Aerodynamic Uncertainties Research Articles

Dynamic surface tracking controller design for a constrained hypersonic vehicle based on disturbance observer

The tracking control problem of a flexible air-breathing hypersonic vehicle subjects to aerodynamic parameter uncertainty and input constraint is investigated by combining nonlinear disturbance observer and dynamic surface control. To design controller simply, a control-oriented model is firstly derived and divided into two subsystems, velocity subsystem and altitude subsystem based on the engineering backgrounds of flexible air-breathing hypersonic vehicle. In every subsystem, compounded disturbances are included to consider aerodynamic uncertainty and the effect of the flexible modes. Then, disturbance observer is not only used to handle the compounded disturbance but also to handle the input constraint, where the estimation error converges to a random small region through appropriately choosing the observer parameters. To sequel, the disturbance observer–based robust control scheme and the disturbance observer-based dynamic surface control scheme are developed for the velocity subsystem and altitude su...

A fast robust guidance scheme for a hypersonic vehicle in the diving phase

A fast robust dive guidance scheme for a hypersonic vehicle is proposed based on the extended state observer and sliding mode observer. The three-degree-of-freedom centroid dynamical and kinematical equations containing model and aerodynamic uncertainties are established. A novel three-dimensional coupling relative dynamical model is described based on exact coordinate transformations. The fast robust dive guidance scheme considering navigation errors and uncertainties is derived with the help of extended state observer and sliding mode observer. An optimal control allocation is adopted and the actual commands of the angle of attack and bank angle are obtained via the second order actuator model. Finally, the performance and robustness of the novel dive guidance scheme is verified and validated via an air-breathing generic hypersonic vehicle.

Adaptive backstepping control for air-breathing hypersonic vehicle with actuator dynamics

This paper investigates the flight longitudinal control problem of a hypersonic vehicle subject to input constraints and aerodynamic uncertainties. A modified control-oriented model is first derived with explicit consideration of the actuator dynamics property. Then, based on the novel dynamics model developed, adaptive backstepping controller and dynamic inverse controller are designed for the altitude subsystem and the velocity subsystem, respectively. To avoid the complexity problem residing in traditional backstepping control caused by the repeated derivations of the virtual control variables, the dynamic surface control technique is involved in conjunction with the backstepping control approach, and a novel second-order sliding-mode-based integral filter instead of the conventional first-order filter is employed. Additionally, in order to deal with actuator magnitude constraints, two auxiliary systems are constructed to generate certain compensating signals to guarantee tracking errors suitable for adaptive parameter estimation. It is proved that the proposed control scheme can guarantee that the tracking errors converge to an arbitrarily small neighborhood around zero in the presence of actuator constraints and aerodynamic uncertainties as well. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed control scheme.

Analytical entry guidance based on pseudo-aerodynamic profiles

An autonomous entry guidance is developed for a hypersonic glide vehicle with high Lift-to-Drag ratio (L/D) based on 3-D analytical glide formulas. To compensate the effects of the Earth's rotation, the pseudo-aerodynamic forces are introduced as the fusions of the aerodynamic forces and inertial forces due to the Earth's rotation. To avoid drastic changes in Angle of Attack (AOA) and bank angle, we carefully forecast the change trends of the inertial forces and then design the pseudo-aerodynamic profiles as inversely proportional functions. Here a complex but useful identity is found and proved theoretically, which helps to simplify the pseudo-aerodynamic profiles without losing accuracy significantly. Subsequently, new 3-D analytical glide formulas are derived for these inversely-proportional profiles and then used to determine the profile parameters and bank reversals. Due to the careful design, the guidance is capable of steering the high-L/D vehicle to any place on the Earth accurately while achieving almost constant commands during the steady glide phase, a major phase of flight. The superior performance of the guidance is verified by the Monte Carlo simulations with challenging disturbances including initial state dispersions, aerodynamic uncertainties, and atmospheric perturbations.

Three-axes predictive control of autopilot for missile

PurposeThe purpose of this paper is to present the autopilot design for the missile under various disturbances.Design/methodology/approachIn this study, model predictive control (MPC) method has been used for autopilot design for each axis. The aim of autopilot is that to keep the roll angle value around the zero degree and to track pitch/yaw acceleration commands. This three-axes control methodology also takes into consideration the interaction between pitch, yaw and roll motions.FindingsThe purpose of using MPC method for three-axes of the autopilot is to decrease the control effort and to make the close-loop system insensitive against modeling uncertainties and stochastic effects.Originality/valueThis study shows that the missile is able to reach to the desired target with good robustness, low control effort and little miss-distance under disturbances such as aerodynamic uncertainties, thrust misalignment and gust affect by using this alternative control method.

Quantification of Airfoil Geometry-Induced Aerodynamic Uncertainties---Comparison of Approaches

Uncertainty quantification in aerodynamic simulations calls for efficient numerical methods since it is computationally expensive, especially for the uncertainties caused by random geometry variations which involve a large number of variables. This paper compares five methods, including quasi-Monte Carlo quadrature, polynomial chaos with coefficients determined by sparse quadrature and gradient-enhanced version of Kriging, radial basis functions and point collocation polynomial chaos, in their efficiency in estimating statistics of aerodynamic performance upon random perturbation to the airfoil geometry which is parameterized by 9 independent Gaussian variables. The results show that gradient-enhanced surrogate methods achieve better accuracy than direct integration methods with the same computational cost.

Adaptive Disturbance-Based High-Order Sliding-Mode Control for Hypersonic-Entry Vehicles

In this paper, an adaptive, disturbance-based sliding-mode controller for hypersonic-entry vehicles is proposed. The scheme is based on high-order sliding-mode theory, and is coupled to an extended sliding-mode observer, able to reconstruct online the disturbances. The result is a numerically stable control scheme, able to adapt online to reduce the error in the presence of multiple uncertainties. The transformation of a high-order sliding-mode technique into an adaptive law by using the extended sliding-mode observer is, together with the multi-input/multi-output formulation for hypersonic-entry vehicles, the main contribution of this paper. The robustness is verified with respect to perturbations in terms of initial conditions, atmospheric density variations, as well as mass and aerodynamic uncertainties. Results show that the approach is valid, leading to an accurate disturbance reconstruction, to a better transient, and to good tracking performance, improved of about 50% in terms of altitude and range errors with respect to the corresponding standard sliding-mode-control approach.

Flight Behavior of an Asymmetric Missile Through Advanced Characterization Techniques

The maneuvers required for guided flight are often obtained through inducing aerodynamic asymmetries. The goal of this study is better understanding of the behavior of asymmetric flight bodies for enhanced control authority and more accurate aerodynamic characterization to improve guidance algorithm design and component (for example, actuator and feedback sensor) selection. The configuration considered is a missile featuring a pair of canards representative of a class of rolling airframes with a single plane of actuating control surfaces. Free-flight experiments are conducted on this body, which demonstrates a means of collecting high-quality experimental data on guided airframes using roll–yaw resonance. Characterization of the asymmetric aerodynamics are obtained from spark range and computational fluid dynamics techniques. Aerodynamic coefficients compare favorably between spark range, computational fluid dynamics, and onboard sensor techniques. Experiments also validate linearized theory of the amplification factor due to roll–yaw resonance. Lastly, the aerodynamic uncertainty quantified during this study enables the maneuverability design margin to be assessed for asymmetric, rolling airframes.

L 1 adaptive control of a generic hypersonic vehicle model with a blended pneumatic and thrust vectoring control strategy

The extreme aeroheating at hypersonic regime and the insufficient dynamic pressure in the near space limit the achievable performance of the hypersonic vehicles using aerosurfaces alone. In this paper, an integrated pneumatic and thrust vectoring control strategy is employed to design a control scheme for the longitudinal dynamics of a hypersonic vehicle model. The methodology reposes upon a division of the model dynamics, and an L1 adaptive control architecture is applied to the design of the inner-loop and outer-loop controllers. Further, a control allocation algorithm is developed to coordinate pneumatic and thrust vectoring control. Simulation results demonstrate that the allocation algorithm is effective in control coordination, and the proposed control scheme achieves excellent tracking performance in spite of aerodynamic uncertainties.

Three-dimensional multivariable integrated guidance and control design for maneuvering targets interception

This paper proposes a new three-dimensional integrated guidance and control (IGC) scheme for intercepting maneuvering targets based on backstepping technique, nonlinear disturbance observer (NDOB) and nonlinear differentiator. To this end, a realistic six degree-of-freedom model, considering aerodynamic uncertainties, cross-coupling effects, model uncertainties and target maneuvers, is constructed first. In order to achieve precise interception, a multivariable NDOB is designed based on second-order sliding mode technique to estimate the lumped uncertainties in finite time. By virtue of the proposed adaptive law, the upper bounds of the lumped uncertainties and their gradients are not required in NDOB design. Using the reconstructed information, a robust IGC law is then synthesized following a backstepping-like way. At each step of backstepping design, a nonlinear differentiator is adopted to avoid analytical differentiation of the virtual control laws and therefore the associated problem of ‘explosion of terms’ is completely addressed. Detailed stability analysis shows that the line-of-sight (LOS) angular rates will converge to zero asymptotically. Finally, the IGC algorithm is tested through numerical simulations against a maneuvering target.

Heavyweight airdrop flight control design using feedback linearization and adaptive sliding mode

This paper investigates the problem of designing a novel adaptive sliding-mode controller for heavyweight airdrop operations. The design objective is to guarantee asymptotic tracking performance of the aircraft states, in the presence of bounded nonlinear uncertainties without prior knowledge of the bounds. On the basis of feedback linearization of the aircraft–cargo model, a sliding-mode control method with projection-based adaptive function approximation is proposed. This method uses an adaptation strategy to achieve robustness against model uncertainties, and a knowledge of the bounds on the complex uncertainties is not required. Notably, the adaptation law with projection can bound the estimated function, and this avoids singularity of the control signal. Simulations are conducted under the condition that one transport aircraft performs a maximum load airdrop mission at a height of 25 m, using single-row single-platform mode. The results verify the good properties of the control method, which can meet the airdrop mission performance indexes well in the presence of ±20% aerodynamic data uncertainty and 20% actuator fault.

Guidance and control system design for hypersonic vehicles in dive phase

A six-degree-of-freedom (6DoF) guidance and control (G&C) scheme for a hypersonic vehicle in the dive phase is proposed in this paper. The 6DoF translational and rotational dynamic and kinematical equations of the hypersonic vehicle are formulated. The intuitive analytical expressions of the 6DoF aerodynamic coefficients of a generic hypersonic vehicle (GHV) are presented. A two-loop control structure is applied for actualizing the 6DoF G&C scheme. The outer loop generates the commands of the angle of attack and the bank angle with the help of the terminal sliding mode control theory and frame system transformation. The inner loop tracks the anticipant Euler angles provided by the outer loop and deduces the required right elevon, left elevon, and rudder fin deflections. Furthermore, the aerodynamic uncertainties and dynamic model uncertainties are accounted for, and extended state observers are employed to estimate these unknown uncertainties. Finally, the effectiveness and robustness of the proposed 6DoF G&C scheme are verified and investigated using the GHV and 6DoF nonlinear simulations.

Study of aerodynamic uncertainty on the complex slender vehicle at high angle of attack

The phenomenon of lateral aerodynamic uncertainty is discovered in the wind tunnel test on the slender vehicle at high angle of attack. To analyze the mechanism of the phenomenon, the numerical simulation method with random pulsation added in the free stream is used, and the aerodynamic uncertainty of the vehicle under the wind tunnel test condition is reproduced by the simulation. The analysis of the flow field leads us to a conclusion that the mechanism of aerodynamic uncertainty is the asymmetry separation, which has a high sensitivity to the disturbance of the flow around the missle. The uncertainty with respect to the angle of attack for a “+” configuration of the main wing is given and the difference of the uncertainty between the “+” and “×” configurations are then analyzed. At last, the action of pulling up through the high angle of attack and the process of temporary atmospheric turbulence are simulated to study the effect of the real flight environment rather than the wind tunnel condition to the aerodynamic uncertainty. Based on these results, it can be concluded that the uncertainty is not looked upon as quite severe in real flight environment as that in the wind tunnel condition, and the maneuverability of flight can be controlled.

Disturbance observer–based dynamic surface control design for a hypersonic vehicle with input constraints and uncertainty

This article presents the flight control problem of a flexible air-breathing hypersonic vehicle under input constraint and aerodynamic uncertainty. First, a control-oriented model is derived and decomposed into velocity subsystem and altitude subsystem, in which compounded disturbances are included to consider aerodynamic uncertainty and the effect of the flexible modes. Second, nonlinear disturbance observer technique is employed to estimate the compounded disturbance, where the estimation error converges to a compact set if the observer design parameters are chosen appropriately. Then, based on disturbance observer, a robust controller and a dynamic surface controller are developed, respectively, for the velocity subsystem and the altitude subsystem. Third, novel robust first-order filters are designed to overcome the “explosion of terms” problem induced by backstepping method. Additional systems are constructed to tackle input constraints. By rigorously Lyapunov stability proof, the designed control strategy can assure that tracking error converges to an arbitrarily small neighborhood around zero. Finally, simulations are performed to show the effectiveness of the presented control strategy.

Multivariate Spline-Based Adaptive Control of High-Performance Aircraft with Aerodynamic Uncertainties

In this paper, a new modular adaptive control system is presented to compensate for aerodynamic uncertainties in high-performance flight control systems. This approach combines nonlinear dynamic inversion with multivariate spline-based adaptive control allocation. A new real-time identification routine for multivariate splines is presented to compensate for aerodynamic uncertainties in the control allocation system. This method, indicated as spline-based adaptive nonlinear dynamic inversion, is applied to control an F-16 aircraft subject to significant aerodynamics uncertainties. Simulation results indicate that the new controller can tune itself each time a model error is detected and has superior adaptability compared to an ordinary polynomial-based adaptive controller. Multivariate splines have sufficient flexibility and approximation power to accurately model nonlinear aerodynamics over the entire flight envelope. As a result, the global model remains intact. Although a part of the model is being reconfigured using incoming observations, the remainder of the model remains unchanged and can be used as an a priori source of information. This prevents the occurrence of sudden fundamental changes in the global model structure, which are experienced when using ordinary polynomials.

Adaptive Multivariable Super-Twisting Sliding Mode Controller and Disturbance Observer Design for Hypersonic Vehicle

A multivariable super-twisting sliding mode controller and disturbance observer with gain adaptation, chattering reduction, and finite time convergence are proposed for a generic hypersonic vehicle where the boundary of aerodynamic uncertainties exists but is unknown. Firstly, an input-output linearization model is constructed for the purpose of controller design. Then, the sliding manifold is designed based on the homogeneity theory. Furthermore, an integrated adaptive multivariable super-twisting sliding mode controller and disturbance observer are designed in order to achieve the tracking for step changes in velocity and altitude. Finally, some simulation results are provided to verify the effectiveness of the proposed method.

302 多項式カオス法を用いた数値流体解析における不確実性の考慮(OS4-1 次世代シミュレーション技術の開拓)

In this research, a polynomial chaos method is utilized for aerodynamic uncertainty analysis of 2D supersonic biplane airfoil. In this method, all uncertain variables / parameters are replaced with a set of orthogonal polynomials, and then governing equations are expanded for each random mode. Finally, uncertainty analysis can be performed efficiently by solving the expanded governing equations directly. The input uncertainties are given on the freestream Mach number and angle of attack as normal distributions. The stochastic distributions of static pressure of the polynomial chaos method show qualitative agreements with full non-linear Monte-Carlo simulation result. The obtained probability density functions of aerodynamic coefficients also show qualitative agreements with that of Monte-Carlo simulation by increasing the order of polynomial chaos.

Mars atmospheric entry trajectory optimization via particle swarm optimization and Gauss pseudo-spectral method

In this paper, a hybrid optimization strategy using particle swarm optimization and Gauss pseudo-spectral method is proposed to generate the optimal entry trajectory of Mars pin-point landing mission. This hybrid optimization strategy merges global optimization with local optimization. Coarse optimization is first conducted to provide a global relative suitable initial guess for subsequent local accurate optimization, which can greatly improve optimization efficiency and robustness and produce the optimal Mars atmospheric entry trajectory from the present position to the designed terminal state satisfying the path constraints. The validity of the hybrid optimization strategy developed in this paper is confirmed by computer simulation in the presence of aerodynamics uncertainties.

Robust Missile Autopilots With Finite‐Time Convergence

AbstractThis paper presents a new longitudinal autopilot to address the finite‐time tracking problem for uncertain agile missiles. The proposed autopilot is essentially a composite control scheme, which is obtained through the finite‐time control methodology and the nonlinear disturbance observer (NDOB) approach. The key idea in this scheme is that the NDOB is adopted to estimate the aerodynamic uncertainties and external disturbances in an integrated manner. With the aid of the finite‐time bounded function and the Lyapunov function method, the finite‐time stability of the closed‐loop system is established, which shows that the angle‐of‐attack response will converge to the external command signal in finite time. Numerical simulation results are presented to demonstrate the superiority of the proposed scheme.

High angle of attack command generation technique and tracking control for agile missiles

This paper proposes a new tracking control design for agile missiles at high angle of attack regime. Firstly, mathematical descriptions of the problem are presented, taking aerodynamic uncertainties into consideration. Based on the dynamics inverse modeling in a neural network (NN) architecture, the angle of attack command augmented by a variable structure technique is then generated to correspond with the desired turn rate. Subsequently, a nonlinear adaptive control approach using sliding mode control (SMC) technique is employed to track the angle of attack command. Due to the introduction of extended state observer (ESO), the proposed approach is able to online estimate the system uncertainties and calculate derivatives of signals required for composing the control law. Finally, to demonstrate the feasibility and validity of the proposed methodology, the numerical simulation of the agile missile intercepting a target in the rear hemisphere is presented.