含初缺陷复合材料圆柱曲板的动力屈曲分析

基于修正的一阶剪切变形理论，利用Ｈａｍｉｌｔｏｎ原理导出包含横向剪切变形和转动惯量的复合材料长圆柱曲板的非线性动力方程，通过将位移和载荷展开为Ｆｏｕｒｉｅｒ级数，把非线性偏微分方程组转化为二阶常微分方程组，并可由四阶Ｒｕｎｇｅ－Ｋｕｔｔａ方法数值求解，通过算例，讨论了有关因素对迭层复合材料圆柱曲板动力屈曲的影响。     

板壳非线性问题的曲壳有限单元法

本文基于总体Lagrange坐标描述法,采用Kirchhoff应力张量定义和Green应变张量定义,导出了分析板壳非线性问题的曲壳有限单元法。通过引入新的单元几何非线性关系,本文方法可用于分析板壳的大挠度大转角情况。由于采用了材料本构关系的修正子增量形式,提高了有限单元的分析计算精度。本文采用增量—拟牛顿—子增量迭代技术求解板壳的荷载一位移曲线,与传统迭代方法相比大大提高了计算效率。此外,对于板壳任意边界条件的形成和任意初始形状的考虑问题,本文分别导出了罚单元法和局部坐标转换法予以处理。经计算比较,证明本文方法可以有效地用于板壳的弯曲、屈曲及屈曲后性态和极限强度等问题的非线性分析。     

轻质金属泡沫夹芯曲板的抗爆炸冲击响应研究

夹芯结构具有高比强度、高比刚度和优异的吸能能力,已经被广泛应用于工程结构用来抵御高强度的爆炸冲击载荷。本文采用有限元数值模拟方法研究了爆炸载荷作用下四边固支夹芯曲板的动力响应。比较了同等质量下夹芯曲板、夹芯平板、实体曲板和实体平板四种结构的抗爆炸冲击性能,讨论了不同曲率和非对称因子对结构动力响应的影响,得到了使得夹芯曲板抗爆炸性能最佳的非对称因子。研究结果表明：夹芯曲板的抗爆炸冲击性能优于等质量的夹芯平板、实体曲板和实体平板结构,增大夹芯曲板的曲率能够提高结构的抗爆炸冲击性能。     

圆柱坐标系中弹性力学的哈密顿正则方程及其哈密顿单元方法

给出圆柱坐标系中弹性力学的哈密顿形式体系，用有限元法得到了哈密顿单元的半解析解，可用于求解复合材料叠层圆柱曲板问题。     

圆柱形曲板的内压实验

文献[1]进行了圆柱形曲板在侧压作用下的应力分析计算.我们相应地做了圆柱形曲板的内压实验.实验装置、试件和边界条件的实现整个实验装置见图1.以压缩空气通过试件下部的橡皮囊进行加载,气压由 U 型水银压力计读出.为了实现曲板四边拉住简支的边界条件,我们设计了一套专用的夹具.     

加筋壁板轴压载荷下后屈曲稳定性试验研究

对11种构型的民用飞机机身加筋曲板在轴压载荷下后屈曲承载能力进行了试验和工程算法研究,深入探索了机身壁板的各种破坏模式,对极限法、Johnson）物线法与欧拉法三种工程算法比较,并且把试验结果与计算结果进行了对比。研究结果表明：壁板后屈曲轴压许用值与桁条剖面积和蒙皮厚度成线形关系,主要取决于桁条剖面积;蒙皮的局部屈曲应力对初始缺陷敏感,但局部屈曲应力的偏差对壁板的轴压破坏载荷影响不明显;与工程计算结果对比发现Johnson抛物线法计算的破坏轴压与试验结果吻合较好。     

基于不同板理论的嵌于柔性层中薄膜的皱曲分析

论文对于柔性层-薄膜-柔性层三层结构系统,基于经典板理论、一阶剪切变形理论和高阶剪切变形理论,分别推导给出薄膜皱曲的控制方程.对于两个柔性层,则把它们处理成具有有限厚度的平面应变弹性体.针对上下柔性层固支边界或自由边界条件,利用线性扰动方法得到柔性层对薄膜的横向压力差,最终获得确定薄膜具有周期性正弦型皱曲的临界载荷方程...     

非均匀性对材料分叉的作用

利用数值方法研究材料空洞化和承受应力沿板厚分布的非均匀性对材料分叉（平板中平面剪切带和表面皱曲）的作用。     

在均匀横向载荷作用下蜂窝夹层园柱曲板蜂格剪切失稳的实验

蜂窝夹层结构是一种比较好的结构型式。蜂窝园柱曲板在均匀横向载荷作用下,承载能力的问题是飞机设计中常会遇到的实际问题。本报告通过实验,观察了四边滑动简支蜂窝曲板丧失承载能力的现象和过程,又从理论上计算了蜂窝曲板在均匀横向载荷作用下,靠近边界的蜂格壁板剪切失稳的临界载荷,并与实验测得的试件丧失承载能力时的最大载荷(简称流动载荷)进行了比较。结果表明:后者比前者大4倍左右。      

夹层梁总体屈曲及皱曲的有限元计算

皱曲是夹层结构的一种短波屈曲模式,通常发生于夹心较厚或夹心刚度较低的情况。由于模型规模的限制,在常规有限元建模时通常将夹层板模拟为二维板单元,这种方法忽略了面板和夹心在厚度方向上的相互作用,无法计算出皱曲模式。针对上述问题,本文首先介绍了一个计算夹层结构总体屈曲和皱曲的统一理论,并将此理论的计算结果作为理论解。为了同时...     

A calculation method for fully developed flows in curved rectangular tubes

I.IntroductionacestudyofviscousnowincurvedtubesisoffundamentalinterestinfluidmechanicssincetheDean'spioneerwork(1928)l']oncurvedpipes.Therearenumerousapplications,whichincludetheflowsthroughturbomachinery,aircraftintakes,diffusersandheatexchangersetc.Itwa…     

HOPF BIFURCATION OF A NONLINEAR RESTRAINED CURVED PIPE CONVEYING FLUID BY DIFFERENTIAL QUADRATURE METHOD

This paper proposes a new method for investigating the Hopf bifurcation of a curved pipe conveying fluid with nonlinear spring support. The nonlinear equation of motion is derived by forces equilibrium on microelement of the system under consideration. The spatial coordinate of the system is discretized by the differential quadrature method and then the dynamic equation is solved by the Newton-Raphson method. The numerical solutions show that the inner fluid velocity of the Hopf bifurcation point of the curved pipe varies with different values of the parameter,nonlinear spring stiffness. Based on this, the cycle and divergent motions are both found to exist at specific fluid flow velocities with a given value of the nonlinear spring stiffness. The results are useful for further study of the nonlinear dynamic mechanism of the curved fluid conveying pipe.     

CHAOTIC TRANSIENTS IN A CURVED FLUID CONVEYING TUBE

I. INTRODUCTIONChaotic motion is a kind of reciprocal non-periodic motion caused by a deterministic system. Itis very sensitive to the initial conditions, apparently random and incapable of long-term prediction.Chaotic transient is such a motion that the system will undergo a final steady state, which is one ofseveral or much more possible steady motions of the system. But this final steady state is very sensitiveto the initial conditions of the system. As it is e?ected by many uncertain…     

一个新的八节点非协调曲边四边形平面单元

本文在文[1]和文[2]的基础上,提出构造非协调有限元的新方法。该方法不用一般的变分原理,可适用任意变系数正定和非正定偏微分方程。利用这一方法得到一个新的八节点四边形平面应力单元。与一般有限元相比,位移和应力可提高一阶收敛精度。形成单刚矩阵时,不需要进行数值积分。单元之间的协调条件容易满足,文中给出收敛性证明。文末给出数值算例,表明利用本文的方法,应力和位移均可获得满意的数值精度。     

曲线裂纹和反平面圆形夹杂相交问题

建立了和反平面圆夹杂界面相交的曲线裂纹的弱奇异积分方程,利用Cauchy型奇异积分方程主部分析方法研究了穿过反平面圆夹杂界面的曲线裂纹在交点处的奇性应力指数以及交点处角形域内的奇性应力,并根据奇性应力定义了交点处的应力强度因子。通过对弱奇异积分方程的数值求解,可得裂纹端点和交点处的应力强度因子。     

穿过反平面圆形夹杂界面的曲线型刚性线

利用复变函数方法和叠加原理建立了求解刚性线夹杂问题的弱奇积分方程,利用Ｃａｕｃｈｙ型奇异积分方程主部分方法,研究了穿过反平面圆夹杂界面的曲线型刚性线夹杂在界面交点处点处的奇性应力指数以及交点处角形域内的奇性应力,并定义了交点处的应力奇性因子。利用所得的奇性应力指数,通过对弱奇异积分方程的数值求解,得出了刚性线端点和交点处的应力奇性因子。     

ANTIPLANE CIRCULAR INCLUSION WITH A CURVED CRACK CROSSING THE BOUNDARY

The weakly singular integral equation used to solve the problem of the curved crack crossing the boundary of the antiplane circular inclusion is presented. Using the principal part analysis method of the Cauchy type integral equation, the singular stress index at the intersection and the singular stress of angular regions near the intersection are obtained. By using the singular stress obtained, the stress intensity factor at the intersection is, defined. After the numerical solution of the integral equation, the stress intensity factors at the end points of the crack and intersection are obtainable. The research is supported by National Natural Science Foundation of China (No. 59879012) and is the project of Chinese Foundation of State Education Commission (No. 98024832).     

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研制和开发了曲梁以及复合曲梁测量应力的创新实验装置, 通过该实验的设计、开发和应用,可以验证它的创新性和综合性,找出曲梁、复合曲梁与直 梁的诸多不同之处. 把该实验用于测试由钢制成的、钢与铜两种材料制成的,具有直角梯形 截面的简支梁在拱顶处受垂直集中力作用时的正应力和切应力,计算结果表明,理论解和实 验值吻合得很好.     

A study of properties of adaptive quadratic grids for three-dimensional near-surface field computations

Curved geometries and the corresponding near-surface fields typically require a large number of linear computational elements. High-order numerical solvers have been primarily used with low-order meshes. There is a need for curved, high-order computational elements. Typical near-surface meshes consist of hexahedral and/or prismatic elements. The present work studies the employment of quadratic meshes that are relatively coarse for field simulations. Directionally quadratic high-order elements are proposed for the near-surface field regions. The quadratic meshes are compared with the conventional low-order ones in terms of accuracy and efficiency. The cases considered include closed surface volume calculations, as well as computation of gradients of several analytic fields. A special method of adaptive local quadratic meshes is proposed and evaluated. Truncation error analysis for quadratic grids yields comparison with the conventional linear hexahedral/prismatic meshes, which are subject to typical distortions such as stretching, skewness, and torsion.     

基于Novozhilov理论带隔板连续弯箱位移参数的动态Bayes估计

推导了基于Novozhilov理论的简支弯箱有限曲条控制方程,并结合柔度法解决了带隔板连续弯箱的求解问题。首次建立了带隔板连续弯箱位移参数的动态Bayes误差函数,推导了相应的动态Bayes均值和方差表达式,提出步长的一维自动寻优方案后,结合共轭梯度法研究了带隔板连续弯箱位移参数的动态Bayes估计方法,同时给出了带隔板连续弯箱位移参数具体估计步骤。通过典型算例分析,总结了带隔板连续弯箱位移参数先验信息准确性判定方法及位移参数动态Bayes随机估计的其它重要结论。