基于径向基函数的网格变形及非线性气动弹性时域仿真研究

为开展非线性气动弹性研究,基于非线性结构有限元软件NASTRAN和自主研制的多块结构化计算流体力学(CFD)求解器,开发了一套基于计算流体力学/计算结构动力学(CFD/CSD)耦合求解方法的气动弹性时域仿真程序.该程序采用径向基函数(RBF)交换两套求解器之间的数据并进行网格变形.为提高RBF方法的效率,构造了基于多次插值的空间待插值点精简算法.在多次插值过程中,每次插值的对象为上次插值的误差,并同时限制插值区域,以此实现了空间待插值网格数的精简.数个网格变形的算例表明该方法可支持大变形运动,并且具有较高的计算效率.采用此程序开展了AGARD 445.6机翼颤振计算、大展弦比机翼的静气动弹性计算与切尖三角翼极限环振荡(LCO)现象的动气动弹性仿真,结果揭示了当机翼展弦比较大或者响应幅值较大时,结构非线性对于气动弹性有显著影响.     

Static aeroelastic analysis of very flexible wings based on non-planar vortex lattice method

A rapid and efficient method for static aeroelastic analysis of a flexible slender wing when considering the structural geometric nonlinearity has been developed in this paper. A non-planar vortex lattice method herein is used to compute the non-planar aerodynamics of flexible wings with large deformation. The finite element method is introduced for structural nonlinear statics analysis. The surface spline method is used for structure/aerodynamics coupling. The static aeroelastic characteristics of the wind tunnel model of a flexible wing are studied by the nonlinear method presented, and the nonlinear method is also evaluated by comparing the results with those obtained from two other methods and the wind tunnel test. The results indicate that the traditional linear method of static aeroelastic analysis is not applicable for cases with large deformation because it produces results that are not realistic. However, the nonlinear methodology, which involves combining the structure finite element method with the non-planar vortex lattice method, could be used to solve the aeroelastic deformation with considerable accuracy, which is in fair agreement with the test results. Moreover, the nonlinear finite element method could consider complex structures. The non-planar vortex lattice method has advantages in both the computational accuracy and efficiency. Consequently, the nonlinear method presented is suitable for the rapid and efficient analysis requirements of engineering practice. It could be used in the preliminary stage and also in the detailed stage of aircraft design.     

间隙约束二元翼段系统分岔与多解共存现象分析

研究了分段刚度描述的间隙约束二元翼段气动弹性系统,取俯仰角最大幅值处为类Poincaré截面,数值计算得到了系统随飞行速度变化的分岔图,发现飞行速度在Ma=0.71~0.75属于跨临界颤振区,而在Ma=0.75~0.95发生极限环震荡.同时通过构造极限环震荡的四维Poincaré映射分析了极限环震荡的稳定性,结合稳定性和运动流形理论,得到极限环震荡的吸引域一般位于极限环内部并用数值方法进行了验证.且跨临界颤振速度区域中存在多种分岔形式以及多解共存现象,例如由双周期运动直接通向混沌、多周期运动与双周期运动共存现象,振动幅值也存在跳跃现象.     

柔性飞机非线性气动弹性与飞行动力学耦合静、动态特性

高空长航时(HALE)飞机结构细长、具有柔性,在常规飞行条件下可发生结构大变形、气动失速以及结构低频振动与刚体运动耦合,这些现象显著影响其静、动态特性.基于几何精确完全本征运动梁模型、ONERA动失速气动力模型和六自由度刚体运动模型,建立了考虑几何非线性、动失速和材料各向异性等因素的大展弦比柔性飞机非线性气动弹性与飞行...     

速率限制舵机描述函数模型研究

基于电传飞行控制系统中速率限制舵机的非线性特征,建立了速率限制舵机的简化模型.提出运用描述函数法建立速率限制舵机的精确正弦描述函数模型、高度饱和与近饱和描述函数模型.将高度饱和与近饱和描述函数模型的频率特性与精确正弦描述函数模型的频率特性进行了对比研究,获得了高度饱和与近饱和描述函数模型的使用域.研究结果可为控制系统中...     

失谐叶盘结构振动问题研究新进展

失谐叶盘结构的研究对航空发动机振动设计和提高其可靠性、完整性具有重要的意义。本文全面阐述了国内外失谐叶盘结构研究的新进展,重点对近年来研究的热点问题：建模、局部化、失谐优化与灵敏度、非线性、失谐识别、多重耦合与颤振等做了详细的评述与讨论,综合了最新的研究方法和取得的成果,对一些新出现的重要研究方向,比如科氏力、多个部件耦合等问题进行了详细的总结,最后提出了需要进一步研究的问题。     

线化插值权残法求解强非线性振动问题

本文用线性化法，插值函数法和权残法相结合的方法求解了几类保守系统强非线性振动问题，其精度比已有的新的改进的L-P法还更好些。     

抑制飞控系统舵机间隙影响的非线性补偿器设计

通过对舵机间隙非线性特性的分析和极限环的定义及产生条件的讨论,在飞控系统中采用非线性补偿的方法,设计了间隙补偿器,并介绍了其工程实现方法,进行了相应的数字仿真和半物理仿真试验以及试验结果的对比分析。结果表明,此方法有效地解决了飞控系统由于舵机间隙引起的超调与极限环振荡现象,使飞控系统对舵机的频率特性以及间隙各方面要求大大降低,其工程实现方法简单实用、普遍性较强,具有较高的工程应用价值。     

基于三类非线性函数的认证码的构造

为了将高度非线性函数应用于认证码构造理论．讨论了非线性函数的度量，给出了由三类非线性函数构造的Cartesian认证码，并且当编码规则按等概率分布选取时，分别计算了三类认证码的模仿攻击和欺骗攻击成功的概率。结果表明，第二类认证码模仿攻击成功的概率达到了下界。在n取值相同的条件下，第一类认证方案模仿攻击成功的概率比第三类的大。     

Aeroservoelastic stability analysis for flexible aircraft based on a nonlinear coupled dynamic model

A unified theoretical aeroservoelastic stability analysis framework for flexible aircraft is established in this paper. This linearized state space model for stability analysis is based on nonlinear coupled dynamic equations, in which rigid and elastic motions of aircraft are both considered. The common body coordinate system is utilized as the reference frame in the deduction of dynamic equations, and significant deformations of flexible aircraft are also fully concerned without any excessive assumptions. Therefore, the obtained nonlinear coupled dynamic models can well reflect the special dynamic coupling mechanics of flexible aircraft. For aeroservoelastic stability analysis, the coupled dynamic equations are linearized around the nonlinear equilibrium state and together with a control system model to establish a state space model in the time domain. The methodology in this paper can be easily integrated into the industrial design process and complex structures. Numerical results for a complex flexible aircraft indicate the necessity to consider the nonlinear coupled dynamics and large deformation when dealing with aeroservoelastic stability for flexible aircraft.