Active Flutter Control Research Articles

A smart rotor configuration with linear quadratic control of adaptive trailing edge flaps for active load alleviation

AbstractThe paper proposes a smart rotor configuration where adaptive trailing edge flaps (ATEFs) are employed for active alleviation of the aerodynamic loads on the blades of the NREL 5 MW reference turbine. The flaps extend for 20% of the blade length and are controlled by a linear quadratic (LQ) algorithm based on measurements of the blade root flapwise bending moment. The control algorithm includes frequency weighting to discourage flap activity at frequencies higher than 0.5 Hz. The linear model required by the LQ algorithm is obtained from subspace system identification; periodic disturbance signals described by simple functions of the blade azimuthal position are included in the identification to avoid biases from the periodic load variations observed on a rotating blade. The LQ controller uses the same periodic disturbance signals to handle anticipation of the loads periodic component. The effects of active flap control are assessed with aeroelastic simulations of the turbine in normal operation conditions, as prescribed by the International Electrotechnical Commission standard. The turbine lifetime fatigue damage equivalent loads provide a convenient summary of the results achieved with ATEF control: 10% reduction of the blade root flapwise bending moment is reported in the simplest control configuration, whereas reductions of approximately 14% are achieved by including periodic loads anticipation. The simulations also highlight impacts on the fatigue damage loads in other parts of the structure, in particular, an increase of the blade torsion moment and a reduction of the tower fore‐aft loads. Copyright © 2014 John Wiley & Sons, Ltd.

Aeroelastic analysis and active flutter control of nonlinear lattice sandwich beams

Nonlinear aeroelastic characteristics of sandwich beams with pyramidal lattice core are investigated, and the active flutter control of the nonlinear structural system is also studied using the piezoelectric actuator/sensor pair. In the structural modeling, Reddy’s third-order shear deformation theory is applied. Aerodynamic pressure is evaluated by the supersonic piston theory. Hamilton’s principle and the assumed mode method are used to derive the equation of motion. The proportional feedback and the optimal H∞ control methods are performed to design the controller. In the robust control, the uncertainty caused by omitting the nonlinear terms of the control equation is taken into account, and the mixed sensitivity method is used to solve the problem. The nonlinear aeroelastic property of the sandwich beam is analyzed and is compared with that of the equivalent isotropic beam with the same weight to show the superior aeroelastic characteristics of the lattice sandwich beam. Controlled vibration responses under the two different controllers are calculated and compared. Simulation results show that the robust controller is much more effective than the proportional feedback controller in the flutter suppression of the nonlinear sandwich beam.

Aerothermoelastic analysis and active flutter control of supersonic composite laminated cylindrical shells

The aerothermoelastic characteristics of the supersonic laminated cylindrical shell are analyzed, and the active flutter control of the aeroelastic structure is also investigated using the piezoelectric material. In the structural modeling, the influences of the in-plane thermal load on the transverse deformation are taken into account. The aerodynamic pressure is evaluated using the supersonic piston theory. Hamilton’s principle and the Galerkin’s method are used to establish the equation of motion. The proportional feedback and LQG control methods are applied to design the controller. The aerothermoelastic analysis for the laminated cylindrical shell is carried out using the frequency- and time-domain methods. The influences of the ply angle on the flutter and thermal buckling properties are investigated. The active flutter control effects of different controllers are compared. Numerical simulation shows that the LQG controller is more accurate and effective than the LQR and proportional feedback controllers.

Active control of hypersonic airfoil flutter via adaptive fuzzy sliding mode method

This paper presents a novel adaptive active control method, which is used for the flutter suppression problem in hypersonic flow. First, the system’s stability is analyzed and the Hopf bifurcation points are obtained. Then, fuzzy systems are employed to approximate the system’s nonlinear dynamics. Furthermore, in order to increase the robustness of the system, a sliding surface is designed by introducing an integral operator. Thirdly, by Lyapunov theory, the proposed fuzzy sliding mode active control guarantees the convergence of flutter and the global boundedness of all the signals in the closed-loop system. The simulation results demonstrate the effectiveness of the proposed method.

Optimal locations of piezoelectric actuators and sensors for supersonic flutter control of composite laminated panels

The optimal active flutter control of supersonic composite laminated panels is studied using the distributed piezoelectric actuators/sensors pairs. The supersonic piston theory is used to calculate the unsteady aerodynamic pressure, and Hamilton’s principle with the assumed mode method is employed to develop the equation of motion of the structural system. The controllers are designed by the proportional feedback control method and the linear quadratic Gauss (LQG) algorithm. The optimal locations of the actuator/sensor pairs are determined by the genetic algorithm (GA). The aeroelastic properties of the structural system are mainly analyzed using the frequency-domain method. The time-domain responses of the structure are also computed using the Runge–Kutta method. The influences of ply angle on the flutter bound of the laminated panel with different length–width ratios are analyzed. The optimal design for the locations for different numbers of piezoelectric patches used in the proportional feedback control is carried out through the GA. Meanwhile, the control effects using different numbers of actuator/sensor pairs are investigated. The flutter suppression by the LQG algorithm is also carried out. The control effects using the two different controllers are compared. Numerical simulations show that the optimal locations obtained by the GA can increase the critical flutter aerodynamic pressure significantly, and the LQG algorithm is more effective in flutter suppression for supersonic structures than the proportional feedback controller.

Study on Cable-Stayed Bridge Flutter Active Control by a Single ADM

Wind-induced vibration of long span bridges mainly as flutter, buffeting and vortex induced vibration. Buffeting and vortex-induced vibration will not cause the devastating destruction of the bridge, while the chatter is the elastic system in the air of self-excited vibration, when the vibration system from the air flow in the absorption of energy and the energy is greater than the energy damping When consumed, they cause divergence of the self-excited aerodynamic flutter vibration. If the critical flutter wind speed is less than in the bridge office potential wind speed, the bridge flutter may occur caused devastating damage. According to modern control theory, a theoretical analysis is conducted on the active control of cable-stayed bridge flutter, it is established that the controlled equation of cable-stayed bridge controlled by a single active mass damper and the motion equation of a single AMD to determine the calculation method of the critical flutter velocity under the controlled status of the cable-stayed bridge. An example shows that a single ADM is a good means to prevent the flutter damage of long-span cable-stayed bridges.

Active control of supersonic/hypersonic aeroelastic flutter for a two-dimensional airfoil with flap

The flutter, post-flutter and active control of a two-dimensional airfoil with control surface operating in supersonic/hypersonic flight speed regions are investigated in this paper. A three-degree-of-freedom dynamic model is established, in which both the cubic nonlinear structural stiffness and the nonlinear aerodynamic load are accounted for. The third order Piston Theory is employed to derive the aerodynamic loads in the supersonic/hypersonic airflow. Nonlinear flutter happens with a phenomenon of limit cycle oscillations (LCOs) when the flight speed is less than or greater than linear critical speed. The LQR approach is employed to design a control law to increase both the linear and nonlinear critical speeds of aerodynamic flutter, and then a combined control law is proposed in order to reduce the amplitude of LCOs by adding a cubic nonlinear feedback control. The dynamic responses of the controlled system are given and used to compare with those of the uncontrolled system. Results of simulation show that the active flutter control method proposed here is effective.

Active aeroelastic flutter analysis and vibration control of supersonic beams using thepiezoelectric actuator/sensor pairs

The active vibration control of all kinds of structures by using the piezoelectric materialhas been extensively investigated. In this paper, the active aeroelastic flutter characteristicsand vibration control of supersonic beams applying the piezoelectric material are studiedfurther. The piezoelectric materials are bonded on the top and bottom surfaces of thebeams to act as the actuator and sensor so that the active aeroelastic flutter suppressionfor the supersonic beams can be conducted. The supersonic piston theory is adopted toevaluate the aerodynamic pressure. Hamilton’s principle with the assumed modemethod is used to develop the dynamical model of the structural systems. By usingthe standard eigenvalue methodology, the solutions for the complex eigenvalueproblem are obtained. A negative velocity feedback control strategy is used toobtain active damping. The aeroelastic flutter bounds are calculated and the activeaeroelastic flutter characteristics are analyzed. The impulse responses of the structuralsystem are obtained by using the Houbolt numerical algorithm to study the activeaeroelastic vibration control. The influences of the non-dimensional aerodynamicpressure on the active flutter control are analyzed. From the numerical results it isobserved that the aeroelastic flutter characteristics of the supersonic beams canbe significantly improved and that the aeroelastic vibration amplitudes can beremarkably reduced, especially at the flutter points, by using the piezoelectricactuator/sensor pairs which can provide an active damping. Within a certain value of thefeedback control gain, with the increase of it, the flutter aerodynamic pressure(or flutter velocity) can be increased and the control results are also improved.

Active Feedback Control of a Web Flutter Using Flow Control Devices

This paper develops a non-contact active feedback control of web flutter in a narrow passage by using movable plates set at inlet and outlet of the passage. The strategy of this active feedback control is based on the flow-control which cancels the exciting fluid force acting on the web, i.e., cancels the self-excited feedback mechanism. In this paper, suppression of the web flutter by the active feedback control is demonstrated experimentally. In the experiments, a web (film), as a controlled object, is subjected to air flow in a narrow passage. The web flutter occurs to the web in the translational motion over the critical flow velocity. And the web flutter is actively controlled and suppressed by the movable plate motion which changes the air flow in the passage. The critical flow velocity under controlled condition is examined with changing the controller gain and phase-shift between the web motion and the movable plate motion. As a result, it is indicated that the active feedback control increases the critical flow velocity, and suppress the web flutter effectively. Moreover, the control performance is examined experimentally, and stabilization mechanism by the active feedback control is discussed.

2D22 Active Control of a Web Flutter by a Non-contact Control Device Using Pressure Wave

2D22 Active Control of a Web Flutter by a Non-contact Control Device Using Pressure Wave

Stability investigation of an airfoil section with active flap control

AbstractThis work presents a method to determine flutter and divergence instability limits for a two‐dimensional (2‐D) airfoil section fitted with an actively controlled trailing edge flap. This flap consists of a deformable trailing edge, which deformation is governed by control algorithms based on measurements of either heave displacement, local angle of attack or aerodynamic pressure difference measured over the airfoil. The purpose of the controlled deformable flap is to reduce fluctuations in the aerodynamic forces on the airfoil, which, according to recent studies, have a significant potential for fatigue load alleviation. The structural model of the 2‐D airfoil section contains three degrees of freedom: heave translation, pitch rotation and flap deflection. A potential flow model provides the aerodynamic forces and their distribution. The unsteady aerodynamics are described using an indicial function approximation. Stability of the full aeroservoelastic system is determined through eigenvalue analysis by state–space formulation of the indicial approximation. Validation is carried out against an implementation of the recursive method by Theodorsen and Garrick for ‘flexure–torsion–aileron’ flutter. The implemented stability tool is then applied to an airfoil section representative of a wind turbine blade with active flap control. It is thereby observed that the airfoil stability limits are significantly modified by the presence of the flap, and they depend on several parameters: flap structural characteristics, type of control, control gain factors and time lag. Copyright © 2009 John Wiley & Sons, Ltd.

AEROELASTIC ANALYSIS OF BEARINGLESS ROTOR SYSTEMS WITH TRAILING EDGE FLAPS

An aeroelastic analysis of bearingless rotor systems with trailing edge flaps was conducted using large deflection-type beam theory for forward flight conditions with a focus on reducing vibration while minimizing control effort. The aerodynamic forces of the rotor blade were calculated using two-dimensional quasi-steady strip theory. For the analysis of forward flight, the nonlinear periodic blade steady response was obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The objective function, which includes vibratory hub loads and active flap control inputs, was minimized by an optimal control process. Numerical simulations were performed for the steady-state forward flight of various advance ratios. Numerical results of the steady blade and flap deflections as well as the vibratory hub loads were also presented for various advance ratios and were compared with previously published analysis results obtained from modal analyses based on a moderate deflection-type beam theory.

Aeroelastic analysis of rotor systems using trailing edge flaps

An aeroelastic analysis of rotor blades with trailing edge flaps was conducted using large deflection-type beam theory for forward flight conditions with a focus on reducing vibration while minimizing control effort. The aerodynamic forces of the rotor blade were calculated using two-dimensional quasi-steady strip theory. For the analysis of forward flight, the nonlinear periodic blade steady response was obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The objective function, which includes vibratory hub loads and active flap control inputs, was minimized by an optimal control process. Numerical simulations were performed for the steady-state forward flight of various advance ratios. Numerical results of the steady blade and flap deflections as well as the vibratory hub loads were also presented for various advance ratios and were compared with previously published analysis results obtained from modal analyses based on a moderate deflection-type beam theory.

Suppression of Thermal Postbuckling and Nonlinear Panel Flutter Motions Using Piezoelectric Actuators

Active output feedback control of large amplitude nonlinear panel flutter at supersonic speeds with and without temperature effect is presented. A coupled structural-electrical modal formulation using finite elements is applied. Suppression of three types of panel response is studied: limit cycle oscillations, static thermal postbuckling, and chaotic motion. The controller, composed of a linear quadratic regulator and an extended Kalman filter, is developed and investigated. The extended Kalman filter considers the nonlinear state-space matrix and has a gain sequence evaluated online. The norms of the feedback control gain are employed for the optimal placement of piezoelectric actuators, and the norms of the Kalman filter estimation gain are used to validate the best locations for the sensors. A symmetric laminated composite plate at supersonic speeds with or without the influence of elevated temperatures is investigated. Two types of piezoelectric materials, PZT5A and macrofiber composite actuators, embedded in the composite panel are considered to suppress the nonlinear panel flutter. Simulation results show that the linear quadratic regulator/Kalman filter controller can suppress all three types of panel response with or without thermal effects.

Aeroelastic Characteri stics of Rotor Blades with Trailing Edge Flaps

The aeroelastic analysis of rotor blades with trailing edge flaps, focused on reducing vibration while minimizing control effort, are investigated using large deflection-type beam theory in forward flight. The rotor blade aerodynamic forces are calculated using two-dimensional quasi-steady strip theory. For the analysis of forward flight, the nonlinear periodic blade steady response is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The objective function, which includes vibratory hub loads and active flap control inputs, is minimized by an optimal control process. Numerical simulations are performed for the steady-state forward flight of various advance ratios. Also, numerical results of the steady blade and flap deflections, and the vibratory hub loads are presented for various advance ratios and are compared with the previously published analysis results obtained from modal analysis based on a moderate deflection-type beam theory.

Active Control of Wing Flutter Using Piezoactuated Surface

Flutter suppression concept is demonstrated by performin wind-tunnel tests in a low subsonic flow regime. The wing model, witha trailing edge control surface, is constructed to have a bending-torsion flutter. The control surface is actuated by a flexure-hinged lead zirconate titanate stack mechanism acting as an aerodynamic effector. The flutter experiments are conducted using a digital controller, implemented in dSPACE DS1104, keeping the wing model at 4 deg angle of attack. The wing response is measured by lead zirconate titanate sensors, which are used to generate the feedback control to vibrate the control surface in antiphase motion with respect to the main surface to introduce active aerodynamic control. It is noticed that both bending and torsion modes are stabilized in dosed-loop configurations. The damping trend of the flutter mode shows an expanded flutter envelope that is estimated to be around 20%. The actuators are operated within 1000 V/mm, though their allowable field13; strength is 1500 V/ mm.

Active Control of Nonlinear Panel Flutter Under Yawed Supersonic Flow

A coupled structural-electrical modal finite element formulation for composite panels with embedded piezoelectric sensors and actuators is presented for nonlinear panel flutter suppression under yawed supersonic flow. The first-order shear deformation theory for laminated composite plates, the von Karman nonlinear strain-displacement relations for large deflection response, the linear piezoelectricity constitutive relations, and the first-order piston theory of aerodynamics are employed. Nonlinear equations of motion are derived by extending the three-node triangular Mindlin (MIN3) plate element. Additional electrical degrees of freedom are introduced to model piezoelectric sensors and actuators. The system equations of motion are transformed and reduced to a set of nonlinear equations in modal coordinates. Analysis results for the effect of arbitrary flow yaw angle on nonlinear supersonic panel flutter are presented. The results show that the flow yaw angle has a major effect on the panel limit-cycle oscillation amplitude and deflection shape. Two different control methods are investigated for the suppression of nonlinear panel flutter. The first method is the linear quadratic Gaussian controller. The second method is the nonlinear output controller comprised of a linear quadratic regulator and an extended Kalman filter nonlinear state estimator. Closed-loop criteria based on the norm of feedback control gain and on the norm of Kalman filter estimator gain are used to determine the optimal location of piezoelectric actuators and sensors at different flow yaw angles. Optimal sensor and actuator locations for a range of yaw angles are determined by grouping the optimal locations for different angles within the range. The results demonstrate the effectiveness of piezoelectric materials and of the nonlinear output controller in suppressing nonlinear flutter of isotropic and composite panels at different flow yaw angles.

Active aeroelastic control of 2-D wing-flap systems operating in an incompressible flowfield and impacted by a blast pulse

This paper concerns the active aeroelastic control of 2-D wing-flap systems operating in an incompressible flowfield and exposed to a blast pulse. The goal is to implement an active flap control capability to suppress the flutter instability and enhance the subcritical aeroelastic response to time-dependent external pulses. To this end, a combined control law is implemented and its performances toward suppressing flutter and reducing the vibrational level in the subcritical flight speed range is demonstrated.

Simulation of transonic flutter and active shockwave control

Transonic flutter and active flap control, in two dimensions, are simulated by coupling independent structural dynamic and inviscid aerodynamic models, in the time domain. A flight control system, to actively control the trailing edge flap motion, has also been incorporated and, since this requires perfect synchronisation of fluid, structure and control signal, the “strong” coupling approach is adopted. The computational method developed is used to perform transonic aeroelastic and aeroservoelastic calculations in the time domain, and used to compute stability (flutter) boundaries of 2D wing sections. Open and closed loop simulations show that active control can successfully suppress flutter and results in a significant increase in the allowable speed index in the transonic regime. It is also shown that active control is still effective when there is free‐play in the control surface hinge. Flowfield analysis is used to investigate the nature of flutter and active control, and the fundamental importance of shock wave motion in the vicinity of the flap is demonstrated.

Numerical-experimental simulation of active flutter control for bridges

A coupled numerical and experimental simulation is used to investigate active flutter control for wind-induced vibrations of a bridge girder. In addition to performance, the stability of a controlled aeroelastic structure is of great concern. The analytical model of the aeroelastic plant including flutter derivatives, is parametrized by frequency of motion and wind velocity. The flutter derivatives are obtained by the forced vibration method. The critical wind speeds of the uncontrolled and the controlled structure are determined analytically using the Hurwitz criterion and experimentally using the numerical–experimental set-up, which includes a scaled model in a water channel. The analytical and experimental results show good agreement. Control scenarios under smooth and turbulent flow conditions have been simulated. Furthermore, the effect of saturation in active control on performance and on flutter stability has been studied. The example of a long-span suspension bridge is used to demonstrate the effectiveness of the proposed coupled numerical and experimental scheme for flutter control simulation. Copyright © 2004 John Wiley & Sons, Ltd.