Aeroelastic Control Research Articles

Nonlinear flap for passive flutter control of bidimensional wing

A solution for passive aeroelastic control is presented and tested experimentally on a bidimensional wing setup. The solution consists of a flap integrated in the wing which acts as a secondary mass damper and absorbs energy when aeroelastic instability is encountered. This device is passive, which makes it safe in emergency cases and adds little mass to the system in the fundamental case presented in this paper. If installed on actual aircraft wings, the flap-NES would not substitute but coexist with classic active control methods, adding virtually zero mass to the existing system. Using a flap placed in the airflow enables the control system to benefit from aerodynamic damping with a behavior dependent on wind speed. The device can either have a linear or nonlinear stiffness. It is shown that both options absorb energy from the main system, that is, the wing. The flap acts as a TMD (tuned mass damper) in the linear case and as an NES (nonlinear energy sink) in the nonlinear case. The nonlinear solution not only absorbs more energy at given wind speed but it also is a more suited solution as the damper follows the wind speed dependent frequencies due to its nonlinear feature. In this work, the flap-TMD and the flap-NES are tested experimentally on a bidimensional wing which presents classic flutter.

Development of an Active Wingtip for Aeroelastic Control

This paper presents the design of an innovative wingtip device actively actuated to control the aeroelastic loads, with a focus on the gust load alleviation. It summarizes the work carried out in the Clean Sky 2 AIRGREEN2 project, where the device was developed from scratch and reached a relevant technology readiness level with the full-scale prototype manufacturing and testing, compulsory to obtain the permit to fly. This paper describes the overall design of the devices, covering the structure, the aero-servo-elasticity characteristics of the whole aircraft, the actuation system design, the scaled wind tunnel testing, and the full-scale structural qualification tests. The paper proves how the development of a new item involves several disciplines simultaneously, remarking on the importance of an integrated approach to the new generation aircraft design.

Analytical modeling of panel flutter and active control in supersonic variable stiffness composite laminates

This work focuses on panel flutter and active control in supersonic variable stiffness composite laminates, making progress on the analytical modeling and combined exploration of curvilinear fiber composites tailoring and piezoelectric sensors/actuators, as promising structural design technologies, for aeroelastic control. The Classical Laminated Plate Theory and the First-Order Piston Theory are used as structural and aerodynamic models, respectively. Flutter analyses are carried out for simply supported plates, either purely elastic laminates or piezoelectric composite laminates. The tailor-ability of curvilinear fiber composites and the effect of proportional control are discussed. Ultimately, the presented results provide a comprehensive benchmark for future assessments.

Aeroelastic control of delaminated variable angle tow laminated composite plate using piezoelectric patches

The free vibration and aeroelastic analysis of variable angle tow (VAT) laminated composite plate bonded with discrete piezoelectric patches are considered for investigation. A finite element (FE) model is developed using eight noded isoparametric elements to study the impact of delamination size and location on the dynamic response of smart VAT laminated plates. For aeroelastic analysis, the FE model is coupled with MSC. Nastran through Direct Matrix Abstraction Program (DMAP) and the structural parameters obtained with the FE model are supplied to MSC. Nastran solver to generate aerodynamic force matrix using Doublet Lattice Method (DLM). Various parametric studies are performed to find the most critical location of the delamination that severely affects vibration and flutter characteristics. The results showed that the delamination near the leading edge which faces free stream wind is found to be the most critical for the dynamic aeroelastic failure of structures. Further, the most effective location of the piezoelectric patches is identified to enhance the aeroelastic boundary of smart delaminated VAT composite plates using active displacement and velocity feedback gains.

A nonlinear aerothermoelastic model for slender composite beam-like wings with embedded shape memory alloys

This paper reports the formulation of an aerothermoelastic tool developed to investigate the behavior of flexible beam-like wings made of a hybrid adaptive material. Here, hybrid materials are defined as laminated composites additionally reinforced with embedded shape memory alloy wires. As main novelties, the proposed model couples geometrical, material, and aerodynamic nonlinearities to the thermal dynamics of SMA wires undergoing Joule’s effects, thereby establishing a multi-physical nonlinear problem. Geometrical nonlinearities were taken into account via an FE model of a 2D Timoshenko’s beam experiencing large deformations. Material nonlinearities were incorporated by a semi-empirical micro-mechanical model that computes the properties of hybrid laminates. To complement, nonlinear aerodynamic effects were introduced via an unsteady strip theory method in the time-domain, along with a nonlinear stall model and an assumption of follower aerodynamic forces. A set of numerical aerothermoelastic cases was performed by assuming various layups and SMA temperatures, with the objective of tailoring the aeroelastic response of hybrid wings. These cases were shown to lead to a considerable reduction in both post-flutter oscillations and post-divergence amplitudes as the SMA temperature increases. The outcomes have indicated compelling evidences on the applicability of embedded SMAs for structural, shape or aeroelastic control of flexible wings.

Hybrid control technique applied to an aero-servo-viscoelastic simplified wing model

Considering that flutter represents a potential catastrophic event in the context of aerospace structures, numerous studies have evaluated a number of strategies to avoid and/or control this kind of aeroelastic phenomenon. Currently, both active and passive control have been investigated to prevent instabilities induced by the interaction between aerodynamic and structural forces. It is also important to highlight the successful cases in which passive control techniques using viscoelastic materials have been useful to mitigate several types of vibration problems. However, there are still opportunities to explore the potential of control using viscoelastic material in the scope of aeroelasticity, especially when involving its combination with other control techniques. Therefore, this work presents a strategy involving a hybrid approach to aeroelastic control of a simplified unswept and untapered wing, using a combination of passive and active techniques. Passive control is achieved by the use of viscoelastic materials inserted as resilient elements in the aeroelastic model, while active control is performed by means of the deflections of a flap-like aerodynamic control surface, governed by a proportional-derivative control law. The results show that the application of the passive control alone causes an increase of up to 25.4% in critical flutter speed. In addition, the association of passive and active controls lead to higher control performance and the critical speed is increased by a further 6.8%, thus providing a broader safe flight speed range. Hence, the investigation indicates that the hybrid control approach exploring viscoelastic materials can be advantageous in practical applications.

Optimum aeroelastic control via iterative neural network training for wind-resistant cyber–physical buildings

This research presents iterative optimum training (IOT), which integrates deep neural networks (DNNs) and population-based optimization techniques such as genetic algorithms (GAs). The proposed technique reduces the number of experiments needed for training without adding complexity compared with non-iterative DNN-GA techniques commonly used in the literature. In this work, IOT is used to train an optimal controller for minimizing wind-induced vibration (WIV) using distributed aerodynamic actuators. Wind tunnel experiments of a scaled cyber–physical aeroelastic building model are used to demonstrate a novel application of the technique. IOT trains a DNN to approximate building vibration at different wind conditions and actuator orientations using an initial set of experiments. After this initial training, a GA uses the DNN to predict actuator orientations that minimize WIV for the given wind condition. A group containing best orientations from the GA and uniform random orientations is used to perform additional experiments and training of the DNN to enhance exploitation and exploration. This process is repeated until the stopping criteria is achieved. This paper includes results of a benchmark study comparing IOT to GA and DNN-GA techniques. Experimental results show that IOT-based online control of the aeroelastic model reduces WIV acceleration amplitudes by up to 90% within 9.8 s upon controller activation.

Interpolation-Based Modeling Methodology for Efficient Aeroelastic Control of a Folding Wing

The aeroelastic model of a folding wing varies with different configurations, so it actually represents a parameter-varying system. Firstly, a new approach based on interpolation of local models is proposed to generate the linear parameter-varying model of a folding wing. This model is capable of predicting the aeroelastic responses during the slow morphing process and is suitable for subsequent control synthesis. The underlying inconsistencies among local linear time-invariant (LTI) models are solved through the modal matching of structural modes and the special treatment of the rational functions in aerodynamic models. Once the local LTI models are represented in a coherent state-space form, the aeroservoelastic (ASE) model at any operating point can be immediately generated by the matrix interpolation technique. Next, based on the present ASE model, the design of a parameterized controller for suppressing the gust-induced vibration is studied. The receptance method is applied to derive fixed point controllers, and the effective independence method is adopted and modified for optimal sensor placement in variable configurations, which can avoid solving ill-conditioned feedback gains. Numerical simulation demonstrates the effectiveness of the proposed interpolation-based modeling approach, and the parameterized controller exhibits a good gust mitigation effect within a wide parameter-varying range. This paper provides an effective and practical solution for modeling and control of the parameterized aeroelastic system.

Flutter instability and active aeroelastic control with time delay for a two-dimensional airfoil

This paper studies the stability of a two-dimensional controlled airfoil system with time delay. First of all, a hybrid approach based on the frequency sweep test and the eigenvalue problem approximation using the Taylor series expansion of the delayed term is proposed to predict the critical time delay as well as the angular frequency of flutter instability. The efficiency of the proposed approach is illustrated by numerical examples for the prediction of self-sustaining vibrations of a phenomenological airfoil model with two degrees of freedom. One point of interest is to bring an understanding of the physical phenomena of the dynamic behavior involved in the appearance of flutter for the controlled airfoil system with time delay. Numerical results indicate that although one active controller is effective in suppressing airfoil flutter in a controlled system without time delay, control failure may happen depending on the time delay in control design. Secondly not only the effectiveness but also some drawbacks of two proposed controllers, namely the linear quadratic regulator state-feedback controller and the pole placement approach, are discussed through numerical simulations.

Structural damping models for passive aeroelastic control

Aeroelastic qualification requirements are typically met by sizing aircraft to achieve adequate stability margins and keep peak gust responses below specified thresholds. A possible alternative approach is delaying flutter and alleviating gust response by embedding dissipative materials into structural components. This approach requires accurate damping models applicable to the analysis of complex configurations. In this paper, the effect of damping models in the evaluation of flutter boundaries and gust response of an aeroelastic test-bed is studied. In particular, three damping models completely different in frequency are considered to model the presence of skin patches for passive aeroelastic control: viscous damping, hysteretic damping and Biot damping models. In order to make them comparable the three models are tuned in order to dissipate the same amount of power at the flutter frequency by means of the introduction and definition of a generalized loss factor. The damping models are compared by evaluating their effect on flutter suppression and gust load alleviation. Finally, the sensitiveness of the stability and response aeroelastic analyses to the considered damping models are outlined and the obtained results are compared to provide modeling recommendations for passive flutter suppression and gust alleviation studies. The proposed methodology is applicable to any linear material model for which the related complex stiffness can be expressed in the frequency domain meeting the Hilbert restriction.

Raptor wing morphing with flight speed.

In gliding flight, birds morph their wings and tails to control their flight trajectory and speed. Using high-resolution videogrammetry, we reconstructed accurate and detailed three-dimensional geometries of gliding flights for three raptors (barn owl, Tyto alba; tawny owl, Strix aluco, and goshawk, Accipiter gentilis). Wing shapes were highly repeatable and shoulder actuation was a key component of reconfiguring the overall planform and controlling angle of attack. The three birds shared common spanwise patterns of wing twist, an inverse relationship between twist and peak camber, and held their wings depressed below their shoulder in an anhedral configuration. With increased speed, all three birds tended to reduce camber throughout the wing, and their wings bent in a saddle-shape pattern. A number of morphing features suggest that the coordinated movements of the wing and tail support efficient flight, and that the tail may act to modulate wing camber through indirect aeroelastic control.

Dynamic Analysis of Flexible Wind Turbine Tower by a Transfer Matrix Method

To generate more power, wind turbine rotors are growing in size and consequently, wind turbine tower are becoming increasingly taller and more flexible. As a result, fluid–structure interaction (FSI) of the flexible tower caused by strong wind is a very important phenomenon, and tower vibration must be carefully considered. In this paper, the physical model of the wind turbine tower is simplified appropriately, and then a multi-body dynamics model of wind turbine tower system is established based on Transfer Matrix Method of Multibody System (MSTMM). Compared with the data from finite element model (FEM) and field tests, the simulation results show that the model has a good accuracy. By coupling the mode shapes with two degrees of freedom (2-DOF) wake oscillator model, the dynamic responses of the flexible tower are computed. The influence of various foundation stiffness and top mass on tower vibration is studied systematically using this model. The results indicate that different boundary conditions can affect the maximum amplitude and displacement along the axis of the tower. This work provides a reference for dynamic modeling and simulation of high-rise flexible structure, and the prediction of the maximum amplitude of the tower vibration, which can be used for aeroelastic control purpose.

Comparison of different plasma actuation strategies for aeroelastic control on a linear compressor cascade

The objective of this paper is to investigate the effects of Dielectric Barrier Discharge (DBD) plasma actuators on the aeroelastic control of a subsonic compressor cascade, for unsteady load mitigation and enhancement in the cascade aeroelastic response. Numerical simulations of the blades oscillating in traveling wave mode are performed with the commercial solver Ansys FLUENT®. Results are then validated through comparison with experimental data to assess the stability and convergence of the reference grid. Aeroelastic control is achieved by means of two AC-DBD plasma actuators installed on the trailing edge of the compressor blades, one on the suction side and one on the pressure side. Alleviation of the blade load is realized by operating alternately the actuators through a cosinusoidal function. Moreover, the effect of the actuation force phase on the blade load control is evaluated. Based on the actuation phase, results show that it is possible to manipulate effectively the unsteady lift and moment coefficients, stabilizing the compressor performance, alleviating fatigue phenomena and enlarging the flutter limits of the cascade. Plasma actuators confirm to be a very promising technology for active flow control in turbomachines and aeronautical applications.

Aeroelastic Control and Estimation with a Minimal Nonlinear Modal Description

Modal-based nonlinear moving horizon estimation (MHE) and model predictive control (MPC) strategies for very flexible aeroelastic systems are presented. They are underpinned by an aeroelastic model built from a one-dimensional intrinsic (based on strains and velocities) description of geometrically nonlinear beams and an unsteady vortex lattice aerodynamic model. Construction of a nonlinear modal-based reduced-order model of the aeroelastic system, employing a state-space realization of the linearized aerodynamics around an arbitrary reference point, allows us to capture the main nonlinear geometrical couplings at a very low computational cost. Embedding this model in both MHE and MPC strategies, which solve the system continuous-time adjoints efficiently to compute sensitivities, lays the foundations for real-time estimation and control of highly flexible aeroelastic systems. Finally, the performance and versatility of the framework operating in the nonlinear regime are demonstrated on two very flexible-wing models, with notably different dynamics, and on two different control setups: a gust-load alleviation problem on a very high-aspect-ratio wing with slower dynamics, which involves substantial deflections; and flutter suppression on a flexible wing with significantly faster dynamics, where an unconventional nonlinear stabilization mechanism is unveiled.

Observer based sliding mode control for subsonic piezo-composite plate involving time varying measurement delay

In this study, an observer based sliding mode control (SMC) scheme is proposed for vibration suppression of subsonic piezo-composite plate in the presence of time varying measurement delay by using the piezoelectric patch (PZT) actuator. Firstly, the state space form of the subsonic piezo-composite plate model is derived by Hamilton’s principle with the assumed mode method. Then an state observer involving time varying delay is constructed and the sufficient condition of the asymptotic stability is derived by using the Lyapunov-Krasovskii function, descriptor method and linear matrix inequalities (LMIs) for the state estimation error dynamical system. Subsequently, a sliding manifold is constructed on the estimation space. Then an observer-based controller is synthesized by using the SMC theory. The proposed SMC strategy ensures the reachability of the sliding manifold in the state estimate space. Finally, the simulation results are presented to demonstrate that the proposed observer-based controller strategy is effective in active aeroelastic control of subsonic piezo-composite plate involving time varying measurement delay.

The interaction between active aeroelastic control and structural tailoring in aeroservoelastic wing design

This paper presents an analysis of the interaction and trade-off between active aeroelastic control and passive structural tailoring on a free-flying fully flexible aircraft model. Both technologies are included in the preliminary design of a typical transport aircraft configuration with a conventional control surface layout containing trailing edge control surfaces and spoilers. The passive structural tailoring is facilitated by exploiting the anisotropic properties of composite materials to steer the static and dynamic aeroelastic behaviour. Active aeroelastic control is implemented by scheduled control surface deflections redistributing the aerodynamic loads during manoeuvres to achieve manoeuvre load alleviation and a feed-forward control law for gust load alleviation. The panel-based aerodynamic modelling of spoiler deflections is improved by a correction of the spatial distribution of the boundary condition derived from higher fidelity simulation data. The optimisation of active control laws requires the consideration of constraints of the actuation system, namely rate and deflection saturation, in a nonlinear manner. The interaction of manoeuvre load alleviation, gust load alleviation and passive structural tailoring is investigated on the basis of results of different aeroservoelastic optimisations. Therefore the primary wing structure is simultaneously optimised with the individual technologies being activated or deactivated, resulting in eight different wing structures. The results of the individual and combined optimisations reveal significant design differences. The potentials of the different technologies can only be optimally exploited by simultaneous optimisation. The paper concludes with a study of the sensitivity of the major findings with respect to the knockdown factor for failure applied to the material properties. A substantial shift of effectiveness from active aeroelastic control to passive structural tailoring is observed with increased allowables resulting in more flexible and hence less stiff wing designs.

Recent developments in the aeroelasticity of morphing aircraft

This paper presents an extensive review of the developments in the aeroelasticity of morphing aircraft that occurred in the last decade (from 2009 to 2020). It focuses mainly on fixed-wing aircraft and highlights some representative examples from rotary-wing aircraft. Morphing wings are usually associated with significant changes in the aerodynamic loads, structural/elastic properties, and inertial properties and hence the aeroelastic behavior. Changes in aeroelastic behavior can also affect the flight dynamics, stability, and control of air-vehicles. The main motivation for this paper is the fact that it is not fully possible to assess and quantify the benefits of morphing technologies without accounting for aeroelastic effects. The literature on the aeroelasticity of morphing aircraft can be split into two main themes: Aeroelastic Stability and Aeroelastic Control. The first theme (Aeroelastic Stability) includes studies conducted on morphing concepts to ensure that they satisfy certain aeroelastic requirements/constraints and that such requirements/constraints do not limit the potential benefits of morphing. The second theme (Aeroelastic Control) includes studies that utilized morphing technologies to improve aeroelastic characteristics and/or control flight loads. It is evident that in both themes, the aeroelasticity of morphing aircraft has been analyzed using analytical, numerical, and/or computational tools with a very limited number of wind-tunnel and/or flight tests. In this paper, research activities and studies are categorized according to the morphing degree of freedom they address. For each degree of freedom, research activities are arranged according to the theme they fit under. Aeroelastic frameworks developed for generic morphing applications are also reviewed. In addition, the aeroelastic models used are highlighted and discussed. Finally, trends and research gaps are identified and discussed and main conclusions are drawn.

Aeroelastic control of bridge using active control surfaces: Analytical and experiment study

An active control using a control surface system with winglets is described herein. Winglets help a long suspension bridge reach a stable state of flutter and buffeting. This system ensures the aerodynamic stability of a lightweight and economic stiffening girder without additional stiffening. Using a two-dimensional model, numerical and experimental studies were carried out to find a feedback control using winglets. In conclusion, a suitable control of the winglet motion can increase the flutter speed of a suspension bridge as the buffeting response moves in a contrasting manner.

Parametric active aeroelastic control of a morphing wing using the receptance method

This study proposes the parametric active aeroelastic control of a folding wing, which is a promising concept of morphing wings, by integrating the parameterized aeroservoelastic model and the receptance-based control strategy. It starts with establishing the parameterized aeroservoelastic model of the folding wing with respect to its folding angle and air speed. The transfer functions between the embedded sensors and the actuators of the folding wing are then efficiently obtained using the parameterized aeroservoelastic model. Finally, control gains for varying folding angle and air speed of the wing are synthesized using the receptance method. The results of numerical analyses show that smooth evolutions of the control gains can be obtained over a wide range of folding angles and air speeds, although the dynamic behavior of the folding wing is sensitive to these parameters. In addition, the active aeroelastic control can effectively suppress aeroelastic vibrations and expand flutter boundaries of the folding wing. The benefit of the parametric active aeroelastic control for the folding wing, i.e., smoothly switching among the control laws without exciting undesirable vibrations is highlighted.

Dynamic mode decomposition analysis of plasma aeroelastic control of airfoils in cascade

A dynamic mode decomposition (DMD) is carried out for the flow field in a compressor cascade with plasma actuators employed for aeroelastic control. Numerical assessments performed in previous works have shown that alternate triggering of pressure side/suction side actuators installed at the trailing edge of the blades can effectively reduce vibratory loads and enlarge the flutter boundaries of a linear compressor cascade. With the twofold aim of obtaining an in-depth understanding of the flow physics associated to plasma actuation and ultimately developing an optimized control law for the actuators, the dominant structures of the pressure field are extracted via a dynamic mode decomposition. The decomposition is conducted on the actuated and non-actuated pressure fields at several inter blade phase angles. The fundamental effects of plasma actuations on the flow field, and in turn on the blade loading, are identified and discussed. The procedure allows obtaining an useful picture of the main fluid mechanic phenomena associated to plasma aeroelastic control on turbomachinery blades. Additionally, the DMD spectrum and its coherence are analysed, yielding a wider energetic spread over high-order modes for the plasma-actuated case, in comparison to the clean cascade.