Uncertainties Of Aerodynamic Coefficients Research Articles

Observer based incremental backstepping terminal sliding-mode control with learning rate for a multi-vectored propeller airship

The problem of finite-time trajectory tracking control for a multivectored propeller airship with model parameter uncertainties and unknown disturbances is addressed in the paper. In order to obtain a fast transient response and finite time convergence without singularity, an incremental backstepping nonsingular terminal sliding mode controller is designed to track desired trajectory within finite time. To overcome the limitation of backstepping terminal sliding-mode control design being dependant on prior knowledge, a nonlinear disturbance-observer is designed to estimate the external observable disturbances. Meanwhile, to reduce system chattering when the tracking error reaches the sliding mode surface, an adaptive learning rate design is proposed for the terminal sliding mode controller such that the tracking error approaches the sliding mode surface at a low speed and so the system chattering is restrained. The closed-loop trajectory tracking control system is proved to be stable and finite time convergence by using Lyapunov theory. The results are compared with traditional backstepping sliding mode control and different learning rate based control design, and they demonstrate the averaged tracking error in altitude and pitch motion is reduced more than 30% by using the disturbance-observer based incremental backstepping terminal sliding mode controller for the multivectored propeller airship to execute a realistic trajectory tracking mission, even in the presence of aerodynamic coefficient uncertainties, unknown disturbances.

Nonsingular Fixed-Time Tracking Guidance for Mars Aerocapture With Neural Compensation

Mars aerocapture is one of the most concerned technologies for future Mars sample-return and manned exploration missions. This article investigates the challenging problem of the reference trajectory tracking guidance for Mars aerocapture under uncertainties. Based on an integral sliding surface, a fixed-time neural adaptive tracking guidance law is synthesized by incorporating the neural network (NN) approximation into the fixed-time integral sliding mode control approach. Benefiting from the integral sliding surface design, the proposed tracking guidance law has no singularity problem inherently existing in terminal sliding mode control. By adopting the NN approximation to compensate for the lumped uncertain term in the feedforward loop, the proposed tracking guidance law is strongly robust against aerodynamic coefficient uncertainties and atmospheric density uncertainty. Stability analysis shows that the radial distance tracking error and its time derivative can stabilize to the small neighborhoods around the origin in fixed time under the proposed tracking guidance law. Finally, the effectiveness and advantages of the proposed tracking guidance law are illustrated through simulations and comparisons.

Neural network adaptive backstepping fault tolerant control for unmanned airships with multi-vectored thrusters

This paper presents the fault tolerant control (FTC) of an unmanned airship with multiple vectored thrusters in the presence of model parameter uncertainties and unknown wind disturbances. A fault tolerant control based on constrained adaptive backstepping (CAB) approach, combined with a radial basis function neural network (RBFNN) approximation, is proposed for the airship with thruster faults. A wind observer is designed to estimate the bounded wind disturbances. An adaptive fault estimator is proposed to estimate the unknown actuator faults. A weighted pseudo inverse based control allocation is incorporated to reconstruct and optimize the practical control inputs of the failed airship under constraints of actuator saturation. Rigorous stability analysis shows that trajectory tracking errors of the airship position and attitude converge to the desired set through Lyapunov theory. Numerical simulations demonstrate the fault tolerant trajectory tracking capability of the proposed NN-CAB controller under the actuator faults, even in the presence of aerodynamic coefficient uncertainties, and unknown wind disturbances.

Backstepping sliding-mode control of stratospheric airships using disturbance-observer

In the presence of unknown disturbances and model parameter uncertainties, this paper develop a nonlinear backstepping sliding-mode controller (BSMC) for trajectory tracking control of a stratospheric airship using a disturbance-observer (DO). Compared with the conventional sliding mode surface (SMS) constructed by a linear combination of the errors, the new SMS manifold is selected as the last back-step error to improve independence of the adjustment of the controller gains. Furthermore, a nonlinear disturbance-observer is designed to process unknown disturbance inputs and improve the BSMC performances. The closed-loop system of trajectory tracking control plant is proved to be globally asymptotically stable by using Lyapunov theory. By comparing with traditional backstepping control and SMC design, the results obtained demonstrate the capacity of the airship to execute a realistic trajectory tracking mission, even in the presence of unknown disturbances, and aerodynamic coefficient uncertainties.

Effects of infrastructure on the aerodynamic performance of a high-speed train

The aerodynamic characteristics of typical high-speed train can be affected by the operating infrastructure, which will affect the flow structure around train body. Five different infrastructure scenarios, including no infrastructure, flat ground, embankment, viaduct and truss bridge, are systemically studied. The purpose is to examine the uncertainties of aerodynamic coefficients caused by the infrastructure. Attention is drawn to variations of aerodynamic coefficients at certain yaw angles caused by the changes in crosswind and train speed. The middle car is chosen for quantifying the effects of five infrastructures by using wind tunnel test and numerical simulations, then followed by a detailed study on aerodynamic characteristics of three cars of train running on viaduct. Pressure distributions are also drawn for a better interpretation. Result shows that the uncertainties in aerodynamic coefficients becomes more obvious as the infrastructure gets complex and yaw angles get bigger. The aerodynamic coefficients of three cars with the viaduct scenario show the similar uncertainties, which are mostly affected by the change in crosswind rather than the train speed.

Control Design for the Autonomous Horizontal Takeoff Phase of the Reusable Launch Vehicles

The control system design for the reusable launch vehicles (RLVs), especially in the autonomous horizontal takeoff phase, is a highly challenging task. Significant issues arise due to the high nonlinearity, large uncertainties of aerodynamic coefficients as well as strong coupling among axes of the airframe. This paper studies autonomous takeoff control problem of the RLVs by the means of trajectory linearization control (TLC) and model predictive control (MPC) theory. The six degree of freedom dynamic model is firstly established, and the flight strategy of takeoff and climb stage is provided through the characteristic analysis of RLVs. Furthermore, the guidance law for the climbing phase is proposed via the TLC method against the high nonlinearity, and a speed based gain-schedule strategy is given under the consideration of both aerodynamic force and friction force. In order to eliminate the ground effect interference, an improved model predictive control approach is presented by introducing the online parameter estimation of the ground effect interaction coefficient, and a coupled model predictive controller is designed by introducing the feedback of sideslip angle into the roll control channel to eliminate the coupling effect. Finally, the performance of the design method for autonomous takeoff control of RLVs is demonstrated through the comparison simulation analysis.

Adaptive sliding-mode-backstepping trajectory tracking control of underactuated airships

The problem of trajectory tracking control for an underactuated stratospheric airship with model parameter uncertainties and wind disturbances is addressed in the paper. An adaptive backstepping sliding-mode controller is designed from the airship nonlinear dynamics model. The proposed controller has a two-level structure for trajectory guidance, tracking and stability, and the developed controller, based on nonlinear adaptive sliding-mode backstepping method, provides airship attitude and velocity control for the entire flight process. Furthermore, an active set based weighted least square algorithm is applied to find the optimal control surface inputs and the thruster commands under constraints of actuator saturation. The closed-loop system of trajectory tracking control plant is proved to be globally asymptotically stable by using Lyapunov theory. By comparing with traditional backstepping control and PID design, the results obtained demonstrate the capacity of the airship to execute a realistic trajectory tracking mission under two cases of lateral- and roll- underactuations, even in the presence of aerodynamic coefficient uncertainties, and wind disturbances.

Fault-tolerant tracking control for a multi-vectored thrust ellipsoidal airship using adaptive integral sliding mode approach

This paper addresses the position and attitude tracking control problem for a recently designed ellipsoidal airship with four vectored thrusters. External disturbances, thruster faults, mass matrix and aerodynamic coefficient uncertainties, which are inevitably encountered in practice, can deteriorate the control system performance of airship and even lead to system instability. To meet these challenges, we develop an adaptive integral sliding mode control method without requiring the prior knowledge of mass matrix and aerodynamic coefficients, in which these uncertainties and faults are considered simultaneously. We showed that the three Cartesian positions and three Euler attitude angles could globally asymptotically track the desired values in the face of external disturbances, thruster faults, mass matrix and aerodynamic coefficient uncertainties. Simulation results validate the effectiveness and advantage of proposed methods.

Uncertainty Identification of Supersonic Wind-Tunnel Testing

In this study, a methodology for the identification of uncertainty of supersonic wind tunnel testing is developed. Instead of conventional multi-tunnel testing, multi-position testing is performed across the characteristic net of supersonic flow. From the variations in aerodynamic coefficients in body axes, the uncertainty caused by flow quality is identified about models of interest. Then, after the consideration of practically independent parameters, uncertainties of aerodynamic coefficients in stability axes are combined. Their validities are confirmed by correlation results of tunnel-to-tunnel comparison tests.

超音速風洞での空力係数の不確かさ

超音速風洞での空力係数の不確かさ

Aeroservoelastic Analysis of Missile Control Surfaces via Robust Control Methods

in this study the effect of uncertainties on the flutter and instability speeds of the control actuation system of a missile is analyzed. The control surface is modeled as a typical section wing with uncertainties in damping and stiffness coefficients. The analyses are carried out for incompressible flow with some uncertainties in aerodynamic coefficients. The actuator dynamics of the aeroservoelastic system is modeled as a second order system with a frequency varying uncertainty.

極超音速風洞での空力係数の不確かさ

In order to estimate the wind tunnel data uncertainty, it is necessary to consider the error propagation caused by the tunnel flow quality. At the NAL 1.27 m hypersonic wind tunnel, multi point calibration tests of the flow field and 6-component force tests of a winged vehicle model were conducted to estimate uncertainties of aerodynamic coefficients. A statistical assessment of Mach number distributions in the uniform core flow gave us an uncertainty of dynamic pressure. Contributions of each uncertainty to the result uncertainties were examined and the large contributions of the dynamic pressure uncertainty were found. These estimated uncertainties were validated by repeat test results and comparisons of the same model test results obtained in another wind tunnel at the same test condition. This uncertainty estimation method is appropriate for hypersonic wind tunnel testing since the model existence gives little effect on the upstream flow.

아음속풍동 시험에서의 불확도 해석

아음속풍동을 이용한 항공기 모델의 공력 측정 시험에 있어 시험 모델의 제작에서부터 자료 획득, 처리 및 표현에 이르는 일련의 모든 과정은 오차를 수반하고 있다. 따라서 시험에서 얻어진 최종적인 공력 결과를 신뢰하고 실제 항공기의 공력 특성으로 사용하기 위해서는 측정결과에 대한 불확도 정도를 알아야 한다. 본 논문에서는 아음속풍동 시험에서 공력 계수 측정에 적용되는 불확도 분석 및 표현 방법에 대하여 나타내었다. Aerodynamic results for an airplane model produced in a subsonic wind tunnel testing inadvertently include errors which are added during model preparation, data acquisition, manipulation, and/or describing the results. Predicting or analyzing uncertainty for the final results is necessary for trusting them and for applying them to real airplane. This paper describes the analytic and systematic method for calculating and describing the uncertainties of aerodynamic coefficients.

Design and flight test of a robust autopilot for the IRIS-T air-to-air missile

The Infra-Red Imaging System-Tail/thrust-vector controlled (IRIS-T) missile is a next-generation short-range air-to-air missile currently developed by Germany, Greece, Italy, Norway, and Sweden. IRIS-T is characterized by an extreme maneuverability for close-in air-to-air combat. The corresponding highly nonlinear and rapidly time-varying dynamics constitute a significant challenge for the autopilot design. Robust control techniques are employed to design lateral and roll controllers taking into account uncertainties in aerodynamic coefficients and actuator bandwidth. The controllers are scheduled as a function of dynamic pressure using a conditioning/blending technique to achieve full flight envelope control capability. The performance and robustness characteristics of the autopilot are assessed in a nonlinear 6 degree-of-freedom simulation and in ground-launched flight tests of the operational missile.

Design and Flight Test of a Robust Autopilot for the IRIS-T Air-To-Air Missile

The IRIS-T missile is a next-generation short range air-to-air missile currently developed by Germany, Canada, Greece, Italy, Norway, and Sweden. IRIS-T is characterized by an extreme maneuverability for close-in air-to-air combat. The corresponding highly nonlinear and rapidly time-varying dynamics constitute a significant challenge for the autopilot design. Robust control techniques arc employed to design lateral and roll controllers taking into account uncertainties in aerodynamic coefficients and actuator bandwidth. The controllers are scheduled as a function of dynamic pressure using a conditioning/blending technique to achieve full flight envelope control capability. The performance and robustness characteristics of the autopilot are assessed in a nonlinear 6 degree-of-freedom simulation and in ground-launched flight tests of the operational missile.

Aircraft Pitch Control via Second-Order Sliding Technique

Control of high-performa nce low-cost unmanned air vehicles involves the problems of incomplete measurements, external disturbances and modeling uncertainties. Sliding mode control combines high precision with robustness to the aforementioned factors. The idea behind this approach is the choice of a particular constraint which, when maintained, will provide the process with the required features and remove, therefore, the plant's uncertainty. However, standard sliding modes are characterized by a high-frequency switching of control, which causes problems in practical applications (so-called chattering effect). A second order sliding controller implemented in the present paper features bounded continuously time-dependent control and provides higher accuracy than the standard sliding mode, while preserving precise constraint fulfillment within a finite time. It possesses, also, significant adaptive properties. The general approach is demonstrated by solving a real-life pitch control problem. Results of a computer simulation and flight tests are presented. I. Introduction Aircraft and missile systems are equipped with control systems whose tasks are to provide stability, disturbance attenuation and reference signal tracking, while their aerodynamic coefficients vary over a wide dynamic range due to large Mach-altitude fluctuations and due to aerodynamic coefficient uncertainties resulting from inaccurate wind tunnel measurements. It is common practice, when designing a control system for an unmanned air vehicle (UAV), to represent the flight envelope by a grid of Mach-altitude operating