Nonlinear Aeroelastic Effects Research Articles

Predicting crosswind response of tall buildings: Base isolation and nonlinear aeroelastic effects

This study introduces an analysis framework to evaluate the crosswind response of tall buildings under the influence of base isolation and nonlinear aeroelastic effect near the vortex lock-in wind speed. The motion-induced and buffeting forces are determined based on those in a building with a fixed base. The primary focus is on modeling the motion-induced force in tall buildings with base isolation, where no pre-existing model exists. The fundamental modal displacement is used to describe the building motion relative to the base. The Bouc-Wen model is employed to capture the hysteresis in the relation of shear force and displacement of the isolation system. Through response history analysis, the response statistics of a 65-story building with a square cross-section are determined and compared with those of a fixed-base building. An investigation is conducted to examine the impact of different isolation layer parameters on building response. Additionally, this study explores how the motion-induced force model influences the building response. The findings indicate that base isolation effectively mitigates nonlinear aeroelastic effects, leading to a significant reduction in crosswind response.

Stall nonlinear aeroelastic effects and active control of thin-walled composite blade with piezoelectric patches embedded

Stall nonlinear flutter behavior and active control of anisotropic composite blade have been investigated based on piezoelectric actuation. The blade body comprises an elliptical composite host structure and a lightweight honeycomb skin structure. The composite blade with elliptical section is modeled as a thin-walled beam structure with circumferential asymmetric stiffness (CAS) configuration, exhibiting transverse shear deformation, warping restraint effect, and vertical bending, with structural tailoring implemented. The stall-induced flutter suppression and nonlinear aeroelastic effects of linearized dynamic response characteristics of blade incorporating stall nonlinear aerodynamic model are investigated. The nonlinear aeroelastic coupled equations are reduced to ordinary equations by the Galerkin method, with the aerodynamic force decomposed by strip theory. Active feedback control based on boundary moment control strategy is developed to enhance the vibrational behavior and dynamic response to aerodynamic excitation and stabilize structures that might be damaged in the absence of control. Various active feedback control schemes tuned by optimal proportional-derivative (PD) controller are implemented. The excellent control effect is not only confirmed by the time response with its vibration amplitude greatly suppressed but also confirmed by the frequency change and comparison. The research provides a way for rare study of amplitude suppression of stall nonlinear aeroelastic effect of thin-walled composite blade with CAS configuration and piezoelectric patches embedded.

Application scope of equivalent linear technique for across-wind response analysis of tall flexible structures considering nonlinear aero-elastic effect

Large across-wind response of tall flexible structures becomes an increasing concern due to the significant nonlinear aero-elastic effect. The nonlinear aerodynamic damping, which is in phase of time-variant structural velocity, is usually employed to describe nonlinear aero-elastic effect. For the sake of evaluating the across-wind response of tall flexible structures within the framework of linear random vibration theory, equivalent linear aerodynamic damping model is required, which can be deduced from either harmonic balance (HB)- or statistical linearization (SL) technique. This study addressed clarifying application scope of various equivalent linear techniques for evaluating across-wind response of tall flexible structures. By conducting the Monte Carlo simulation and free-vibration wind tunnel test, it is clarified that the root-mean-squared (RMS) response calculated by the HB equivalent linear aerodynamic damping is acceptable, while is not satisfactory with respect to the SL technique especially when the structure is with lower damping level, and in the vicinity of vortex lock-in wind speed. Moreover, it is found that neither HB- nor SL technique can accurately predict the peak response. It is revealed in this study that accuracy of various equivalent linear techniques is essentially affected by probability density function of across-wind response.

Geometrically Nonlinear Effects on the Aeroelastic Response of a Transport Aircraft Configuration

This paper investigates geometrically nonlinear aeroelastic effects on an industry-level aircraft configuration. Results are obtained via a new approach that uses geometrical information to compute nonlinear effects and seamlessly integrates with conventional, linear aeroelastic load packages. The starting point is a generic finite-element model and frequency-domain aerodynamic influence coefficient matrices, and the resulting system includes control inputs, longitudinal trim, or gust disturbances in time domain, which can be employed separately or in combination to obtain a nonlinear dynamic model for loads and stability analysis. The aeroelastic response of a long range aircraft is studied, highlighting the difference between linear and nonlinear approaches in the calculations of the aircraft flying equilibrium, dynamic perturbations, and variations to the flutter boundary. Results justify the need for geometrically nonlinear analysis in the production environment of airplanes with ultrahigh-aspect-ratio wings.

Numerical investigation on the nonlinear flutter behaviors of a π-shaped sectional bridge deck

Nonlinear flutter behaviors of a π-shaped sectional bridge deck are investigated numerically, focusing on the effects on the post-flutter limit cycle oscillation (LCO) amplitudes caused by various nonlinearities, including aeroelastic, structural damping, and geometric nonlinearity. The Multi-stage indicial functions (IFs) are adapted to describe the nonlinear aeroelastic effects in time-domain, which necessitate amplitude-dependent aeroelastic model parameters. The motion amplitude-dependent parameters are mainly extracted numerically with computational fluid dynamics (CFD) method and partially examined by experimentally extracted results. The CFD-based parameters turn out to be satisfactory compared with experimental results. Finally, the flutter thresholds and post-flutter limit cycle oscillations are simulated using the present time-domain multi-stage indicial functions model. The numerical results show that introduction of any one kind of nonlinearity (aeroelastic, structural damping, or geometric) in the numerical procedure can lead to LCO. These three kinds of nonlinearity are compared in detail in terms of the effects they have on the post-flutter LCO amplitude. It turns out that the damping nonlinearity, for the case concerned in this work, is the most important factor that determines the post-flutter LCO amplitude and the flutter onset wind speed as well. The time-domain multi-stage indicial functions procedure adopted in this work can serve as an efficient solving strategy to obtain nonlinear post-flutter performances of long-span bridges.

Tuned mass damper for self-excited vibration control: Optimization involving nonlinear aeroelastic effect

The conventional target for self-excited galloping/flutter control of a civil structure often focuses on the critical wind speed. In the present work, a nonlinear control target is introduced, i.e., to ensure that the vibration amplitude is lower than a threshold value (pre-specified according to the expected structural performance) before a target wind speed. Unlike the conventional control target, the nonlinear one can take into account the underlying large-amplitude vibrations before the critical state and/or the structural safety redundancy after the critical state. To obtain the most economical TMD parameters that enable the nonlinear target, an optimization procedure involving nonlinear aeroelastic effect is developed for galloping control based on the quasi-steady aeroelastic force model, and for flutter control based on a nonlinear unsteady model. Three numerical examples involving the galloping/flutter control of different cross-sections are analyzed to demonstrate the different results designed by the conventional and nonlinear targets. It is demonstrated that the nonlinear target and optimization procedure can lead to more economical design results than the conventional ones in the galloping/flutter control for a structure with relatively large post-critical safety redundancy, and they are more reliable than the conventional ones for a structure that may experience large-amplitude vibrations before the critical wind speed. These superiorities of the nonlinear control target and new optimization procedure suggest that they may be utilized in the TMD parameter optimization for galloping/flutter control of structures in a wide domain of engineering fields.

Parameterized Fictitious Mode of Morphing Wing with Bilinear Hinge Stiffness

As a typical morphing wing, a folding wing with structural nonlinearities may encounter complex nonlinear aeroelastic effects during the in-flight morphing process. This paper presents a novel parameterized modeling methodology for efficient modal and nonlinear aeroelastic analysis of a folding wing with bilinear hinge stiffness and the variation of the folding angle. The most attractive feature of the present modeling methodology is that the nonlinear structural dynamics of the folding wing at different folding angles can be efficiently represented via a parameterized fictitious mode. To demonstrate the accuracy of the present method in representing the nonlinear dynamics of the morphing wing, a folding wing with bilinear stiffness in both fuselage–inboard and inboard–outboard hinges was selected as a numerical example. The nonlinear dynamic model of the selected example can be divided into nine subsystems according to different combinations of fuselage–inboard and inboard–outboard hinge stiffness. This paper focuses on the efficient investigation of structural modes, flutter stability, and nonlinear aeroelastic behaviors of the folding wing at the complete morphing parameter space. Besides, the numerical results computed via the present parameterized fictitious mode method were also compared with the direct commercial software. The comparison shows that the nonlinear dynamics of the morphing wing with bilinear hinge stiffness can be investigated efficiently via the present parameterized modeling method.

Gradient-Based Optimization of Solar-Regenerative High-Altitude Long-Endurance Aircraft

This paper uses gradient-based optimization to minimize the mass of a solar-regenerative high-altitude long-endurance flying-wing aircraft while accounting for nonlinear aeroelastic effects. The aircraft is designed to fly year round at 35° latitude at 18 km above sea level and subjected to energy capture, energy storage, material failure, local buckling, stall, longitudinal stability, and coupled flight and aeroelastic stability constraints. The optimized aircraft has an aspect ratio of 54.52, a surface area of , a mass of 349.5 kg; exhibits little aeroelastic deflection at the design airspeed; and is primarily stability constrained. Several parameter sweeps are performed to determine sensitivity to altitude, latitude, battery specific energy, solar efficiency, avionics and payload power requirements, and minimum design velocity.

Nonlinear Aeroelastic in-Plane Behavior of Suspension Bridges under Steady Wind Flow

The nonlinear aeroelastic behavior of suspension bridges, undergoing dynamical in-plain instability (galloping), is analyzed. A nonlinear continuous model of bridge is formulated, made of a visco-elastic beam and a parabolic cable, connected each other by axially rigid suspenders, continuously distributed. The structure is loaded by a uniform wind flow which acts normally to the bridge plane. Both external and internal damping are accounted for the structure, according to the Kelvin-Voigt rheological model. The nonlinear aeroelastic effects are evaluated via the quasi-static theory, while structural nonlinearities are not taken into account. First, the free dynamics of the undamped bridge are addressed, and the natural modes determined. Then, the nonlinear equations ruling the dynamics of the aeroelastic system, close to the bifurcation point, are tackled by the Multiple Scale Method. This is directly applied to the partial differential equations, and provides the finite-dimensional bifurcation equations. From these latter, the limit-cycle amplitude and its stability are evaluated as function of the mean wind velocity. A case study of suspension bridge is analyzed.

Evaluation of time-domain damping identification methods for flutter-constrained optimization

As engineers increasingly pursue air vehicle designs with slender, lightweight aerostructures, it has become necessary to model nonlinear aeroelastic effects earlier in the design process. As a result, high-fidelity analysis tools are required that can efficiently identify flutter within the flight envelope, and find design modifications to alleviate adverse aeroelastic behavior. To address these requirements, we have systematically evaluated automated methods to identify the damping of an aeroelastic system from a time-domain simulation. The techniques evaluated include the log decrement method, envelope function methods that use the Hilbert transformation, the half-power bandwidth method, and the matrix pencil method. The optimal approach was determined to be the matrix pencil method due to its robustness to noise and its ability to handle multi-component signals over short time simulations. Identification of the flutter boundary of the AGARD-445.6 wing is demonstrated with an automated method based on the adjoint sensitivities and the matrix pencil method. While the matrix pencil method is robust, identification of the flutter boundary using gradient-based optimization is shown to be sensitive to the initial dynamic pressure guess.

Using tuned mass damper inerter to mitigate vortex-induced vibration of long-span bridges: Analytical study

The undesirable vortex-induced vibration (VIV) may seriously influence the fatigue life and serviceability of bridge structures. It is important to take countermeasures to suppress the adverse VIV of long-span bridges. In the present study, a novel inerter-based system, namely the tuned mass damper inerter (TMDI), is proposed to control the VIV of the main deck of long-span bridges. In this system, an inerter device, which is able to transform the linear motion into the high-speed rotational motion and thus significantly amplifies the physical mass of the system, is incorporated into the conventional tuned mass damper (TMD) system to further improve the performance of TMD. An applicable layout of the TMDI inside the bridge deck is introduced and the governing equations of the structure-TMDI system subjected to VIV are established. The optimization of the TMDI parameters with the consideration of nonlinear aeroelastic effect is derived. The control performance and robustness of the proposed system are investigated through an analytical case study in both the time and frequency domains. It is observed that the TMDI system can obviously reduce the VIV responses of the bridge deck. Moreover, compared to the conventional TMD system, the static stretching of the spring due to gravity and the oscillation amplitude of the mass block in the TMDI system are significantly reduced. These properties make the proposed TMDI system an attractive alternative for the VIV control of long-span bridges.

Estimation of Nonstationary Crosswind Response of Tall Buildings with Nonlinear Aeroelastic Effect

AbstractThis study addresses analysis of the crosswind response of tall buildings under nonstationary wind excitations. The wind load under nonstationary wind excitation was quantified using the fo...

Erratum for “Extreme Value Distribution and Peak Factor of Crosswind Response of Flexible Structures with Nonlinear Aeroelastic Effect” by Xinzhong Chen

Erratum for “Extreme Value Distribution and Peak Factor of Crosswind Response of Flexible Structures with Nonlinear Aeroelastic Effect” by Xinzhong Chen

Research on the Geometry Nonlinearity of Wind Turbine Blade

It is presented that the nonlinear aeroelastic effect is considered for the dynamic response analysis of large scale horizontal wind turbine. The blade of wind turbine is built by composite laminate model using the finite element method. The unsteady aerodynamic loads are predicted with prescribed vortex wake method, which considers the aerodynamic-structural coupling effects. The aerodynamic loads are applied to the blade structure model, and the nonlinear dynamic aeroelastic equations are established. The equations are linearized and the blade modes are obtained at the static equilibrium position, thus the dynamic responses of a blade are calculated using the modal method. The results show that the geometry nonlinearity reduces the vibration amplitudes of the blade.

Extreme Value Distribution and Peak Factor of Crosswind Response of Flexible Structures with Nonlinear Aeroelastic Effect

The crosswind response at the vicinity of vortex lock-in wind speed becomes an increasing concern in structural design of super tall buildings and other dynamically sensitive structures. Because of nonlinear aeroelastic effect of vortex shedding, the extreme value distribution and peak factor of crosswind response are distinctly different from traditional wind-induced stochastic buffeting response. This study establishes an effective approach for predicting extreme value distribution and peak factor of crosswind response of flexible structures on the basis of an improved understanding of the underlying mechanism. It is pointed out that the improved extreme theory of Gaussian processes with consideration of narrow-band feature cannot interpret the extreme crosswind response. This study, at the first time, reveals that the unique characteristics of extreme value distribution of crosswind response is primarily attributed to its hardening non-Gaussian distribution. An extensive analysis of simulated crosswind response illustrates that the extreme value distribution and peak factor can be estimated from those of an underlying Gaussian process based on the translation process theory. The translation function between non-Gaussian crosswind response and Gaussian process can be expressed in terms of Hermite polynomial model based on the first four statistical moments or quantified by mapping of cumulative distribution functions and curve fitting. Closed-form formulations are developed for calculating Hermite translation model coefficients, which permits the estimation of extreme value distribution and peak factor directly using the response kurtosis and bandwidth parameter. The characteristics of crosswind response and the proposed approach are also validated using full-scale vibration measurements of a wind-excited traffic-signal-support structure. This study not only clarified the mechanism responsible for the unique extreme value distribution of crosswind response with nonlinear aeroelastic effect but also established an effective simple approach for its estimation using the characteristics of response process.

Estimation of extreme value distribution of crosswind response of wind-excited flexible structures based on extrapolation of crossing rate

This paper presents an approach based on response crossing rate analysis for estimating extreme value distribution of crosswind response of wind-excited structures with significant nonlinear aeroelastic effect. The crossing rates at various thresholds are calculated from response time histories, and are then curve-fitted by a prescribed parametric model. The influence of narrow band characteristic of response is accounted by using envelope process with two-state description of crossings and a further consideration of mean clump size. The curve-fitting and extrapolation of crossing rate permit estimation of extreme value distribution using Poisson distribution of crossings. The effectiveness and accuracy of the approach are examined using simulated crosswind responses covering a wide range of non-Gaussian characteristics, and also using full-scale vibration measurement data of a wind-excited traffic-signal-support structure. The results illustrated that the approach can produce robust estimations of extreme value distributions of hardening non-Gaussian crosswind responses. The narrow band characteristic of response process has very limited effect on the extremes of hardening non-Gaussian responses. The approach presented is especially effective in practice, where the number of available response time histories is often very limited, and a direct use of extreme samples fails to provide accurate estimation of extreme statistics.

Support-Vector-Machine-Based Reduced-Order Model for Limit Cycle Oscillation Prediction of Nonlinear Aeroelastic System

It is not easy for the system identification-based reduced-order model (ROM) and even eigenmode based reduced-order model to predict the limit cycle oscillation generated by the nonlinear unsteady aerodynamics. Most of these traditional ROMs are sensitive to the flow parameter variation. In order to deal with this problem, a support vector machine- (SVM-) based ROM was investigated and the general construction framework was proposed. The two-DOF aeroelastic system for the NACA 64A010 airfoil in transonic flow was then demonstrated for the new SVM-based ROM. The simulation results show that the new ROM can capture the LCO behavior of the nonlinear aeroelastic system with good accuracy and high efficiency. The robustness and computational efficiency of the SVM-based ROM would provide a promising tool for real-time flight simulation including nonlinear aeroelastic effects.

Design of morphing winglets with the inclusion of nonlinear aeroelastic effects

AbstractA nonlinear aeroelastic model capable of assessing arbitrary morphing manoeuvres and calculating the associated morphing energy requirement is presented in this paper. The aeroelastic model consists of a close coupling between a corotational beam element, accounting for geometric nonlinearities, and a Weissinger method aerodynamic model, containing the Prandtl-Glauert correction for high-subsonic Mach numbers. The morphing deformations are discretised into three distinct morphing modes; fold morphing, twist morphing, and shear morphing, because of which virtually any morphed shape can be achieved, given a proper distribution of the three modes over the wing. The proposed aeroelastic morphing framework is used to design morphing winglets, and it has been shown that morphing winglets can improve the performance of fixed winglets significantly for regional airliners.

Aerodynamic instability of a bridge deck section model: Linear and nonlinear approach to force modeling

The aerodynamic behavior of a bridge deck section model with a simple single-box shape was characterized in wind tunnel. At large nose-up mean angles of attack, a torsional instability arises, outlining a situation in which nonlinear aeroelastic effects may be critical. Such condition represents an interesting case to develop and validate nonlinear models for the aeroelastic problem. The experimental campaign allowed both to characterize the aerodynamic forces using forced motion tests and to study the aeroelastic behavior of the section model, when excited by actively generated turbulent wind. These aeroelastic tests are used to validate a numerical time-domain model for aerodynamic forces that takes into account the nonlinearities due to the reduced velocity and to the amplitude of the instantaneous angle of incidence. Results are critically analyzed and compared with those obtained with a linear model.

Analytical and experimental modelling of non-linear aeroelastic effects on prismatic bodies

This paper deals with the aeroelastic instability and non-linear post-critical behaviour of a two degree-of-freedom oscillatory system. The main goal of the study is an introduction of a realistic non-linear theoretical model making possible a detailed non-linear analysis of post-critical states of an aeroelastic system. Two component self-induced vibration of a body is described by a system of two simultaneous non-linear differential equations. The coupling of the resultant motion is due to linear and non-linear aeroelastic effects only, while the elastic forces are taken independent. Differential system is auto-parametric and represents a combination of Rayleigh or Van der Pol with Duffing types of differential equations. The qualitative analysis is based on the uplift coefficients and torsional moments as the functions of the flow velocity and structural response components. The effects of non-linearities are tested on the model where the motion of one degree of freedom is prevented. The analysis is verified experimentally by the new generation technique allowing excessive amplitudes of the oscillation.