层合复合材料壁板的热颤振特性分析

采用壁板颤振分析的有限元方法,从壁板的正则化弯曲刚度、屈曲临界温升、颤振临界速压和极限环颤振幅值等参数的角度,分析了不同铺层方向和不同铺层顺序对层合复合材料壁板的颤振特性的影响,并给出了几种常见铺层方式层合复合材料壁板的颤振特性。结果表明,在设计复合材料壁板的铺层方向和铺层顺序时,一般可以通过壁板正则化弯曲刚度的大小来对颤振速压进行比较。但是在某些特殊的铺层情况下,随着温度升高,发生频率重合型颤振的耦合模态会发生演变,这时正则化弯曲刚度较大的壁板也有可能在较低的速压下发生颤振。     

基于POD降阶方法的复合材料曲壁板颤振响应特性研究

建立了三维复合材料曲壁板的气动弹性有限元方程,将本征正交分解方法(POD)应用于三维复合材料曲壁板的非线性颤振响应降阶分析中,通过POD方法构造三维复合材料曲壁板颤振响应的POD模态,然后将系统的运动方程变换到POD模态坐标下,通过数值积分方法计算三维复合材料曲壁板的颤振响应,与传统的模态缩减法计算结果相比,结果很好的吻合,且大大节省了计算时间。     

吸振夹层壁板颤振抑制的吸振器频率设计

摘 要：为了完善在夹层壁板的芯层安装微型动力吸振器来抑制壁板颤振这一新方案,研究了吸振夹层壁板中悬臂梁式动力吸振器的频率设计方法。基于壁板颤振的模态耦合机理,分别以单频率设计和双频率设计原则来确定吸振夹层壁板的吸振器频率。结果表明,所有微型吸振器按单频率设计时,存在一个不等于原夹层壁板颤振耦合模态频率和颤振频率的吸振器最佳设计频率,使得吸振夹层壁板的颤振速度最大;微型吸振器按双频率设计时,吸振夹层壁板的最大颤振速度远大于按单频率设计的最大颤振速度。     

非均衡铺层壁板复合材料机翼气动弹性分析

对上下壁板采用非均衡铺层的大展弦比复合材料机翼进行了气动弹性分析。建立了不同掠角和壁板铺层非均衡程度的气动弹性模型 , 并考虑了壁板铺层非均衡程度的变化。分析了严重载荷情况下 , 机翼变形、 升力特性弹性修正等随壁板铺层非均衡程度的变化 , 并分析了固有振动特性和发散/颤振速度随壁板铺层非均衡程度的变化趋势 , 以期为进行这类结构的设计提供参考。研究结果表明 : 壁板铺层的非均衡程度对于所研究机翼的固有振动频率、 颤振速度影响较小 , 但对发散速度和机翼的静气动弹性性能影响较大。      

气流偏角对不同形状复合材料壁板热颤振特性的影响

应用有限元方法分析研究了气流偏角和热载荷对不同形状复合材料壁板颤振特性的影响。采用一阶剪切理论、von Karman大变形板理论以及考虑气流偏角的一阶活塞气动力理论建立了考虑热载荷的复合材料壁板颤振的有限元模型。分析了三种面积相同但形状不同的复合材料壁板的颤振临界速压随温升和气流偏角的变化规律。结果表明,气流偏角为零时,面积相同形状不同的三种复合材料壁板的颤振临界速压随温度升高而近似呈线性降低,且三角形壁板的颤振临界速压高于梯形壁板,梯形壁板高于矩形壁板;随着气流偏角的增大,三种不同形状壁板的颤振临界速压都呈现出相同的规律;相同气流偏角下,三角形壁板的颤振临界速压最高,矩形壁板的颤振临界速压最低。     

三维粘弹壁板颤振分析

基于Kelvin粘弹模型,根据Von Karman大变形应变-位移关系和一阶活塞气动力理论,运用伽辽金方法建立了三维粘弹壁板颤振方程,并采用Rouge-Kutta法进行数值积分,分析粘弹阻尼,面内压力及壁板几何尺寸对粘弹壁板颤振的影响,进而取动压为分叉参数,研究粘弹壁板颤振时的分叉及混沌等特性。结果表明：随着粘弹性阻尼的增大, 系统的静态稳定区域先减小后增大,而静态屈曲解几乎不受影响,同时发现混沌运动区域随着粘弹阻尼的增大而快速减小。当取动压为分叉参数时发现粘弹壁板分叉特性很复杂,系统由屈曲状态进入混沌振动,再经历一系列的分叉进入简谐极限环振动状态;而较大面内压力和较小的长宽比不利于粘弹壁板的稳定。     

弹性支承对三维曲壁板颤振特性的影响

提出了一种在四边简支曲壁板上附加一个弹性支承来提高曲壁板颤振临界动压的方法,研究了弹性支承的位置和刚度对曲壁板颤振速度的影响规律。应用von Karman大变形应变-位移关系来描述曲壁板的结构大变形,用一阶活塞气动力理论计算曲壁板的气动力,采用虚功原理和有限元方法,建立起带弹性支承的圆柱壳曲壁板在超音速气流中的颤振方程。通过求解曲壁板系统的特征方程获得其颤振临界动压。运用频率重合理论分别分析了改变弹性支承刚度和位置对曲壁板颤振特性的影响。结果表明,与不带弹性支承的曲壁板颤振特性相比,弹性支承位于不同位置时,会对曲壁板的颤振动压产生明显不同的影响:1弹性支承位于曲壁板中心点附近区域或位于弦向中线上时,都会导致曲壁板颤振动压降低且随着支承刚度的增大而减小;在曲壁板中心点处,颤振动压降低幅度最大;2弹性支承位置沿垂直于气流方向且远离弦向中线变化时,都会使颤振动压提高,且随着支承刚度的增大而增大;3当支承位置在前缘和后缘部位顺气流方向变化时,颤振动压都会提高;4采用附加弹性支承的方法来提高曲壁板颤振动压时,应将弹性支承布置在曲壁板展向中线距边界20%弦长处。     

用Normal Form直接法研究壁板的热颤振与控制

建立了二维受热壁板在超音速气流中的颤振方程。运用分岔理论求得了系统的Hopf分岔点,应用Normal Form直接法计算得到系统Hopf分岔Normal Form系数。引入wash-out滤波器技术对壁板热颤振进行了主动控制,延迟系统Hopf分岔的产生而不改变分岔类型。最后采用数值模拟验证了理论分析。     

动力吸振器用于夹层壁板颤振抑制的研究

提出了用动力吸振器来抑制夹层壁板颤振的新方法,将壁板设计成芯层分布安装微型动力吸振器的夹层壁板,针对壁板第一阶共振模态进行吸振设计,计算和分析了夹层壁板、带刚性梁夹层壁板和带吸振器夹层壁板的振动特性、频率响应特性和颤振特性.结果显示,吸振器能大幅度提高壁板的颤振速度,抑制夹层壁板颤振发生.     

三维壁板热颤振分析

基于一阶活塞气动力理论,根据Von Karman大变形应变-位移关系并用伽辽金方法建立了三维壁板热环境下颤振方程,分析讨论两种温度分布及壁板几何尺寸对系统稳定性的影响.结果表明:随温度的升高,两种温度分布颤振临界动压都减小,系统的稳定性降低,但均匀温度分布颤振临界动压下降得要大,温度效应更加明显;壁板长宽比的增大有利于壁板的稳定.在两种温度分布及不同长宽比的参数下,壁板振动都呈现了五种形态::衰减振动、极限环振动、后屈曲振动、非简谐的周期性振动和混沌型振动.     

Thermal post-buckling and the stability boundaries of structurally damped functionally graded panels in supersonic airflows

In this study, the thermal post-buckling behaviors and linear flutter analysis of structurally damped functionally graded (FG) panels under a supersonic airflow are investigated. The material properties are assumed to be temperature-dependent and vary in the thickness direction of the panel. First-order shear-deformation theory (FSDT) is applied to model the panel, and the von Karman strain–displacement relations are adopted to consider the geometric nonlinearity. In addition, the damping is modeled as the Rayleigh damping, and first-order piston theory is applied for the supersonic aerodynamic load. Results are obtained for the thermal post-buckling behavior, and linear flutter analysis of FG panels with a damping effect is performed to search for the origin of the flutter. The numerical data are validated through a comparison with the previous works, and the effects of structural damping are discussed in detail for various cases.     

Flutter analysis of cantilevered curved composite panels

A 48 degrees of freedom (dof) doubly curved quadrilateral thin shell finite element is used for studying the supersonic flutter of cantilevered curved composite panels. The composite material behavior is included using classical lamination theory and supersonic aerodynamic behavior is included using linearized piston theory. To reduce the number of dof of the finite element aeroelastic system, a normal mode approach is adopted. Results are presented to illustrate the behavior of flutter characteristics for composite curved cylindrical panels. The effects of fiber orientation and flow angle on the flutter characteristics are presented for selected examples. The accuracy, efficiency, and applicability of the present finite element method is demonstrated by illustrative examples with some results comparing well with the available alternate solutions in the literature.     

Free vibration and flutter of damaged composite panels

A finite element method is investigated for studying the free vibration and supersonic flutter analysis of arbitrary damaged composite panels. The finite element method employs a 48 degrees of freedom (DOF) general plate element and uses the classical lamination theory, microstructural continuum damage theory and linearized piston theory. Two different damage models were investigated. Finite element results are obtained to illustrate the effect of damage on the eigenvalues and flutter boundaries. The results obtained indicate that between the two models considered, damage model 1 has a strong influence on both free vibration and flutter boundaries.     

A parametric study on supersonic/hypersonic flutter behavior of aero-thermo-elastic geometrically imperfect curved skin panel

In this paper, the effect of the system parameters on the flutter of a curved skin panel forced by a supersonic/hypersonic unsteady flow is numerically investigated. The aeroelastic model investigated includes the third-order piston theory aerodynamics for modeling the flow-induced forces and the Von Kármán non-linear strain-displacement relation in conjunction with the Kirchhoff plate hypothesis for the panel structural modeling. Structural non-linearities are considered and are due to the non-linear coupling between out-of-plane bending and in-plane stretching. The effects of thermal degradation and Kelvin??s model of structural damping independent on time and temperature are also considered. The aero-thermo-elastic governing equations are developed from the geometrically imperfect non-linear theory of infinitely long two-dimensional curved panels. Computational analysis and discussion of the finding along with pertinent conclusions are presented.     

Active aeroelastic flutter analysis and vibration control of supersonic composite laminated plate

The active aeroelastic flutter analysis and vibration control at the flutter bounds of the supersonic composite laminated plates with the piezoelectric patches are studied. The piezoelectric patches are bonded on the top and bottom surfaces of the composite laminated plate to act as the sensor and actuator so that the active aeroelastic flutter suppression and vibration control for the supersonic laminated plate can be conducted. The unsteady aerodynamic pressure in supersonic flow is computed by using the supersonic piston theory. Hamilton’s principle with the assumed mode method is used to develop the governing equation of the structural system. The controller is designed by the velocity feedback and proportional feedback control algorithm, and the active damping and stiffness are obtained. The solutions for the complex eigenvalue problem are obtained by using the generalized eigenvalue methodology. The natural frequencies and damping ratios are also gotten. The aeroelastic flutter bounds of the supersonic composite laminated plate are calculated to investigate the characteristics of the aeroelastic flutter. The impulse responses of the structural system are calculated by using the Houbolt numerical algorithm to study the active aeroelastic vibration control. The influences of ply angle of the laminated plate and the control method on the characteristic of flutter and active vibration control are analyzed. From the numerical results it is observed that the aeroelastic flutter characteristics of the supersonic composite laminated plate can be improved and that the aeroelastic vibration response amplitudes can be reduced, especially at the flutter points, by the proportional feedback or the velocity feedback control algorithm using the piezoelectric actuator/sensor pairs. The effectiveness of the flutter control by the two control algorithms is also compared. The results of this study are of great significance to the flutter analysis and aeroelastic design of the aircraft.     

采用等效刚度有限元模型的复合材料机翼颤振分析

采用等效刚度方法,研究了一种适用于机翼初步设计阶段的动力学和颤振分析的结构有限元模型。该方法首先计算不同布局形式的加筋壁板的刚度矩阵,然后将其赋予与加筋壁板平面形状相同的光板（等效板）上,使加筋壁板和等效板具相同的力学性能。该方法的优点是避免了加强筋的有限元建模,从而使有限元模型的复杂程度大大降低,但同时等效刚度结构有限元模型仍能反映机翼加筋壁板的结构特性。以某客机概念方案的机翼为例,建立了反映实际结构详细有限元及其等效刚度有限元模型。计算结果和对比分析表明,两种模型的固有频率、振动模态和颤振分析结果吻合得很好,从而验证了等效刚度方法在机翼结构动力学和颤振分析方面的准确性。由于该方法具有简单快速和准确的优点,可用于机翼初步设计阶段对颤振特性的评估。     

大攻角翼面颤振的一种改进的工程算法

提出一种以当地流活塞理论和当地流小扰动线化理论分别计算大攻角翼面激波脱体流态的局部超音速区和局部亚音速区的非定常气动力，以时域积分方法求解颤振方程。改进大攻角翼面颤振分析的工程计算方法，并与风洞颤振试验结果进行了对比，计算精度满足工程设计要求。     

Active aeroelastic flutter suppression of a supersonic plate with piezoelectric material

The active aeroelastic flutter properties of supersonic plates are investigated by using the piezoelectric material. The piezoelectric material has been extensively used for the active vibration control of engineering structures. In this paper, the piezoelectric material is further used to improve the flutter characteristics of the supersonic plates. The equation of motion of the plate and piezoelectric material system is obtained by Hamilton’s principle with the assumed mode method. The supersonic piston theory is used to evaluate the aerodynamic load. By applying an appropriate external control voltage to activate the piezoelectric material, a displacement and acceleration feedback control strategy is used to obtain the active stiffness and active mass. Solving the eigenvalue problem of the equation of motion, the natural frequencies and damping ratios of the structural system are obtained. Furthermore, the aeroelastic flutter bounds are calculated, and the effects of feedback control gains on the active aeroelastic flutter characteristics of the structure are analyzed in detail. From the numerical results it is seen that the active stiffness and active mass have prominent effects on the flutter characteristics of the supersonic plates. The aeroelastic flutter properties can be greatly improved by introducing the active stiffness and active mass into the supersonic plate with the piezoelectric patch. With the increase of the feedback control gains, the active aeroelastic flutter properties for the lower order modes of the supersonic plate are gradually improved.     

Supersonic flutter prediction of functionally graded cylindrical shells

The supersonic flutter analysis of simply supported FG cylindrical shell for different sets of in-plane boundary conditions is performed. The aeroelastic equations of motion are constructed using Love’s shell theory and von Karman–Donnell-type of kinematic nonlinearity coupled with linearized first-order potential (piston) theory. The material properties are assumed to be temperature-dependant and graded across the thickness of the shell according to a simple power law. The temperature distribution is assumed to vary in the thickness direction and is obtained by solving the steady-state heat conduction equation. The pre-stresses due to the thermal and mechanical loadings are obtained by exact solution of the equilibrium equations. The Galerkin method is used to solve the aeroelastic equations of motion employing appropriate displacement functions. The effects of internal pressure and temperature rise on the flutter boundaries of the simply supported FG cylinder with different values of power-law index are investigated.