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1.
To investigate the flutter characteristics of a folding wing with different configurations, a parameterized aeroelastic model is proposed. First, a parameterized structural model is established based on the substructure synthesis. Afterwards, the parameterized aerodynamic model is derived for each lifting surface using the so-called Doublet Lattice Method (DLM). The correctness of the resulting aeroelastic model is verified via NASTRAN. Finally, some aeroelastic simulations are performed using the proposed aeroelastic model. The results demonstrate that the flutter characteristics of the folding wing are very sensitive to the folding angle. With increasing folding angle, a transition between two unstable modes occurs. Such a transition results in a sudden change of flutter mode shapes and a jump of critical flutter frequency. Besides, there exists a region of folding angle, where the flutter behavior of the folding wing strongly depends on the structural damping. 相似文献
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带有结构非线性的跨音速翼型颤振特性研究 总被引:1,自引:0,他引:1
以非定常N-S方程为主管方程,采用时间推进的方法,计算翼型振荡的瞬态非定常气动力,并与带有结构非线性的颤振方程耦合求解,计算了带有结构刚度非线性(间隙型,三次型刚度非线性)和结构阻尼非线性(三次型阻尼非线性)的结构响应特性和颤振特性.计算研究表明,由于同时具有结构和气动非线性,振荡极限环和气动力极为复杂. 相似文献
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S.D. Savkar 《Journal of sound and vibration》1976,46(2):195-207
The problem of a thin airfoil oscillating in a transonic flow duct is examined. Asymptotic solutions valid at high frequency are derived which suggest that the degree of interference from the tunnel walls is weaker than would be thought at first. More detailed calculations are then used to deduce the flutter characteristics of such airfoils. It is predicted that the airfoil will suffer a torsional mode instability for a range of parameters. 相似文献
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In this study, we consider a class of nonlinear aeroelastic stability problems, where geometric nonlinearities arising from large deflections and rotations in the structure interact with aerodynamic nonlinearities caused by moving shocks. Examples include transonic panel flutter and flutter of transonic wings of high aspect ratio, where the presence of both structural and aerodynamic nonlinearities can have a dramatic qualitative as well as quantitative effect on the flutter behavior. Both cases represent inherently nonlinear fluid-structure problems, where neglecting either the structural or the fluid nonlinearities can lead to completely erroneous stability predictions. The results presented in this paper illustrate the rich and in some cases surprising flutter behaviors of transonic wings, and the inherent limitations of the von Kármán nonlinear plate model in strongly nonlinear fluid-structure interaction problems of this type. 相似文献
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《Journal of sound and vibration》2004,269(3-5):669-687
Non-linear aeroelastic characteristics of a deployable missile control fin with structural non-linearity are investigated. A deployable missile control fin is modelled as a two-dimensional typical section model. Doublet-point method is used for the calculation of supersonic unsteady aerodynamic forces, and aerodynamic forces are approximated by using the minimum-state approximation. For non-linear flutter analysis structural non-linearity is represented by an asymmetric bilinear spring and is linearized by using the describing function method. The linear and non-linear flutter analyses indicate that the flutter characteristics are significantly dependent on the frequency ratio. From the non-linear flutter analysis, various types of limit cycle oscillations are observed in a wide range of air speeds below or above the linear divergent flutter boundary. The non-linear flutter characteristics and the non-linear aeroelastic responses are investigated. 相似文献
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Uncertainty analysis near bifurcation of an aeroelastic system 总被引:1,自引:0,他引:1
Variations in structural and aerodynamic nonlinearities on the dynamic behavior of an aeroelastic system are investigated. The aeroelastic system consists of a rigid airfoil that is supported by nonlinear springs in the pitch and plunge directions and subjected to nonlinear aerodynamic loads. We follow two approaches to determine the effects of variations in the linear and nonlinear plunge and pitch stiffness coefficients of this aeroelastic system on its stability near the bifurcation. The first approach is based on implementation of intrusive polynomial chaos expansion (PCE) on the governing equations, yielding a set of nonlinear coupled ordinary differential equations that are numerically solved. The results show that this approach is capable of determining sensitivity of the flutter speed to variations in the linear pitch stiffness coefficient. On the other hand, it fails to predict changes in the type of the instability associated with randomness in the cubic stiffness coefficient. In the second approach, the normal form is used to investigate the flutter (Hopf bifurcation) boundary that occurs as the freestream velocity is increased and to analytically predict the amplitude and frequency of the ensuing LCO. The results show that this mathematical approach provides detailed aspects of the effects of the different system nonlinearities on its dynamic behavior. Furthermore, this approach could be effectively used to perform sensitivity analysis of the system's response to variations in its parameters. 相似文献
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P. SHAHRZADM. MAHZOON 《Journal of sound and vibration》2002,256(2):213-225
The limit cycle flutter of a two-dimensional wing with non-linear pitching stiffness is investigated. For modelling the aerodynamic forces of the wing steady linear and non-linear models as well as an unsteady model were used. The flutter speed was calculated using the harmonic balance method and by predicting Hopf bifurcation. Analytical solutions based on the centre manifold theory and normal forms were obtained as were results given by the harmonic balance method. The analytical solutions were compared with those obtained by numerical integration. The results show that the harmonic balance method can forecast flutter speed with a good accuracy while analytical solutions based on centre manifold theorem are accurate only in a small neighbourhood of the bifurcation point. The oscillation of the airfoil after flutter for two different models, linear and non-linear pitching stiffness were compared with each other and the flutter speeds for two linear steady and an unsteady aerodynamic model calculated. The obtained results show that flutter analysis based on the linear steady model is conservative only for the ratios of plunge frequency to pitch frequency lower than 1. 相似文献
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We investigate the effects of parameter uncertainties on the dynamical response of an aeroelastic model representing an oscillating airfoil in pitch and plunge with linear aerodynamics and cubic structural nonlinearities. An approach based on the stochastic normal form is proposed to determine the effects due to the variations in the flow speed and the structural stiffness terms on the stability of the aeroelastic system near the Hopf bifurcation point. This approach allows us to study analytically the bifurcation scenario and to predict the amplitude and frequency of the limit cycle oscillation (LCO). The results show that the amplitude of LCO corresponding to the supercritical Hopf bifurcation increases with the intensity of the noise perturbing the pitch and plunge cubic terms, but there is almost no effect on the LCO frequency. Uncertainties in the flow speed produce a shift in the bifurcation point, and unstable subcritical behavior may occur for values of parameters for which the corresponding deterministic model is stable. The stochastic normal form confirms and extends previously known numerical results regarding the effect of parameter variations, and offers an effective way to perform sensitivity analysis of the system's response. 相似文献
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An adaptive stochastic spectral projection method is deployed for the uncertainty quantification in limit-cycle oscillations of an elastically mounted two-dimensional lifting surface in a supersonic flow field. Variabilities in the structural parameters are propagated in the aeroelastic system which accounts for nonlinear restoring force and moment by means of hardening cubic springs. The physical nonlinearities promote sharp and sudden flutter onset for small change of the reduced velocity. In a stochastic context, this behavior translates to steep solution gradients developing in the parametric space. A remedy is to expand the stochastic response of the airfoil on a piecewise generalized polynomial chaos basis. Accurate approximation andaffordable computational costs are obtained using sensitivity-based adaptivity for various types of supersonic stochastic responses depending on the selected values of the Mach number on the bifurcation map. Sensitivity analysis via Sobol' indices shows how the probability density function of the peak pitch amplitude responds to combined uncertainties: e.g. the elastic axis location, torsional stiffness and flap angle. We believe that this work demonstrates the capability and flexibility of the approach for more reliable predictions of realistic aeroelastic systems subject to a moderate number of uncertainties. 相似文献
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Aeroelastic dynamic response and control of an airfoil section with control surface nonlinearities 总被引:1,自引:0,他引:1
Nonlinearities in aircraft mechanisms are inevitable, especially in the control system. It is necessary to investigate the effects of them on the dynamic response and control performance of aeroelastic system. In this paper, based on the state-dependent Riccati equation method, a state feedback suboptimal control law is derived for aeroelastic response and flutter suppression of a three degree-of-freedom typical airfoil section. With the control law designed, nonlinear effects of freeplay in the control surface and time delay between the control input and actuator are investigated by numerical approach. A cubic nonlinearity in pitch degree is adopted to prevent the aeroelastic responses from divergence when the flow velocity exceeds the critical flutter speed. For the system with a freeplay, the responses of both open- and closed-loop systems are determined with Runge-Kutta algorithm in conjunction with Henon’s method. This method is used to locate the switching points accurately and efficiently as the system moves from one subdomain into another. The simulation results show that the freeplay leads to a forward phase response and a slight increase of flutter speed of the closed-loop system. The effect of freeplay on the aeroelastic response decreases as the flow velocity increases. The time delay between the control input and actuator may impair control performance and cause high-frequency motion and quasi-periodic vibration. 相似文献
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The Unsteady Adaptive Stochastic Finite Elements (UASFE) method resolves the effect of randomness in numerical simulations of single-mode aeroelastic responses with a constant accuracy in time for a constant number of samples. In this paper, the UASFE framework is extended to multi-frequency responses and continuous structures by employing a wavelet decomposition pre-processing step to decompose the sampled multi-frequency signals into single-frequency components. The effect of the randomness on the multi-frequency response is then obtained by summing the results of the UASFE interpolation at constant phase for the different frequency components. Results for multi-frequency responses and continuous structures show a three orders of magnitude reduction of computational costs compared to crude Monte Carlo simulations in a harmonically forced oscillator, a flutter panel problem, and the three-dimensional transonic AGARD 445.6 wing aeroelastic benchmark subject to random fields and random parameters with various probability distributions. 相似文献
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It is shown that the equations of motion of an aeroelastic system may be derived from measured response data. The structural and aerodynamic terms are separated by analyzing response measurements at two values of kinetic pressure; the derived equations can then be used to calculate dynamic characteristics of the system at any chosen values of kinetic pressure. Two examples of the application of the analysis to the prediction of flutter characteristics are given. 相似文献
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Chaotic motions of a two dimensional airfoil with coupled structural nonlinearities, both in pitch as well as plunge degrees of freedom, are investigated via a numerical integration method. The original system of coupled integro-differential equations governing the motion of the present aeroelastic model is transformed into a simple system of six ordinary differential equations (ODEs), rather than the previously frequently used eight ODEs. Complex dynamical behaviors are revealed and identified through the means of bifurcation diagrams, the phase portraits, the amplitude spectra and the Poincare maps. Besides, a more quantitative method, namely that of observing the evolution of the largest Lyapunov exponent (LLE) is also applied to diagnose the motions. Two peculiar phenomena, namely, long (perhaps super-persistent) chaotic transients, and fluctuating Lyapunov exponents, are observed; in the two such cases the LLE method fails to work. In addition, the effects of various system parameters, namely, the position of the elastic axis, the frequency ratio, the airfoil/air mass ratio, the viscous damping ratios, and the location of the center of mass, on the response of the aeroelastic system, are investigated. 相似文献
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The dynamic behaviors of multi-layer sandwich beams are investigated through single degree-of-freedom (SDOF) transformation. The frequency response of the multi-layer sandwich beam is obtained using finite element code COMSOL and is transformed to a SDOF system with the same frequency response. Hence, the mass, spring constant and damping coefficient of the sandwich beams with different lengths and number of visco-elastic layers can be investigated. Further, viscous damping and structural damping models are individually employed to simulate the damping effect of the sandwich beam. The frequency responses from both models are compared with that from COMSOL and experiment. The resonant peak and resonant frequency of the SDOF system using structural damping model is more consistent with that from COMSOL. The experimental result demonstrates that the response of the sandwich beam can be predicted through COMSOL and SDOF transformation. 相似文献
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Liviu Librescu Sungsoo Na Zhanming Qin Bokhee Lee 《Journal of sound and vibration》2008,318(1-2):74-92
In this paper, the dynamic aeroelastic response and the related robust control of aircraft swept wings exposed to gust and explosive type loads are examined. The structural model of the wing is in the form of a thin/thick-walled beam and incorporates a number of non-standard effects, such as transverse shear, material anisotropy, warping inhibition, the spanwise non-uniformity of the cross-section, and the rotatory inertias. The circumferentially asymmetric stiffness lay-up configuration is implemented to generate preferred elastic couplings, and in this context, the implications of the plunging–twist elastic coupling and of warping inhibition on the aeroelastic response are investigated. The unsteady incompressible aerodynamic theory adopted in this study is that by von-Kármán and Sears, applicable to arbitrary small motion in the time domain. The considered control methodology enabling one to enhance the aeroelastic response in the subcritical flight speed range and to suppress the occurrence of the flutter instability is based on a novel control approach that is aimed to improve the robustness to modeling uncertainties and external disturbances. To this end, a combined control based on Linear Quadratic Gaussian (LQG) controller coupled with the Sliding Mode Observer (SMO) is designed and its high efficiency is put into evidence. 相似文献
20.
Bifurcation and chaos analysis for aeroelastic airfoil with freeplay structural nonlinearity in pitch
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The dynamics character of a two degree-of-freedom
aeroelastic airfoil with combined freeplay and cubic stiffness
nonlinearities in pitch submitted to supersonic and hypersonic flow
has been gaining significant attention. The Poincaré mapping
method and Floquet theory are adopted to analyse the limit cycle
oscillation flutter and chaotic motion of this system. The result
shows that the limit cycle oscillation flutter can be accurately
predicted by the Floquet multiplier. The phase trajectories of both
the pitch and plunge motion are obtained and the results show that
the plunge motion is much more complex than the pitch motion. It is
also proved that initial conditions have important influences on the
dynamics character of the airfoil system. In a certain range of
airspeed and with the same system parameters, the stable limit cycle
oscillation, chaotic and multi-periodic motions can be detected
under different initial conditions. The figure of the Poincaré
section also approves the previous conclusion. 相似文献