Flutter Suppression System Research Articles

Stochastic robustness analysis of wing-aileron flutter suppression systems

In this work a stochastic robustness analysis approach is used to compare the performances of two non-linear flutter suppression systems designed for stabilization of a wing-aileron lifting structure. A reduced order modelling approach based on an alternative aeroelastic beam finite element is presented and used for the flutter suppression systems design, which are driven by a simple adaptive controller and a sliding mode controller, respectively. A heuristic algorithm is used to determine the simple adaptive controller invariant parameters at the design point while a simple parametric study is performed to tune the sliding mode controller. The performances of each closed loop system are evaluated taking into account mass, stiffnesses, and aerodynamics uncertainties of the aeroelastic plant also considering the presence of discrete gust disturbances.

Simple adaptive wing-aileron flutter suppression system

In this work a simple adaptive flutter suppression system is designed in order to increase the operative speed range of a wing-aileron aeroelastic plant. The equivalent beam finite element based aeroelastic modeling of a wing equipped with a trailing edge aileron in incompressible flow is presented and its state space representation is provided. The almost strictly passivity of the plant is assured by means of a parallel feed-forward compensator implementation and the invariant controller parameters are tuned using a population decline swarm optimization algorithm that minimize the integral of the time absolute error on the wing tip torsion angle. The performance of the closed loop system are studied carrying out numerical simulations that reproduce different flight scenarios with the presence of speed variations, disturbances, and gusts proving the effectiveness of the proposed simple adaptive flutter suppression architecture.

Stochastic aeroservoelastic analysis of a flapped airfoil

In order to increase the operability range of wings in terms of speed, the suppression of aeroelastic vibrations due to flutter phenomena using a trailing edge flap is analyzed. The aeroelastic modelling of a three degrees of freedom 3DOF airfoil in unsteady incompressible flow with pitch and control surface stiffness non-linearities is studied and an augmented state space representation is used for the time domain analysis of the problem. A V-stack piezoelectric actuator is used to move the trailing edge flap and its dynamic behavior is included in the analyses by means of a finite element model; the actuator input voltage saturation is also taken into account. A heuristic method, named Population Decline Swarm Optimization, is used for the tuning of the filtered PID controller parameters for different velocity values. The optimization algorithm is also used for the tuning of the Simple Adaptive Controller SAC invariant gains. A general uncertain state space modelling of the aero-servo-elastic plant is provided and used first for the open loop stochastic flutter analysis. Then, the stochastic robustness analysis is carried out to verify the robustness to structural, aerodynamic, and actuator parameters uncertainties of the proposed flutter suppression systems and to compare the gain scheduled PID approach with the SAC scheme.

Simple adaptive V-stack piezoelectric based airfoil flutter suppression system

The suppression of aeroelastic vibrations due to flutter using a trailing edge flap is analyzed to increase the speed operability range of wings. The aeroelastic model of a 3DOF airfoil in incompressible flow is presented and an augmented state-space representation is used for the time domain analysis. A finite element model of a V-stack piezoelectric actuator, used to move the trailing edge flap, is introduced to model the actuator dynamics. The use of the simple adaptive controller is investigated to realize an adaptive flutter suppression system. A parallel feedforward compensator is tuned to make the plant almost strictly passive and a metaheuristic algorithm is used to determine the invariant parameters. Numerical simulations are carried out to verify the performance of the simple adaptive flutter suppression system in presence of speed variations and disturbances. Numerical results proved that the SAC flutter suppression system improves the closed loop system flutter boundary with respect to a gain scheduled PID controller.

Synthesis of an active flutter suppression system in the transonic domain using a computational model

ABSTRACTControl laws for implementing active flutter suppression are generally derived from linear aeroelastic models. In this paper, families of control laws for implementing an active flutter suppression system were initially designed using linearised aeroelastic models based on the doublet lattice method after ignoring the aerodynamic loads associated with relatively faster time scales. Using these preliminary sets of control laws and the nonlinear transonic small disturbance theory, near-optimum control laws were chosen in the transonic domain to maximally increase the flutter speed of a typical aircraft wing by at least 16% or more. Thus it is shown that it is feasible to systematically design near-optimal control laws for active flutter suppression using computational models in transonic flow. The doublet lattice method coupled with the zeroth-order matrix Padé approximant provided the fastest method for synthesising a large number of preliminary control laws. The methodology was successfully demonstrated by applying it to two benchmarking examples.

Analysis of dynamic response and flutter suppression system effectiveness of a long-haul aircraft in transonic flight mode

Analysis of dynamic response and flutter suppression system effectiveness of a long-haul aircraft in transonic flight mode

Hypersonic flutter and flutter suppression system of a wind tunnel model

The aeroelastic behavior of a thin flat rudder model was numerically simulated and experimentally investigated in a hypersonic wind tunnel. In particular, a flutter suppression system taking advantage of collision within small gaps was proposed and a novel system for the flutter simulation of the whole nonlinear aeroelastic system including the flutter suppression system was developed. First, the critical flutter dynamic pressure of the rudder without the flutter suppression system was calculated with different methods. Then, the whole nonlinear aeroelastic system, including the flutter suppression system, was simulated to design the gap size. Finally, the flutter suppression system was experimentally validated in a hypersonic wind tunnel operating at Mach number 5. The typical phenomenon of Limit Cycle Oscillation (LCO) was observed, avoiding the structural failure of the model and the consistency between numerical and experimental results was demonstrated. The proposed suppression system can improve the design and reusability of test models of hypersonic flutter experiments.

Delayed sub-optimal control for active flutter suppression of a three-dimensional wing

In this paper, delayed sub-optimal control based on partial-state feedback for flutter suppression system involving time-delay is investigated, and the effectiveness of the sub-optimal controller is compared with the optimal controller based on full-state feedback. Firstly, the aeroservoelastic (ASE) model of the flexible wing with control surfaces is given, and the method to dispose the time-delay in the control input is introduced. Then, the determination of the importance of each state in control feedback is studied using the second-order sensitivity of the performance index with respect to the control gain. Finally, the effectiveness of sub-optimal controller is compared with optimal controller through numerical simulations. Simulation results show that the importance of states can be effectively determined by the second-order sensitivity, and the delayed sub-optimal controller can achieve a control effect quite close to the delayed optimal controller. The order of the delayed suboptimal controller designed in this paper is lower, so it shows more engineering significance.

Time-Domain Aeroservoelastic Modeling and Active Flutter Suppression by Model Predictive Control

A time-domain aeroservoelastic model is developed to calculate the flutter speed and an active flutter suppression system is designed by model predictive control. Thefinite-state, induced-flow theoryandequilibrium beam finite elementmethod are chosen to formulate the aeroservoelastic governing equations in state-space form, which is necessary for active flutter suppression design with modern control theory. A sensitivity analysis is performed to find the most appropriate number of induced-flow terms and beam elements. Model predictive control theory is adopted to design an active flutter suppression system due to its ability to deal with the constraints on rate change and amplitude of input. The numerical result shows a satisfactory precision of the flutter speed prediction, the close loop analysis shows that the flutter boundary is considerable expanded.

슬라이딩 모드 제어기법을 이용한 유연날개의 플러터 억제

This paper presents the design of an active flutter suppression system for flexible wing using sliding mode control method. The aerodynamic force generated by the motion of a flexible wing control surface is utilized as control force. For this purpose, aeroservoelastic model is formulated by blending aeroelastic model, control surface actuator model, and gust model. A sliding mode controller is designed for active flutter suppression on the aeroservoelastic model in conjunction with Kalman filter that estimates the system states based on the measured output. The performance of the designed controller is demonstrated via numerical simulation for the representative flexible wing model.

Group Delay in Digital Filter Induced Instability of a Two-Dimensional Airfoil Active Flutter Suppression System

The presented paper deals with the group delay in the digital filter induced instability of a two dimensional airfoil section active flutter suppression system. Firstly, the aeroelastic model of the airfoil with an ultrasonic motor actuated control surface is set up; secondly, both H∞and μ robust controllers are designed; and then, the group delay induced instability in wind tunnel test is presented; finally, through a combined theoretical and numerical study, the test phenomenon is well explained. Wind tunnel experiments and numerical simulations demonstrate that long enough group delay in digital filter can induce instability of flutter control system, the flutter under control will decrease first, and then become another flutter of lower frequency and moderated amplitude, and μ controller works better than H∞controller on the same condition.

Stability of a time-delayed aeroelastic system with a control surface

This paper investigates the effects of time delay on the flutter instability of an actively controlled airfoil in an incompressible flow field. Firstly, in view of the presence of time delays in the actual control system, multiple time delays in feedback loop are introduced to the present flutter suppression system. Next, the stability boundaries of the closed-loop system with multiple time delays are obtained by solving a polynomial eigenvalue problem, and are validated by numerical simulations. The results demonstrate that time delays in control loop have strong effects on the stability of controlled aeroelastic systems and should not be ignored in the design of the aeroservoelastic system of the aircraft.

Active Flutter Suppression for a Three-Surface Transport Aircraft by Recurrent Neural Networks

approach for the design of a flutter suppression system by means of Recurrent Neural Networks (RNNs). The controller is used to move flutter instabilities outside the flight envelope of an unconventional three surface, transport aircraft configuration. The design process requires a comprehensive aircraft model, where flight mechanics, structural dynamics, unsteady aerodynamics and control surface actuators are represented in state-space form, according to the “modern” aeroelastic approach. The control system implemented for flutter suppression is based on two RNNs: one is trained to identify system dynamics; the other works as a controller using an indirect inversion of the identified model. Keeping the training of both RNNs “on line” leads to an adaptive control system. Extensive numerical tests are used to tune the neural network design parameters and to show how the neural controller increases system damping, widening the flutter-free flight envelope by more than 15% of the uncontrolled flutter velocity. lutter can often be a critical problem for current flight vehicle design, due to the increase of structure lightness which leads to high structural flexibility. Several approaches may be followed to solve this problem. The first, which may be denominated “passive”, basically goes through a re-design of the aircraft to increase its stability boundaries. The second, which may be called “active”, tries to exploit the capabilities of control systems to improve aircraft stability properties, usually with a smaller weight increment. Furthermore, such controllers can be used to improve the performances and the cruise comfort. Here, an active control strategy based on Recurrent Neural Networks (RNNs) for flutter suppression is designed to improve the stability boundaries and performances of a transport aircraft with an unconventional configuration, denominated X-DIA. The X-DIA, sketched in figure 1, is a conceptual design of a short range 70-seats jet liner based on the idea of using three main lifting surfaces: a front canard, a 15 deg. forward swept wing and a T-tail. The rear location of the main wing along the fuselage, allowed by the forward swept wing coupled with the canard surfaces, is expected to yield a positive cooperation between structures and aerodynamics, allowing a significant weight saving and drag reduction. This configuration is currently the object of numerous investigations at the Dept. of Aerospace Engineering of Politecnico di Milano (DIAPM), both numerical and experimental. 1‐3 A 1/10, Froude scaled, wind tunnel model has been built and tests

Application of Fiber Optic Sensor and Piezoelectric Actuator to Flutter Suppression

Introduction F OR lightweight and flexible structures, it is important to measure and suppress the flow-induced vibrations caused by interactions between fluid and structures. Dynamic aeroelastic instabilities, such as flutter, involve the interaction of aerodynamic, inertia, and elastic forces of flight structures. Because flutter may cause disastrous structural failures in flight, the prediction of stability boundary and the suppression of flutter are very important analysis issues for flight structures. In recent years, several active control strategies have been studied to modify favorably the behavior of aeroelastic systems using smart material and structure technologies. Lazarus et al.1 successfully applied multi-input/multi-output controls to suppress vibration and flutter of a platelike lifting surface with surface-bonded piezoelectric actuators. Han et al.2 performed numerical and experimental investigation on active flutter suppression of a swept-back cantilevered plate. Application of piezoelectric actuation to flutter control of a more realistic wing model was achieved under the Piezoelectric Aeroelastic Response Tailoring Investigation program at NASA Langley Research Center.3 Recently, fiber bragg grating (FBG) sensors have been increasingly studied for a variety of applications: health monitoring, vibration measurement, nondestructive testing and so on. Gratings are simple, intrinsic sensing elements that can be photoinscribed into a silica fiber and have the same advantages normally attributed to fiber sensors. In addition, the devices have an inherent self-referencing capability and are easily multiplexed in a serial fashion along a single fiber.4 An overview of FBG sensors and systems is presented in Ref. 4. This paper investigates dynamic application of an FBG sensor system to the flutter suppression of a composite plate structure. In practical situations, the modeling of an aeroelastic system is complicated and the dynamic characteristics of an aeroelastic system changes with respect to the airflow speed. Therefore, the adaptiveness and the robustness are key features for an aeroelastic control system. A neuroadaptive feedback control algorithm is used in this study. The control system consists of the neuroidentification model and the neurocontroller. The real-time implementation of the adaptive controller is performed using a digital signal processing (DSP) board. The effectiveness of the flutter suppression system is evaluated via wind-tunnel testing.

Design and test of a multi‐input multi‐output adaptive active flutter suppression system based on neural network for a wing model

AbstractThis paper describes the application of a recurrent dynamic neural network to the problem of adaptive active flutter suppression. A significant feature of the neural controller is its application to an unstable and non‐minimum phase system. The development of the system and its experimental verification are carried out on a wing model with two control surfaces, one on the leading and one at the trailing edge, and two accelerometers. The controller combines a first network for the identification of the variables to be controlled, i.e. the two wing tip accelerations at the leading and trailing edge, with a second network, that commands the deflection required to the control surfaces. It is used for the control task using the output generated by the first network. Adaptivity is obtained by maintaining an on‐line training on both of the neural networks. Extensive preliminary numerical simulations have permitted the authors to define the values of the design parameters aimed at the achievement of an optimal compromise between computational requirements and system performances. The results of the application to the real wing model have shown the effectiveness of such a controller in adapting to different operational conditions, extending flutter free envelope of the wing model up to a speed 30% higher than the uncontrolled flutter onset.

Active Control of Store-Induced Flutter in Incompressible Flow

An active method for enhancing the performance and improving the robustness of a decoupler pylon-mounted store flutter suppression system is presented. The proposed active decoupler pylon involves the use of a piezoceramic wafer strut as an actuator that acts as a soft spring between the wing and the store. A two degree-of-freedom typical section of an airfoil is used to represent the structural model of the wing. The circulatory component of the incompressible aerodynamic loads is modeled using an approximation to the Theodorsen function. The GBU-8/B store configuration of an F-16 aircraft is used for the analysis. A classical robust control algorithm called the loop transfer recovery method is applied to design a controller for the linear wing/store model. Some simulations are presented using singular-value Bode plots for robust stability and nominal performance analysis.

Multi-Input/Multi-Output Adaptive Active Flutter Suppression for a Wing Model

The work develops and verifies experimentally a multi-input/multi-output adaptive active flutter suppression system for a built-up wing model fitted with a leading- and a trailing-edge control surface and two accelerometers. An indirect adaptive scheme, combining an identification of a discrete dynamic model followed by the design of a stabilizing control law, has been used. The identification is based on a recursive multivariable-extended least-squares approach applied to the input/output relations connecting the accelerometer signals to the control surfaces deflections, while the stabilizing controller is designed by a full-state eigenstructure assignment method. The order and structure of the control system and the tuning of its design parameters have been carried out through extensive numerical simulations aimed at the determination of an optimal compromise between system performances and computational requirements. The adaptive controller thus obtained was implemented on a wing model and tested in a wind tunnel by using two loosely coupled cooperating personal computers, one for the position servos of the control surfaces, the other for the indirect adaptive flutter suppression. The tests have demonstrated that the system is capable of achieving a significant increase of the subcritical aeroelastic damping and of the flutter speed of the wing model.

H∞ control for flutter suppression of a laminated plate with self-sensing actuators

Active flutter suppression system of a composite plate wing model is designed using a reduced order model. The analysis for a laminated composite wing with segmented piezoelectric sensor/actuator pairs is conducted by the Ritz solution technique. Unsteady aerodynamic forces calculated by doublet lattice method are approximated as the transfer functions of the Laplace variable by the minimum state method. Among the aerodynamic states obtained from rational function approximation, only one aerodynamic state is included in the plant model for feedback purpose. The neglected aerodynamic states are regarded as modeling error. The control system uses the integrated and collocated piezoelectric self-sensing actuator pairs so as to prohibit the non-minimum phase model and the spillover due to the unmodeled dynamics. Based on the mixed-sensitivityH∞ control method, the control parameters are determined. Using a simple wing model, the performance of the controlled system is shown in the frequency and time domain respectively. The electric current and the power requirement for aeroelastic control are also predicted.

Optimal design of composite lifting surface for flutter suppression with piezoelectric actuators

This paper presents the optimal design of an active flutter suppression system for an adaptive composite lifting surface. Rayleigh-Ritz method is used to develop the equations of motion of a laminated plate-wing model with segmented piezoactuators. A state space aeroservoelastic mathematical model by rational function approximation (RFA) of the unsteady aerodynamic forces is derived. The minimum state method combined with the optimization technique is adapted for RFA. The linear quadratic regulator with output feedback is employed in active control of the system. The thickness and size of the piezoelectric actuators that affect the structural properties as well as the control characteristics are held constant. The optimal placement of piezoelectric actuators for flutter suppression subject to minimize the controller performance index is determined analytically by using the optimization technique. The results show the capability of piezoactuators for the control of wing flutter. Numerical simulations of a model with the optimal actuators placement show a substantial saving in control effort compared with the initial model.

Application of H∞ Control and Lqg with Frequency-Dependent Weight Syntheses to a Multivariable Active Flutter Suppression System

This paper describes the effectiveness of three robust control synthesis techniques applied to a multivariable active flutter suppression system using numerical simulations. These techniques are the mixed-sensitivity reduction in H∞ (H∞-mix), the normalized left coprime factorization robust stabilization in H∞ (H∞-normalized), and LQG with frequency-dependent weights (FWLQG), which are proposed in this paper. Although the plant is an unstable multi-input and multi-output system with large parameter variation, the FWLQG technique is superior to both H∞ synthesis techniques from the viewpoint of the increment of the flutter velocity, the time response and the solubility of control problems.