Flutter Suppression Research Articles

Prediction and active suppression of flutter in composite panel based on eigenvector orientation method

In this paper, the critical points of flutter of a composite panel predicted using a finite element model are studied using an eigenvector orientation method. Taking a supersonic simply supported panel and clamped panel models as examples, the accuracy of the eigenvector orientation method for predicting the critical points of flutter is verified, and the misjudgments of “channeling” (modal crossover) and other phenomena by traditional judgment methods are avoided. The piezoelectric actuators are combined with the upper and lower surfaces of the simply supported panel (clamped panel), and the aerodynamic parameters of each finite element are changed by activating the piezoelectric actuators. Based on linear quadratic adjustment theory, an optimal control method for the active flutter suppression is designed. The influence of the activation position of the different piezoelectric actuators on the critical points of flutter is studied to increase the flutter speed to an ideal range. The results show that the control torque generated by the piezoelectric actuators can offset the occurrence of flutter and provide a lead time for possible flutter control.

Optimal core design of MR based smart panels subject of flutter instability

This study deals with aeroelastic and flutter analyses of the partially treated MR sandwich plates in the supersonic airflow. It also identifies the optimal locations of the MR segments in the core layer, which results in maximum flutter boundaries of the MR sandwich plate, in response to the airflow. Classical and Mindlin plate theories, Hamilton’s principle and first order linear piston theory are employed to derive the governing equations of motion of the structure. The assumed mode technique is used to solve the equations and specify the instability bounds of the sandwich plate. An experiment on the dynamic characteristics of the partially treated sandwich plate incorporating MR fluid as the core layer is conducted to demonstrate validity of the developed model. Then, the effect of number and locations of the MR pockets on the flutter suppression of the sandwich plates is comprehensively investigated. Also, an optimization problem is formulated to identify the optimal locations of the MR treatments, which maximize flutter boundaries of the structure in different levels of the magnetic flux density.

Flutter suppression of wind turbine blade based on nonlinear block backstepping control

Aiming at solving the nonlinear flutter problem of aeroelastic system of wind turbine blades, a controller combing block backstepping control and variable pitch motion was designed. Based on the typical blade-section model of the spring-mass-damper and the second-order model of the pitch actuator, nonlinear aeroelastic equation of the system under steady aerodynamic was given. Considering the multivariable, strong coupling factors and the unitary pitch control of the wind turbine blade aeroelastic system, a state space equation for a single-input/multiple-output nonlinear model was deduced. Based on the principle of block control, a nonlinear system with block control standard was obtained, which was composed of two subsystems. In order to suppress blade flutter and protect the blade, backstepping control was used to control blade pitch motion. The nonlinear block backstepping controller was designed by constructing Lyapunov function, and time response which can track the dynamic error of system was demonstrated. The simulation results showed that the designed controller can converge the divergent chattering trend to zero, and make the system globally stable.

Real-Time Flow Control of Blade Section Using a Hydraulic Transmission System Based on an H-Inf Controller with LMI Design

Vibration and real-time flow control of the 2D blade section of wind turbines with three degrees of freedom (3-DOF), excited by external pitch motion, are investigated based on an H-inf (H∞) controller using linear-matrix-inequality (HIC/LMI) design. The real-time flow control for the purpose of aeroelastic flutter suppression includes not only the driving process of real-time physical equipment, but also the realization of real-time control algorithm in the physical controller. The aeroelastic system combined with pitch motion is controlled by a kind of HIC/LMI algorithm. The real-time external pitch motion is driven by rack-piston cylinder (RPC) using a hydraulic transmission system (HTS). The unsteady aerodynamic loads model is simplified by the HTS system. The HTS is actuated by a proportional-flow valve (PFV) which is controlled by another HIC/LMI algorithm, a novel algorithm for waveform tracking. According to the result of waveform tracking, the input current signal of PFV is realized by the configuration of the controller hardware system and its external circuits. In two types of HIC/LMI algorithms, controller stabilities are affirmed using Lyapunov analyses, and controller values are derived and obtained by using LMI designs. Flutter suppression for divergent and instable displacements is shown, with obvious controlled effects illustrated. An online monitoring experimental platform using hardware-in-the-loop simulation, based on Siemens S7-200 programmable logic controller (PLC) hardware and Kingview detection system, is built to implement pitch motion based on HTS and configure the signal input of PFV in pitch control.

Active Disturbance Rejection Control for Hypersonic Flutter Suppression Based on Parametric ROM

AbstractThis paper presents an active disturbance rejection control algorithm (ADRC) to suppress the hypersonic flutter of a three-degrees-of-freedom (3-DOF) two-dimensional (2D) airfoil operating ...

A Quick Assessment and Optimization Method for a Flutter Aerodynamic Measure of a Typical Flat Box Girder

Flutter is one of the most serious wind-induced vibration phenomena for long-span bridges and may cause the collapse of a bridge (e.g., the Old Tacoma Bridge, 1940). The selection and optimization of flutter aerodynamic measures are difficult in wind tunnel tests. It usually takes a long time and consumes more experimental materials. This paper presents a quick assessment and design optimization method for the flutter stability of a typical flat box girder of the long-span bridges. Numerical analysis could provide a reference for wind tunnel tests and improve the efficiency of the test process. Based on the modal energy exchange in the flutter microvibration process, the global energy input and local energy input are analyzed to investigate the vibration suppression mechanism of a flat steel box girder with an upper central stabilizer. Based on the comparison between the experimental and numerical data, a quick assessment method for the optimization work is proposed. It is practical to predict the effects of flutter suppression measures by numerical analysis. Thus, a wind tunnel test procedure for flutter aerodynamic measures is proposed which could save time and experimental materials.

Aeroelastic Stability and Nonlinear Flutter Analysis of Heated Panel with Temperature-Dependent Material Properties

AbstractWith the use of new structural materials and intelligent materials in aircraft panel manufacturing and flutter suppression, temperature-dependent material properties are increasingly outsta...

Passive Suppression of Panel Flutter Using a Nonlinear Energy Sink

A nonlinear energy sink (NES) is used to suppress panel flutter. A nonlinear aeroelastic model for a two-dimensional flat panel with an NES in supersonic flow is established using the Galerkin method. First-order piston aerodynamic theory is adopted to build the aerodynamic load. The effects of NES parameters on flutter boundaries of the panel are investigated using Lyapunov’s indirect method. The mechanism of the NES suppression of panel flutter is studied through energy analysis. Effects of NES parameters on aeroelastic responses of the panel are obtained, and a design technique is adopted to find a suitable combination of parameter values of the NES that suppresses the panel flutter effectively. Results show that the NES can increase or reduce the onset dynamic pressure of the panel flutter and it can reduce the aeroelastic response amplitude effectively within a certain range of dynamic pressure behind the onset dynamic pressure. The installation position of the NES depends on the direction of the airflow. The robust characteristics should be considered to find the suitable combination of parameter values of the NES.

Observer‐based synthesis of linear parameter‐varying mixed sensitivity controllers

SummaryThis article presents a computationally efficient way of synthesizing linear parameter‐varying (LPV) controllers. It reviews the possibility of a separate observer and state feedback synthesis with guaranteed performance and shows that a standard mixed sensitivity problem can be solved in this way. The resultant output feedback controller consists of an LPV observer, augmented with dynamic filters to incorporate integral control and roll‐off properties, and an LPV state feedback gain. It is thus highly structured, which is beneficial for implementation. Moreover, it does not depend on scheduling parameter rates regardless of whether parameter‐dependent Lyapunov matrices are used during synthesis. A representative control design for active flutter suppression on an aeroelastic unmanned aircraft demonstrates the benefits of the proposed method in comparison with state‐of‐the‐art LPV output feedback synthesis.

An overview of methods for investigation of aeroelastic response on high aspect ratio fixed-winged aircraft

The thrust of increasing environmental and economic constraints on aircraft has enthused accelerated research in design of more economical and higher performance aircraft. Extensive experience in aerodynamic has established the use of high aspect ratio wings to improve the lift-to-drag ratio, a key parameter in determination of aircraft efficiency. Application of long slender wings has even more so intensified in the last decade due to emerging need for medium-to-high altitude long endurance (MALE/HALE) unmanned aerial vehicles (UAVs). However, such a wing comes at a trade-off of efficiency and safety. Longer wings tend of be more flexible and easily deform under load, hence are more vulnerable to the detrimental nature of aeroelastic effects. Divergence, control reversal and flutter are some major aeroelastic effects, which range from mere discomfort to complete destruction of body in flight. UAVs are most susceptible to this behaviour as their design incorporates very high aspect ratio wings. Numerous researches are available in literature which have focused on the explanation, calculation, and suppression of aeroelasticity; a subject which is as old as first heavier-than-air flight. This paper has attempted to cover the major aspect of aeroelasticity and summarize the state-of-the-art methods and approaches proposed by esteemed authors in this field for flutter prediction and suppression.

LPV modeling and controller design for body freedom flutter suppression subject to actuator saturation

In recent years, the Active Flutter Suppression (AFS) employing Linear Parameter-Varying (LPV) framework has become a hot spot in the research field. Nevertheless, the flutter suppression technique is facing two severe challenges. On the one hand, due to the fatal risk of flight test near critical airspeed, it is hard to obtain the accurate mathematical model of the aeroelastic system from the testing data. On the other hand, saturation of the actuator may degrade the closed-loop performance, which was often neglected in the past work. To tackle these two problems, a new active controller design procedure is proposed to suppress flutter in this paper. Firstly, with the aid of LPV model order reduction method and State-space Model Interpolation of Local Estimates (SMILE) technique, a set of high-fidelity Linear Time-Invariant (LTI) models which are usually derived from flight tests at different subcritical airspeeds are reduced and interpolated to construct an LPV model of an aeroelastic system. And then, the unstable aeroelastic dynamics beyond critical airspeed are ‘predicted’ by extrapolating the resulting LPV model. Secondly, based on the control-oriented LPV model, an AFS controller in LPV framework which is composed of a nominal LPV controller and an LPV anti-windup compensator is designed to suppress the aeroelastic vibration and overcome the performance degradation caused by actuator saturation. Although the nominal LPV controller may have superior performance in linear simulation in which the saturation effect is ignored, the results of the numerical simulations show that the nominal LPV controller fails to suppress the Body Freedom Flutter (BFF) when encountering the actuator saturation. However, the LPV anti-windup compensator not only enhances the nominal controller’s performance but also helps the nominal controller to stabilize the unstable aeroelastic system when encountering serious actuator saturation.

Controllability Gramian as Control Design Objective in Aircraft Structural Design Optimization

Because of their higher aerodynamic efficiency and lighter structural weight, thin composite wings with large aspect ratios are increasingly being used for civil transport aircraft wing design. However, the increased flexibility can induce several performance issues, such as high deflections, reduced control authority, coupled flight dynamics, and, possibly, a reduction in the flutter speed. Therefore, including control surface and control law design at the conceptual design stage is becoming increasingly important. This paper presents a novel approach for integrating a control objective into an aircraft design optimization at the conceptual design stage by proposing the use of the eigenvalues of the controllability Gramian to enhance the controllability of an aircraft. The individual eigenvalues of the controllability Gramian quantify the energy required to move along the corresponding eigenvector, which is observed to be dominated by one state-space variable. A higher eigenvalue implies lower energy requirements for controlling that eigenvector, thus the corresponding state-space variable. This approach does not rely on a control law design but on modifying the open-loop system such that it is easier to control. The approach is applied to conduct multidisciplinary design analysis and optimization (MDAO) of a composite flying-wing test aircraft. A previously developed MDAO framework is used to design the internal structural layout, using curvilinear spars and ribs (SpaRibs) and straight spars and ribs. It is found that the optimal control designs have up to 8% higher flutter speed with a 3.7% weight penalty. Moreover, the frequencies of the vibration mode shapes are higher for the optimal control designs. The active flutter suppression controllers are designed after the MDAO process, and it is found that the optimal control designs have significantly higher gain and phase margins. As a result, the optimal control designs yield higher robust closed-loop flutter speed as compared with the weight-minimized design.

A neural network approach for improving airfoil active flutter suppression under control-input constraints

This study deals with improving airfoil active flutter suppression under control-input constraints from the optimal control perspective by proposing a novel optimal neural-network control. The proposed approach uses a modified value function approximation dynamically tuned by an extended Kalman filter to solve the Hamilton–Jacobi–Bellman equality online for continuously improved optimal control to address optimality in parameter-varying nonlinear systems. Control-input constraints are integrated into the controller synthesis by introducing a generalized nonquadratic cost function for control inputs. The feasibility of using a performance index involving the nonquadratic control-input cost with the modified value function approximation is examined through the Lyapunov stability analysis. Wind tunnel experiments were conducted for controller validation, where an optimal controller synthesized offline via linear parameter-varying technique was used as a benchmark and compared. It is shown, both theoretically and experimentally, that the proposed method can effectively improve airfoil active flutter suppression under control-input constraints.

Active Tilting Flutter Suppression of GyroWheel With Composite-Structured Adaptive Compensator

To improve the high-precision directivity of the GyroWheel (GW) during torque output, a composite-structured adaptive compensating method is proposed in this article, which achieves high frequency tilting flutter suppression of GW rotor. The composite structure includes adaptive seeking compensator and feedforward compensator. First, the tilting flutter of the fundamental frequency and twice frequency are equivalent to the periodic disturbance torques. The adaptive seeking algorithm is adopted to generate compensation signals of the same frequency and phase to reduce the flutter. Variable step size seeking method with threshold function can improve the convergence rate of the algorithm. Then, in the range of small tilting angle, an auxiliary feedforward compensator is designed according to GW disturbance torque model, which can improve the suppression rate of the twice frequency and avoid the influence of sensor noise. Finally, both numerical simulations and experiments have verified the effectiveness of the active tilting flutter suppression scheme, improving the stable torque output performance of GW as an actuator.

Superior aeroelastic behaviors of axially functional graded cylindrical shells in supersonic airflow

It is well known that mode localization occurs in the panel flutter structural systems. Therefore, it is reasonable to expect the aeroelastic stability of the structure to be enhanced by changing the geometrical sizes and material properties of the structure along the airflow direction. In this investigation, an axially functionally graded (AFG) cylindrical shell is designed and its super aeroelastic behaviors in supersonic airflow are studied. The enhanced aeroelastic stability and the excellent capability in the passive flutter suppression are achieved by the present AFG design. For the thickness of the cylindrical shell, three types of functions are analyzed. Numerical results show that all these three functions can increase the flutter bound of the cylindrical shell to some extent. It is also noted that in some situations, local mode coalescence happens. In this study, an effective method is proposed to eliminate the local mode coalescence by adding the lumped mass. For the material properties, two groups of functions are considered. It is found that under suitable parameters of the functions, even if the effective stiffness of the whole structural system decreases, the flutter bound of the structure can still be increased due to the AFG design. In addition, the flutter stability of the AFG cylindrical shell is much better than that of the traditional transversely functionally graded shell. The present study is significant in the aeroelastic design of aerospace vehicles.

Aeroelastic Wing Planform Design Optimization of a Flutter UAV Demonstrator

In this work, a study to design a highly flexible flutter demonstrator for the development and testing of active flutter suppression is presented. Based on the UAV mission, a bi-objective design optimization problem can be formulated. The aeroelastic UAV characteristic and imposed constraints, defined by operational aspects and the structural integrity are described by surrogate modeling. Within the framework of the multi-criteria optimization, an approach to construct the equally spaced Pareto frontier with a new approach for non-convex problems is presented. An efficient Pareto configuration to meet a natural low speed and low frequency is identified and its main influencing design features are analyzed.

Grid-Based and Polytopic Linear Parameter-Varying Modeling of Aeroelastic Aircraft with Parametric Control Surface Design

The main direction of aircraft design today and in the future is to achieve more lightweight and higher aspect ratio airframes with the aim to improve performance and to reduce operating costs and harmful emissions. This promotes the development of flexible aircraft structures with enhanced aeroelastic behaviour. Increased aeroservoelastic (ASE) effects such as flutter can be addressed by active control technologies. Control design for flutter suppression heavily depends on the control surface sizing. Control surface sizing is traditionally done in an iterative process, in which the sizing is determined considering solely engineering rules and the control laws are designed afterwards. However, in the case of flexible vehicles, flexible dynamics and rigid body control surface sizing may become coupled. This coupling can make the iterative process lengthy and challenging. As a solution, a parametric control surface design approach can be applied, which includes limitations of control laws in the design process. For this a set of parametric models is derived in the early stage of the aircraft design. Therefore, the control surfaces can be optimized in a single step with the control design. The purpose of this paper is to describe as well as assess the developed control surface parameterized ASE models of the mini Multi Utility Technology Testbed (MUTT) flexible aircraft, designed at the University of Minnesota. The ASE model is constructed by integrating aerodynamics, structural dynamics and rigid body dynamics. In order to be utilized for control design, control oriented, low order linear parameter-varying (LPV) models are developed using the bottom-up modeling approach. Both grid- and polytopic parametric LPV models are obtained and assessed.

The effect of magnetorheological fluid and aerodynamic damping on the flutter boundaries of MR fluid sandwich plates in supersonic airflow

The present study deals with aeroelastic stability analysis of sandwich plates, containing magnetorheological fluid as the core layer, subjected to the supersonic airflow. The classical plate theory, Hamilton's principle and linear first-order piston theory have been employed to extract the governing equations of motion of the structure. The assumed mode method is used to solve the derived equations and identify the instability region of the sandwich plate. In order to demonstrate validity of the proposed solution, an experiment on a cantilever sandwich plate consisting of polyethylene terephthalate (PET) as the face layers and MR fluid (MRF 132DG) as the core layer is conducted. In this study, the primary attention is focused on the effect of MR fluid and aerodynamic damping on the stability of the MR sandwich plates. Furthermore, the effect of magnetic flux, boundary conditions and plate parameters on the flutter boundaries of the sandwich MR plates are investigated. The results highlight the significance of MR fluid and aerodynamic damping in the flutter suppression of the sandwich plate structures, in a wide range of aerodynamic pressure.

Effects research on theoretical-modelling based suppression of the contact flutter in blisk belt grinding

Blisk is one of the critical parts of aero-engine whose surface processing quality directly affects the performance of aero-engine. The vibration phenomenon usually happened in the novel open belt grinding, and seriously affects the dimension precision as well as the surface quality of the whole blade profile. In order to figure out that, this paper established a vibration model for the blisk belt grinding. The weak rigidity characteristics of the system were analyzed initially, and the vibratory mechanism was revealed from the view of dynamic analysis. Based on the theoretical model, the stability conditions were proposed by analyzing the influencing of vital factors on processing stability. The experimental validation indicated that the vibration signal waveforms during the process had been successfully reduced by introducing adjustment of grinding parameters. The profile accuracy of the blade contour edge was improved by 9.53 % from the range of −0.0376–0.1145 mm to that of −0.0359–0.1017 mm. After parameter adjustment, the smoothness of the micro-morphology of the blade surface was improved, and the roughness of the blade surface decreased from Ra 0.379–0.573 μm to 0.291–0.368 μm, which fully met the processing requirement of Ra <0.4 μm.

Research on Vibration Suppression for AGARD Wing Based on State Space Model

Based on the Observer method, the unsteady aerodynamic reduced order model is established. The aerodynamic, structural and control parts are in the form of state space equations. The state feedback control law is designed by linear quadratic regulator (LQR) method, and the active flutter suppression of aeroelastic system is realized. The three-dimensional AGARD elastic wing is selected as an example. The simulation results show that the active control law designed by the model reduction technique can effectively stabilize the response of the system, and the critical speed of closed-loop flutter increases greatly.