Intermittency in a cantilever plate in a randomly fluctuating fluid flow

Fluid–elastic systems nearing dynamic instabilities are known to be sensitive to fluctuations in fluid flow. A cantilever plate in axial flow with random temporal fluctuations, is examined numerically for its dynamical behaviour. The numerical model comprises of a nonlinear structural model for the flexible plate, coupled with unsteady lumped vortex model for the fluid forces. As the mean flow velocity is increased, the system transitions to limit cycle oscillations from a state of rest, through a regime of intermittent oscillations. The conditions for onset and disappearance of intermittency are discussed and are interpreted using stochastic bifurcation theories. While the onset of intermittency is found to be unaffected by the time scales of the flow fluctuations, they are observed to affect the length of the intermittency regime. The effect of plate flexibility on intermittency is also discussed.     

High-frequency plate flutter

Earlier, using the global instability method, the stability of a strip plate in a supersonic gas flow was investigated. In addition to the classical (low-frequency) flutter developing upon the interaction between the plate oscillation modes, a novel (high-frequency) flutter type in which the oscillations are unimodal was detected. In the present study, the effect on the high-frequency flutter of the plate width (earlier only an asymptotic analysis for a width tending to infinity was performed), its damping characteristics, and the presence of a gas at rest on the side opposite the flow is investigated.     

Asymptotic analysis of aircraft wing model in subsonic air flow

This paper is the first in a series of several works devotedto the asymptotic and spectral analysis of an aircraft wingin a subsonic air flow. This model has been developed in theFlight Systems Research Center of UCLA and is presented in theworks of Balakrishnan. The model is governed by a system oftwo coupled integro-differential equations and a two parameterfamily of boundary conditions modelling the action of the self-strainingactuators. The unknown functions (the bending and the torsionangle) depend on time and one spatial variable. The differentialparts of the above equations form a coupled linear hyperbolicsystem; the integral parts are of convolution type. The systemof equations of motion is equivalent to a single operator evolution–convolutiontype equation in the state space of the system equipped withthe so-called energy metric. The Laplace transform of the solutionof this equation can be represented in terms of the so-calledgeneralized resolvent operator. The generalized resolvent operatoris an operator-valued function of the spectral parameter. Thisgeneralized resolvent operator is a finite meromorphic functiondefined on the complex plane having the branch cut along thenegative real semi-axis. The poles of the generalized resolventare precisely the aeroelastic modes, and the residues at thesepoles are the projectors on the generalized eigenspaces. Inthis paper, our main object of interest is the dynamics generatorof the differential parts of the system. It is a non-selfadjointoperator in the state space with a pure discrete spectrum. Inthe present paper, we show that the spectrum consists of twobranches, and we derive their precise spectral asymptotics.Based on these results, in the next paper we will derive theasymptotics of the aeroelastic modes and approximations forthe mode shapes.     

利用N-S方程模拟机翼气动弹性的一种计算方法

利用一种双时间方法求解三维非定常N-S方程,得到与任意非定常运动对应的气动力,在求解非定常气动力的同时,在时间域内用二阶龙格 库塔方法求解机翼弹性运动方程,从而模拟粘性流动中的气动弹性全过程.为保证网格生成效率,采用无限插值理论生成O-H型代数网格,考虑了机翼变形时的网格生成问题,并得到计算结果.     

多自由度强非线性颤振分析的增量谐波平衡法

对多个自由度上含有强非线性项系统的颤振问题,推广应用增量谐波平衡法进行分析．考虑带有强非线性立方平移和俯仰刚度项的二元机翼颤振方程,首先将方程用矩阵形式表示,然后把振动过程分解成为振动瞬态的持续增量过程,再采用振幅作为控制参数应用谐波平衡法,以这种推广的增量谐波平衡法求得方程解的表达式,并由此分析系统的分岔现象、极限环颤振现象和谐波项数的取值问题,最后用龙格-库塔数值方法进行验算,结果表明:分析多个自由度的强非线性颤振,增量谐波平衡法是精确有效的．     

Flutter of a Wide Strip Plate in a Supersonic Gas Flow

The stability of an elastic plate in the form of a wide strip in a supersonic inviscid gas flow is investigated in the linear approximation. An expression for the dependence of the pressure on the plate deflection, asymptotically exact for wide plates, is used. Two qualitatively different instability types are obtained: flutter with respect to a single oscillatory mode due to negative aerodynamic damping and flutter of a related type due to the interaction of oscillatory modes. For each type the stability criterion and the frequency at which the oscillation amplitude grows most intensely are found.     

Numerical Analysis of the Nonlinear Flutter of Viscoelastic Plates

The flutter velocities of viscoelastic plates are determined. It is shown that the viscoelastic characteristics reduce them__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 5, pp. 91–96, May 2005.     

INCREMENTAL HARMONIC BALANCE METHOD FOR AIRFOIL FLUTTER WITH MULTIPLE STRONG NONLINEARITIES

The incremental harmonic balance method was extended to analyze the flutter of systems with multiple structural strong nonlinearities. The strongly nonlinear cubic plunging and pitching stiffness terms were considered in the flutter equations of two-dimensional airfoil. First, the equations were transferred into matrix form, then the vibration process was divided into the persistent incremental processes of vibration moments. And the expression of their solutions could be obtained by using a certain amplitude as control parameter in the harmonic balance process, and then the bifurcation, limit cycle flutter phenomena and the number of harmonic terms were analyzed. Finally, numerical results calculated by the Runge-Kutta method were given to verify the results obtained by the proposed procedure. It has been shown that the incremental harmonic method is effective and precise in the analysis of strongly nonlinear flutter with multiple structural nonlinearities.     

采用分布式压电驱动器升力面的颤振主动抑制

对采用分布式压电驱动器升力面的颤振主动抑制进行了理论与试验研究.应用 LQG最优控制法设计了主动控制律,在控制律降阶时提出了平衡实现与LK法结合使用的新途径,在对不定常气动力进行有理函数拟合时对LS法进行了改进.试验中利用激光测速仪非接触测量模型的速度响应并在地面共振试验中用压电驱动器激振模型.颤振风洞试验结果表明,理论计算合理并与试验结果吻合良好.     

飞行器非线性气动弹性和颤振主动控制研究进展

首先，针对发展性能先进的新一代飞行器所涉及到的非线性气动弹性理论与分析技术，结合国内外研究进展情况，着重从建模技术、求解方法、非线性气弹特性分析几个方面进行概括总结。其次，对在飞行器设计中一直颇受关注的、智能材料在飞行器结构颤振及振动主动控制中应用研究现状也给予简要的介绍。最后指出一些尚待进一步研究的问题。