Benchmark Active Controls Technology Research Articles

Design of an Active Disturbance Rejection Control for Transonic Flutter Suppression

Conventional controls, such as an optimal control with a notch filter, are able to remove the flutter instability under subsonic flows but may need higher adaptability to make the controllers stable under transonic flows with oscillating shocks, especially for the wing model with parameter uncertainties. In this paper, an error-based control law designed via the active disturbance rejection control algorithm is proposed for the transonic flutter suppression of a wing model with parameter uncertainties and measurement noises taken into account. With the proposed control law, the observed output signal and its time derivative, the unmodeled dynamics, and the measurement noises are consistently estimated. The observed output signal and its time derivative are used to design a feedback control law for adjusting the output errors, whereas the observed unmodeled dynamics and the measurement noises are used to guarantee the adaptability and anti-interference of the proposed controller. To demonstrate the control performances, the wing of benchmark active control technology is studied for the transonic flutter suppression. The numerical results show that the present control law can effectively suppress the transonic flutter at a wide range of Mach numbers and has noticeable adaptability to the variation in stiffness parameters.

The interaction between flutter and buffet in transonic flow

This paper presents a kind of nodal-shaped oscillation that is caused by the interaction between flutter and buffet in transonic flow. This response differs from the common limit cycle oscillation that appears in transonic aeroelastic problems. The benchmark active controls technology model with the NACA0012 airfoil is used as the research model. First, both buffet and flutter cases are computed through unsteady Reynolds-averaged Navier–Stokes method and are validated by experimental data. Second, the interaction is found to occur beyond the flutter onset velocity at Mach 0.71. When the pitching angle of a fluttering structure exceeds the buffet onset angle, the high-frequency aerodynamic loads induced by transonic buffet destroy the original flutter model, and then the amplitude of the structure motion decays. When the structural pitching angle is less than the buffet onset angle, the buffet disappears and flutter occurs again. As the process repeats itself, the transonic aeroelastic system displays a nodal-shaped oscillation (divergent–damping–divergent–damping oscillation). Finally, the mechanism of the interaction is discussed by analyzing the energy transportation between the flow and the structure in one cycle of nodal-shaped oscillation, and by observing the variation in the phase-angle difference between the plunging and pitching displacements. In this way, this research provides a new approach to understand flutter suppression.

Open/Closed-Loop Aeroservoelastic Predictions via Nonlinear, Reduced-Order Aerodynamic Models

Recently, the parallel cascade reduced-order modeling approach has been successfully used for the flutter prediction of a two-degree-of-freedom wing section. However, this approach has been less successful when applied to reveal other important aeroelastic phenomena, such as the transonic aeroservoelastic behaviors of a three-dimensional wing with a trailing-edge control surface. Because of the complexity introduced by the forced control-surface deflection, effects of oscillating shock waves, and aerodynamic viscosity, the stability of the dynamic linear parts of the parallel cascade reduced-order model cannot be guaranteed. In this paper, a novel, stable representation of the parallel cascade reduced-order model is explored in which the linear part is identified by using a predictor-based subspace scheme. To demonstrate the performance of the present parallel cascade reduced-order model in modeling the aeroservoelastic behaviors of a three-dimensional wing with a trailing-edge control surface, the Benchmark Active Control Technology wing is used as an illustrative example. The numerical results demonstrate that the parallel cascade reduced-order models are capable of modeling open/closed-loop aeroservoelastic behaviors. Moreover, the effects of the aerodynamic nonlinearity on the dynamic behaviors of the aeroservoelastic systems are investigated always based on the proposed reduced-order model.

Robust Generalized Predictive Control with Uncertainty Quantification

DOI: 10.2514/1.54510 This paper presents a robust predictive control method with uncertainty quantification for problems, such as online aircraft flutter suppression. The proposed approach begins by identifying the multistep output prediction matrices under various test conditions from online time-domain input/output data. Singular value decomposition is then used to characterize and quantify the parameter uncertainties of the prediction matrices. The predicted responseerrorduetoparameteruncertaintiesisintegrated intothepredictivecontroldesignprocessforrobustness. The proposed method provides an innovative and efficient way to incorporate the quantified uncertainty in predictive control design with a linear process. The proposed approach is demonstrated by application to the Benchmark Active Controls Technology wind-tunnel model.

Output Regulation with Actuator Saturation for the Benchmark Active Control Technology Model

Output Regulation with Actuator Saturation for the Benchmark Active Control Technology Model

A novel model reduction method based on balanced truncation

The main goal of this paper is to construct an efficient reduced-order model (ROM) for unsteady aerodynamic force modeling. Balanced truncation (BT) is presented to address the problem. For conventional BT method, it is necessary to compute exact controllability and observability grammians. Although it is relatively straightforward to compute these matrices in a control setting where the system order is moderate, the technique does not extend easily to high order systems. In response to the challenge, snapshots-BT (S-BT) method is introduced for high order system ROM construction. The outline idea of the S-BT method is that snapshots of primary and dual system approximate the controllability and observability matrices in the frequency domain. The method has been demonstrated for 3 high order systems: (1) unsteady motion of a two-dimensional airfoil in response to gust, (2) AGARD 445.6 wing aeroelastic system, and (3) BACT (benchmark active control technology) standard aeroservoelastic system. All the results indicate that S-BT based ROM is efficient and accurate enough to provide a powerful tool for unsteady aerodynamic force modeling.

Control of an Aeroelastic System with Actuator Saturation

The objective of this study is the semiglobal stabilization of the benchmark active control technology wind-tunnel model developed by NASA Langley Research Center. This study applies established theoretical results to the design of a saturation linear state feedback control law. The framework of this investigation is the construction of the null-controllable region and domains of attraction of the planar antistable subsystem of the higher order model in its canonical modal form. Numerical simulations at different densities of the unstable wind-tunnel system are presented that demonstrate construction and performance of the control law applied to an a priori defined subset of the null-controllable region.

Wing flutter suppression enhancement using a well-suited active control model

State-space theory is employed here to model a new active wing flutter suppression control. In this paper, the design of a flutter suppression control law, for the NASA Benchmark Active Control Technology wing, is proposed through a single input-single output controller and unsteady aerodynamics is modelled using the Theodorsen's theory. Wing dynamic model is obtained by combining the aeroelastic equations of motion with the actuator model presented. Open-loop dynamic behaviour is examined for a single feedback variable that combines pitch and plunge accelerations. Here, a new formulation of control law, based on classical control techniques and featuring two feedback closed-loops, is successfully employed to reach superior stability robustness with respect to other control laws designed with classical flutter suppression schemes having only one feedback closed-loop. The process allows the stability of the aeroelastic system for flight speeds that exceed the open-loop flutter velocity.

Control law design for transonic aeroservoelasticity

Existing computational transonic aeroservoelastic researches focus on directly coupling the structural dynamic equations, CFD solver and servo system in time domain, study the effect of the given feedback control laws on the responses of the aeroelastic system. These works have not involved the design of the flutter active control law. The non-linearity of transonic flow brings great difficulties to aeroservoelastic analysis and design. Recent research of the unsteady aerodynamic reduced order models (ROM) based on CFD provides a challenging approach for transonic aeroservoelastic analysis and design. Coupling the structural state equations with the aerodynamic state equations of the wing and the control surface based on the ROM, we construct a transonic aeroservoelastic model in state-space. Then the sub-optimal control method based on output feedback is used to design the flutter suppressing law. The study first demonstrates the open loop of the Benchmark Active Controls Technology (BACT) wing. The computational results of the CFD direct simulation method and the ROM analysis method are both agree well with the experimental data. Then both the closed loop time responses and the flutter results by ROM technique are compared with those of numerical aeroservoelastic simulation based on Euler codes to validate the correctness of the design method of the control law and aeroservoelastic analysis method. An increase of up to 20% of the speed index can be achieved by the control law designed by sub-optimal control method for this model.

Global Robust Control of an Aeroelastic System Using Output Feedback

A EROELASTIC systems exhibit a variety of phenomena including instability, limit cycle, and even chaotic vibration. Researchers in aerodynamics, structures, materials, and control have made interesting contributions to the analysis and control of aeroelastic systems [1]. Readers may refer to an excellent article by Mukhopadhyay [2] for the analysis and control of aeroelastic systems. A benchmark active control technology (BACT) windtunnel model has been designed at the NASA Langley Research Center and control algorithms for flutter suppression have been developed [3–5]. At Texas A&Ma 2-degrees-of-freedom aeroelastic model has been developed and tests have been performed in a wind tunnel to examine the effect of nonlinear structural stiffness, and control systems have been designed using linear control theory, feedback linearizing technique, and adaptive control strategies [6– 10]. Based on the Euler–Lagrange theory, control of an aeroelastic model has been considered [11]. The state variable and output feedback designs of [8–10] are based on adaptive control techniques. The synthesis of adaptive controllers is not simple because a large number of parameters must be updated in the dynamic feedback loop. It is also well known that unmodeled dynamics of the system can cause parameter divergence and instability in the closed-loop system. Therefore, it is interesting to design nonadaptive control systems for uncertain aeroelastic models which can be synthesized relatively easily. The contribution of this paper lies in the design of a robust control system for the global regulation of an aeroelastic system which describes the plunge and pitch motion of a wing. The model has polynomial type structural nonlinearity and only the pitch angle is measured for feedback. It is assumed that all the system parameters are unknown to the designer, but the bounds on uncertainties are known. For the purpose of design, afirst-order dynamic compensator is introduced and a “chained” structure of the aeroelastic model including the dynamic compensator is obtained by an appropriate coordinate transformation. Then using the Lyapunov stability theory, a control law for robust output regulation of the transformed system including the compensator is derived. In the closed-loop system, the controller accomplishes global robust stabilization of the aeroelastic system and system trajectories converge to the origin. Simulation results for various flow velocities and elastic axis locations are obtainedwhich show that the control system is effective in flutter suppression in spite of the large parameter uncertainties. An attractive feature of this control system lies in its simplicity from the point of view of implementation.

Robust Multivariable Flutter Suppression for Benchmark Active Control Technology Wind-Tunnel Model

The Benchmark Active Controls Technology (BACT) project is part of NASA Langley Research Center''s Benchmark Models Program for studying transonic aeroelastic phenomena. In January of 1996 the BACT wind-tunnel model was used to successfully demonstrate the application of robust multivariable control design methods (H infinity and mu-synthesis) to flutter suppression. This paper addresses the design and experimental evaluation of robust multivariable flutter suppression control laws with particular attention paid to the degree to which stability and performance robustness was achieved.

Comparison of Two Navier-Stokes Methods with Benchmark Active Control Technology Experiments

Two commonly used three-dimensional compressible Navier-Stokes codes are applied to select test cases from an experimental data set on a model known as the Benchmark Active Control Technology (BACT) wing. The BACT test provides data for the validation of aerodynamic, aeroelastic, and active aeroelastic control simulation codes. An overview will be presented of the two Navier-Stokes aeroelastic codes currently being used in an analysis of that data. A collection of results obtained by the two methods will be compared with the BACT experimental data for a wing with a statically deflected spoiler and statically and dynamically deflected aileron. Both methods employ structured computational fluid dynamics flow solvers and continuous surface modeling for the computation of complex moving control surface geometry. Motivation for this work is the development of an integrated computational aeroelasticity and active control simulation capability for the transonic flight regime and validation of that capability using the BACT wing data.

Control of a Nonlinear Aeroelastic System Using Euler-Lagrange Theory

Active control of nonlinear aeroservoelastic (NL-ASE) systems is a key technology for future aircraft development. Because of the large number of nonlinear behaviors exhibited by NL-ASE systems, issues of local Lyapunov stability and structural stability must be addressed in controller design. A design methodology based on an ASE system being governed by the Euler-Lagrange (EL) equations is presented. The controller design procedure involves shaping the Lagrangian to a desired form and providing channels to dissipate energy. We consider EL systems with arbitrary Lagrangians and give sufficient conditions for local asymptotic stability and passivity. Parameter-dependent controllers are developed for large-scale changes in operating conditions and transitions across bifurcations. A procedure to design stabilizing controllers that are themselves Lyapunov and structurally stable is also given. The techniques are applied to a nonlinear version of benchmark active control technology wind-tunnel model that exhibits a Hopf bifurcation leading to flutter. Numerical results showing local asymptotic stability and structural stability for large-scale dynamic pressure variations across bifurcations are presented.

Mapping of Frequency Response Performance Specifications Into Parameter Space

A procedure is presented that enables frequency response performance specifications (e.g. magnitude, phase, sensitivity, H∞, etc.) to be mapped directly into parameter space. This procedure significantly enhances the versatility of parameter space techniques by facilitating the design and analysis for systems with both structured and unstructured uncertainty. For analysis, the procedure can be used to immediately show at which operating conditions the system provides the desired performance. For control design, the simplicity and transparency attributed to parameter space techniques are retained, while ensuring that the additional frequency domain specifications are also satisfied. This new procedure is demonstrated by designing a flutter suppression controller for NASA Langley’s Benchmark Active Controls Technology (BACT) wing flutter model. The control design example incorporates both eigenvalue specifications and frequency response magnitude specifications.

Comparing Linear Parameter-Varying Gain-Scheduled Control Techniques for Active Flutter Suppression

Two linear parameter-varying gain-scheduled controllers for active e utter suppression of the NASA Langley Research Center’ s Benchmark Active Control Technology (BACT) wing section are presented and compared to a previously presented gain-scheduled controller. The BACT wing section changes signie cantly as a function of Mach and dynamic pressure. The two linear parameter-varying (LPV) gain-scheduled controllers incorporate these changes as well as bounds on the rate of change of Mach and dynamic pressure. The inclusion of rate bounds in the design process allows for improved performance over a larger range of operating conditions than previously achieved by a linear fractional transformation gain-scheduled controller. The LPV controllers differ in that one primarily reduces coupling between the trailing-edge e ap and the pitch and plunge modes, whereas the second optimizes wind gust attenuation. Closed-loop stability and improved performance are demonstrated via time simulations in which both Mach and dynamic pressure are allowed to vary in the presence of a Dryden wind-gust disturbance.

Benchmark Active Controls Technology Model Aerodynamic Data

The Benchmark Active Controls Technology (BACT) model is a part of the Benchmark Models Program (BMP). The BMP is a NASA Langley Research Center program that includes a series of models which were used to study different aeroelastic phenomena and to validate computational fluid dynamics codes. The primary objective of BACT testing was to obtain steady and unsteady loads, accelerations, and aerodynamic pressures due to control surface activity in order to calibrate unsteady CFD codes and active control design tools. Three wind-tunnel tests in the Transonic Dynamics Tunnel (TDT) have been completed. The first and parts of the second and third tests focused on collecting open-loop data to define the model''s aeroservoelastic characteristics, including the flutter boundary across the Mach range. It is this data that is being presented in this paper. An extensive database of over 3000 data sets was obtained. This database includes steady and unsteady control surface effectiveness data, including pressure distributions, control surface hinge moments, and overall model loads due to deflections of a trailing edge control surface and upper and lower surface spoilers.

Passivity-Based Robust Control with Application to Benchmark Active Controls Technology Wing

A passivity-based robust control design methodology is presented. A brief review of the stability results is given for passive linear and nonlinear systems followed by four different passie cation methods for rendering nonpassive systems passive. The robust control methodology via robust passie cation is demonstrated by application to the Benchmark Active Controls Technology subsonic wing. The controller design is shown to provide robust stability and satisfactory performance.

Computational Test Cases for the Benchmark Active Controls Model

Unsteady aerodynamic and aeroelastic computational test cases have been selected from the data set for the Benchmark Active Controls Technology model. Data sets for trailing-edge control surface oscillations and uppersurfacespoileroscillationsforarangeofMachnumbers, angleofattack, andstaticcontroldee ectionsareincluded. Cases also include static angles of attack, static trailing-edge control, and static upper-surface spoiler dee ections for a range of conditions near those for the oscillation cases. The aeroelastic test cases include three types of e utter instability and dynamic response measurements for oscillations of the controls on the e exible mount.

Transonic Flutter Suppression Control Law Design and Wind-Tunnel Test Results

Fluttersuppressioncontrollawdesignandwind-tunneltestresultsintransonice owforaNACA0012wingmodel, under the benchmark active control technology program at NASA Langley Research Center, will be presented. Two control law design processes using classical and minimax techniques are described. Design considerations for improving the multivariable system robustness are outlined. The classical control law was digitally implemented and tested in the NASA Langley Transonic Dynamics Tunnel. In wind-tunnel tests in air and heavy gas medium, the closed-loop e utter dynamic pressure was increased by over 50% up to the wind-tunnel upper limit. The active e utter suppression system also provided signie cant robustness, relative to gain and phase perturbations, even in the presence of transonic shocks and e ow separation.