气动力学模型能够克服无人机旋翼下洗气流的影响,相比携带传感器直接测风具有一定优势。空气动力学模型利用无人机自身的姿态数据可以直接计算得到风向,但是风速的计算还需要开展大量的风洞实验以及复杂的实体建模获取相关...旋翼无人机空气动力学模型能够克服无人机旋翼下洗气流的影响,相比携带传感器直接测风具有一定优势。空气动力学模型利用无人机自身的姿态数据可以直接计算得到风向,但是风速的计算还需要开展大量的风洞实验以及复杂的实体建模获取相关参数。为简化流程、规避参数获取过程中存在的误差,采用BP(back propagation)神经网络替代风洞实验和实体建模,研究无人机姿态同自然风速的关系。通过确定风速影响因子,分别建立以两个欧拉角为输入和以两个欧拉角计算得到的倾角为输入的旋翼无人机空中原位风速反演模型EUL-BP(euler back propagation)和INC-BP(incline back propagation)。以无人机悬停等高度风塔上超声风速仪观测自然风速为真值,比较反演模型EUL-BP和INC-BP发现,INC-BP增强了BP神经网络寻优过程的约束,反演效果较EUL-BP更优,其均方根误差大致为0.65 m/s,相关系数为0.86左右;比较反演模型结果与无人机机载自动气象站观测结果发现,当风力条件为三级及以下时,反演风速远优于携带传感器观测的风速。展开更多
Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings signific...Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings significant aerodynamic interference to the ducted fan,which seriously threatens flight stability and safety.In this work,the numerical simulation with the Unsteady Reynolds Averaged Navier-Stokes(URANS)method and the sliding mesh technique is performed to evaluate the steady wind effect.The results show that the wind will lead to serious unsteady effects in the flow field,and the thrust fluctuates at the blade passing frequency of 200 Hz.As the wind speed increases,the rotor thrust increases,the duct thrust decreases,and the total thrust changes little.Flow instability may occur when the wind speed exceeds 8 m/s.As the angle of low-speed wind increases,the rotor thrust changes little,the duct thrust increases,and the total thrust increases.In addition,we figure out that cases with the same crosswind ratio are similar in results,and increasing the rotating speed or fan radius is beneficial to performance improvement in wind.The findings are essential to the ducted fan design and UAV flight control design for stable and safe operations in wind conditions.展开更多
文摘Dynamic soaring is a flight maneuver to exploit gradient wind field to extend endurance and traveling distance.Optimal trajectories for permissible wind conditions are generated for loitering dynamic soaring as well as for traveling patterns with a small unmanned aerial vehicle.The efficient direct collection approach based on the Runge-Kutta integrator is used to solve the optimization problem.The fast convergence of the optimization process leads to the potential for real-time applications.Based on the results of trajectory optimizations,the general permissible wind conditions which involve the allowable power law exponents and feasible reference wind strengths supporting dynamic soaring are proposed.Increasing the smallest allowable wingtip clearance to trade for robustness and safety of the vehicle system and improving the maximum traveling speed results in shrunken permissible domain of wind conditions for loitering and traveling dynamic soaring respectively.Sensitivity analyses of vehicle model parameters show that properly reducing the wingspan and increasing the maximum lift-to-drag ratio and the wing loading can enlarge the permissible domain.Permissible domains for different traveling directions show that the downwind dynamic soaring benefitting from the drift is more efficient than the upwind traveling pattern in terms of permissible domain size and net traveling speed.
基金Project(61120106010)supported by the Projects of Major International(Regional)Joint Research Program Nature Science Foundation of ChinaProject(61304215,61203078)supported by National Natural Science Foundation of China+1 种基金Project(2013000704)supported by the Beijing Outstanding Ph.D.Program Mentor,ChinaProject(61321002)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China
文摘The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins model is used to approximate the dynamics of UAVs.Based on the assumption,the path planning problem of UAVs in MTST can be formulated as a Dubins traveling salesman problem(DTSP).By considering its prohibitively high computational cost,the Dubins paths under terminal heading relaxation are introduced,which leads to significant reduction of the optimization scale and difficulty of the whole problem.Meanwhile,in view of the impact of wind on UAVs' paths,the notion of virtual target is proposed.The application of the idea successfully converts the Dubins path planning problem from an initial configuration to a target in wind into a problem of finding the minimal root of a transcendental equation.Then,the Dubins tour is derived by using differential evolution(DE) algorithm which employs random-key encoding technique to optimize the visiting sequence of waypoints.Finally,the effectiveness and efficiency of the proposed algorithm are demonstrated through computational experiments.Numerical results exhibit that the proposed algorithm can produce high quality solutions to the problem.
基金Supported by the Natural Science Foundation of Tianjin(14JCZDJC31900)
文摘This paper presents a nonlinear robust control design method for a generic rotorcraft unmanned aerial vehicle(RUAV). The control objective is to let the RUAV track some pre-defined time-varying position and heading trajectories. The proposed controller employs feedback linearization process to realize the dynamic decoupling control and applies adaptive sliding mode control to compensate for the parametric uncertainties and external disturbances. The global asymptotical stability is proved via stability analysis. Compared with the cascaded controller, the proposed controller demonstrates a superior tracking performance and robustness through numerical simulation in the presence of parametric uncertainties and unknown disturbances.
基金This study was supported by Sino-German Cooperation Project(31761133019)supported by National Natural Science Foundation of China,National Key R&D Program of China(2017YFD0200304)+1 种基金and China Postdoctoral Science Foundation Funded Project(2019M650907)The authors would like to thank Mr.Sven Nolten and other staff of Institute for Application Techniques in Plant Protection,JKI and all staff of CCAT,China Agricultural University for their contributions to this work.
文摘Since the 2010s,unmanned aerial vehicle(UAV)sprayer was applied more and more widely for low-volume aerial pesticides spraying operations in China.However,droplets from the UAV sprayer have a higher drift risk due to more fine droplets sprayed and a higher flight height than ground sprayers.Study on UAV spray drift has been a new hot spot within the field of pesticide application technology.Most of previous studies used direct field methods for spray drift,but the meteorological conditions in field were unstable and uncontrollable,and drift research under an actual operation state in wind tunnel has not been reported.Therefore,25 treatments of wind tunnel measurements and droplets spectrum tests of 10 models of nozzles were conducted to explore the influence factor on spray drift characteristics of UAV chemicals application in this study.A spray unit with a rotor of UAV was innovatively installed in wind tunnel,and the airstream from the wind tunnel was regarded as the relative moving natural wind to simulate the flight status.The airborne and the sediment spray drift was measured to study the effects of the nozzle type and size(flat fan,hollow cone and air-inclusion nozzles),flight speed,adjuvant(DRS-60,Y-20079,MF and G-611)and meteorological parameters(20°C&40%,20°C&80%,30°C&40%and 30°C&60%).The drift potential(DP)and the drift potential reduction percentage(DPRP)in vertical and horizontal directions were obtained for each test.Both nozzle type and size had an impact on the spray drift potential obviously by affecting the droplet size and the ratio of fine droplets,and the regression linear models between DPRPV/DPRPH and DV50,V75 were established(R2=0.934/0.925).Flight speed also had a significant effect on the spray drift characteristics,and reducing the flight speed could increase the DP effectively.Adding spray adjuvants could affect the DP under experimental meteorological parameters,and the anti-drift performance ranked in the order of DRS-60>MF>Y-20079>G-611.Recommendations were proposed in order to reduce the spray drift for UAV sprayer’s operation.These findings can contribute to provide guidelines and technical support for the wind tunnel spray drift tests of UAV and the field operation regulation of unmanned aerial PPP application.
基金supported by the Pre-research Foundation of Chinese People's Liberation Army General Equipment Department(No.51325010601)
文摘Aiming at the requirements of accurate target positioning and autonomous capability for adapting to the environmental changes of unmanned aerial vehicle(UAV),a new method for wind estimation and airspeed calibration is proposed.The method is implemented to obtain both wind speed and wind direction based on the information from a GPS receiver,an air data computer and a magnetic compass,combining with the velocity vector triangle relationships among ground speed,wind speed and air speed.Considering the installation error of Pitot tube,cubature Kalman filter(CKF)is applied to determine proportionality calibration coefficient of true airspeed,thus improving the accuracy of wind field information further.The entire autonomous flight simulation is performed in a constant 2-D wind using a digital simulation platform for UAV.Simulation results show that the wind speed and wind direction can be accurately estimated both in straight line and in turning segment during the path tracking by using the proposed method.The measurement accuracies of the wind speed and wind direction are 0.62 m/s and2.57°,respectively.
基金Supported by the National Natural Science Foundation of China(No.61703314,61573263)National Key Research and Development Program of China(No.2017YFC0806503)
文摘The turbulence or gust in quadrotor flight environment causes drastic changes in the unmanned aerial vehicle(UAV)aerodynamic parameters.Especially,rotor thrust coefficient and reaction torque coefficient of the UAV encounter uncertainty fluctuation,which may undermine the control performance.A real-time estimation strategy for these aerodynamic parameters is proposed to improve the identification on the disturbance.First,the unscented Kalman filter(UKF)algorithm is used to estimate the UAV states and aerodynamic parameters.Then,a double-loop structure,consisting of position and attitude,is designed for the trajectory tracking control.In the outer loop,a proportional-derivative controller is adopted to carry out position tracking and provide Euler angle references for the inner loop,called attitude controller.Moreover,the attitude controller is designed using an inverse dynamic technique.The main contribution of this study is to propose a joint estimation on the aerodynamic parameters with wind disturbance as well as the UAV states.This strategy plays an important role in refining time-varying parameters of wind disturbance.A number of simulations are executed to verify the effectiveness of the proposed method.
文摘Tropical cyclones and cyclogenesis are active areas of research. Chute-operated dropsondes are capable of acquiring high resolution vertical wind profile of tropical cyclones. This work proposes a chute-free vertical retardation technique (termed as spinsonde) that can accurately measure vertical wind speed profile. Unlike the expendable dropsondes, the spinsonde allows multi-cycle measurement to be performed within a single flight. Proof of principle is demonstrated via simulation and results indicate that the ground speed correlates with the wind speeds to within ±5 km·h-1. This technique reduces flying weight and increases payload capacity by eliminating bulky chutes. Maximum cruising speed (VH) achieved by the spinsonde UAV is 368 km·h-1.
文摘旋翼无人机空气动力学模型能够克服无人机旋翼下洗气流的影响,相比携带传感器直接测风具有一定优势。空气动力学模型利用无人机自身的姿态数据可以直接计算得到风向,但是风速的计算还需要开展大量的风洞实验以及复杂的实体建模获取相关参数。为简化流程、规避参数获取过程中存在的误差,采用BP(back propagation)神经网络替代风洞实验和实体建模,研究无人机姿态同自然风速的关系。通过确定风速影响因子,分别建立以两个欧拉角为输入和以两个欧拉角计算得到的倾角为输入的旋翼无人机空中原位风速反演模型EUL-BP(euler back propagation)和INC-BP(incline back propagation)。以无人机悬停等高度风塔上超声风速仪观测自然风速为真值,比较反演模型EUL-BP和INC-BP发现,INC-BP增强了BP神经网络寻优过程的约束,反演效果较EUL-BP更优,其均方根误差大致为0.65 m/s,相关系数为0.86左右;比较反演模型结果与无人机机载自动气象站观测结果发现,当风力条件为三级及以下时,反演风速远优于携带传感器观测的风速。
基金This study was co-supported by the National Key Research and Development Program of China(No.2020YFC1512500),The Advanced Aviation Power Innovation institution,The Aero Engine Academy of China,and Tsinghua University Initiative Scientific Research Program,China.
文摘Ducted fans have been extensively used in Unmanned Aerial Vehicles(UAVs)for a variety of missions because of high efficiency,high safety and low noise.Wind,as a kind of typical meteorological condition,brings significant aerodynamic interference to the ducted fan,which seriously threatens flight stability and safety.In this work,the numerical simulation with the Unsteady Reynolds Averaged Navier-Stokes(URANS)method and the sliding mesh technique is performed to evaluate the steady wind effect.The results show that the wind will lead to serious unsteady effects in the flow field,and the thrust fluctuates at the blade passing frequency of 200 Hz.As the wind speed increases,the rotor thrust increases,the duct thrust decreases,and the total thrust changes little.Flow instability may occur when the wind speed exceeds 8 m/s.As the angle of low-speed wind increases,the rotor thrust changes little,the duct thrust increases,and the total thrust increases.In addition,we figure out that cases with the same crosswind ratio are similar in results,and increasing the rotating speed or fan radius is beneficial to performance improvement in wind.The findings are essential to the ducted fan design and UAV flight control design for stable and safe operations in wind conditions.