一类梁系结构线性稳定性分析的简化处理

本文给出了旋转壳与支承支柱系统组合结构线性稳定性分析的简化处理方案，即将空间梁系结构每根梁的单元刚度了四及几何阵按离散富氏系数变量叠加得等效刚度阵及几何阵。从所给算例智 ，这一简化处理是成功的，也说明稳定性分析反映的是结构的总体效应，局部区域的简化处理对整体结构临界载荷影响不大，但可使计算量大大减少。本文的计算方案及程序已应用于实际的冷却塔设计。     

拟协调等腰梯形壳元显式几何刚度阵及屈曲分析

采用拟协调元方法推导了等腰梯形薄壳元的显式几何刚度阵，用于组合结构屈曲分析的计算，结果表明，这种单元的几何刚度阵收敛快、精度好。     

拟协调等梯形壳元显式几何刚度阵及屈曲分析

采用拟协调元方法推导了等腰梯形薄壳元的显式几何刚度阵，用于组合结构屈曲分析的计算，结果表明，这种单元的几何刚度阵收敛快、精度好。     

四节点二十四自由度平板壳单元几何刚度矩阵显式解析式的推演算法研究

几何刚度矩阵的推演是结构几何非线性有限元分析的重点和难点之一。推导几何刚度矩阵显式解析表达式成为简化非线性有限元列式,提高分析效率的关键。本文在协同转动法框架下,基于刚体运动法则对四节点二十四自由度的平板壳单元几何刚度矩阵显式解析式进行了推导和讨论;分析了悬臂梁大转动、不同壁厚条件下简支圆柱形屋顶空间大变位两个经典算例。研究结果表明：（1）几何刚度矩阵的显式计算公式不仅为板壳结构几何非线性列式提供了方便而且具有良好的精度;（2）推导的几何刚度矩阵适用于各类型四边形二十四自由度平板壳单元模型;（3）与数值积分相比,采用解析形式的几何刚度矩阵可以显著提高非线性响应计算效率。     

静电陀螺监控器

本文介绍一种简化几何式惯性导航系统的静电陀螺监控器方案,这种简化几何式系统实质上是自由方位水平座标系和惯性座标系的组合。它和几何式惯性导航系统的主要差别是用静电陀螺取代经度和纬度陀螺,因此不能用几何关系直接测出载体经度,但可用计算方法求出。可用几何关系直接测出纬度,也可用计算方法同时求出经、纬度和航向。这种系统的主要优点是简化了结构,放宽了对静电陀螺仪体积的限制,而且系统的自对准和自校准也简便易行,并可实行全球航行。     

蜂窝芯层的等效弹性参数

反映蜂窝材料等效弹性参数的Gibson公式结果简单，便于应用然而由于对应于蜂窝壁板伸缩变形的刚度被忽略，导致蜂窝夹层结构数值分析时，芯层材料的弹性矩阵表现出不确定性本文重新考虑了蜂窝壁板的伸缩变形对面内刚度的影响，对Gibson公式进行了修正本本文结果不但克服了Gibson公式的缺陷，同时提出了考虑蜂窝芯层面内刚度的一种简化方案,该方案可以方便地应用于蜂窝夹层结构的计算。     

部分对称结构的分析理论

本文把群论方法与子结构分析的概念结合在一起,处理部分对称结构的分析问题,对于不可约基矢上的广义位移,文中指出了任何一个对称子结构模式的内部阵的三角化以及出口阵的凝聚都可以分成一系列子问题单独地进行。文中还给出了从各子问题的凝聚出口阵回到原位移基底上的凝聚出口阵的一种简化后的转换关系,从而使计算工作量又得到进一步缩减。 与普通的重复子结构方法相比,本文给出的方法在计算速度上有大幅度地提高。     

等几何壳体分析与形状优化

首先基于Reissner-Mindlin理论进行了三维壳体等几何分析,而后基于此对三维壳体进行形状优化,提出了形状优化中灵敏度的全解析计算方法,包括位移应变阵、雅克比阵和刚度阵等相对控制顶点位置的灵敏度解析计算公式;通过实例验证了壳体等几何分析和灵敏度全解析计算方法的有效性。与传统的基于网格的灵敏度半解析计算方法相比,基于NURBS的灵敏度全解析计算具有精确、计算效率高的特点,且可以避免优化迭代中的网格畸变。     

等几何壳体分析与形状优化

首先基于Reissner-Mindlin理论进行了三维壳体等几何分析,而后基于此对三维壳体进行形状优化,提出了形状优化中灵敏度的全解析计算方法,包括位移应变阵、雅克比阵和刚度阵等相对控制顶点位置的灵敏度解析计算公式;通过实例验证了壳体等几何分析和灵敏度全解析计算方法的有效性。与传统的基于网格的灵敏度半解析计算方法相比,基于NURBS的灵敏度全解析计算具有精确、计算效率高的特点,且可以避免优化迭代中的网格畸变。     

列车轮对简化模型重力刚度与滚动半径的计算方法

在建立列车轮对简化模型动力学方程中,如果假设侧移和摇头角是微小量,及质心高度保持不变,可以较简便地求出重力刚度和滚动半径等量的近似表达式。本文用几何方法给出了轮对质心高度和滚动半径与侧向位移之间的函数关系,从而可以获得这些量的解析表达式;另外还通过运动学方法,证明了重力刚度和滚动半径等量的简便计算方法是正确的。     

自然通风冷却塔的实验及有限元分析

本文以宁海电厂二期冷却塔为例简要介绍了冷却塔进行刚性模型及气弹模型试验的情况,用通用有限元软件ANSYS及专用冷却塔抗震分析软件LBSD进行冷却塔内力分析、稳定性分析、抗震分析,用刚性模型试验结果计算风振系数,并将计算结果与气弹模型试验的结果进行比较,所得结果对相关冷却塔设计与安全评估有重要工程意义.     

Buckling of cooling tower shells with ring-stiffeners

With the stability analysis of hyperbolic cooling tower shells with ring-stiffeners, our paper proposes the linear pre-buckling consistent theory. The numerical result shows that this linear analysis method is very effective and practical in engineering, for its precision of computation is up to the level of the nonlinear analysis when it is used for the study of critical loads of the hyperbolic cooling tower which is mainly governed by wind pressure and for the study of the effect of some other factors concerned in design on the buckling of shells. Based on that, we have obtained a series of conclusions which will greatly benefits the engineering design when discussing the effect on the critical wind loading of the shell which is caused by the following factors such as the position of rings, the number of rings and the dead weight.     

Nonlinear dynamic stability analysis of Euler–Bernoulli beam–columns with damping effects under thermal environment

In this study, a unified nonlinear dynamic buckling analysis for Euler–Bernoulli beam–columns subjected to constant loading rates is proposed with the incorporation of mercurial damping effects under thermal environment. Two generalized methods are developed which are competent to incorporate various beam geometries, material properties, boundary conditions, compression rates, and especially, the damping and thermal effects. The Galerkin–Force method is developed by implementing Galerkin method into force equilibrium equations. Then for solving differential equations, different buckled shape functions were introduced into force equilibrium equations in nonlinear dynamic buckling analysis. On the other hand, regarding the developed energy method, the governing partial differential equation for dynamic buckling of beams is also derived by meticulously implementing Hamilton’s principles into Lagrange’s equations. Consequently, the dynamic buckling analysis with damping effects under thermal environment can be adequately formulated as ordinary differential equations. The validity and accuracy of the results obtained by the two proposed methods are rigorously verified by the finite element method. Furthermore, comprehensive investigations on the structural dynamic buckling behavior in the presence of damping effects under thermal environment are conducted.     

Buckling analysis of two layer delaminated beams with bridging

Stitching has been used as through-thickness reinforcement to reduce the effects of delamination. In stitching, the delamination will be held by stitches in the form of crack/interface bridging. In the present work, the reinforcement of stitching threads is assumed to provide continuous linear restoring tractions opposing the delamination opening. A generalized mathematical model is developed to study the buckling analysis of two layer delaminated beams with bridging by using Rayleigh–Ritz energy method. The delaminated beam is analyzed as four interconnected beams using the delamination as their boundary. Lagrange multipliers are used to enforce the boundary and continuity conditions between the junctions of the interconnected beams. The developed mathematical model is solved as an eigenvalue problem in which the lowest eigenvalue gives the buckling load. Effective-bridging modulus, a new nondimensionalized parameter, is introduced to study the influence of bridging on the delamination buckling. It is shown that bridging strongly influences the buckling load of the delaminated beams and a monotonic relation is observed between the buckling load and the effective-bridging modulus. Parametric studies in terms of delamination sizes and locations along spanwise and thicknesswise positions on the buckling load have been carried out. The bridging is found to be effective for shallow delaminations of moderate length, and for deep and long delaminations. Spanwise positions of delamination strongly influence the buckling loads. In addition, an analytical model for obtaining upper bounds of the buckling load is developed by using Euler–Bernoulli beam theory. Effective-slenderness ratio, a new nondimensionalized parameter is defined and it is found to be controlling the buckling mode configurations, i.e., local, global and mixed modes.     

A Motion Amplifier Using an Axially Driven Buckling Beam: I. Design and Experiments

For active materials such as piezoelectric stacks, which produce large force and small displacement, motion amplification mechanisms are often necessary – not simply to trade force for displacement, but to increase the output work transferred through a compliant structure. Here, a new concept for obtaining large rotations from small linear displacements produced by a piezoelectric stack is proposed and analyzed. The concept uses elastic (buckling) and dynamic instabilities of an axially driven buckling beam. The optimal design of the buckling beam end conditions was determined from a static analysis of the system using Euler's elastica theory. This analysis was verified experimentally. A stack-driven, buckling beam prototype actuator consisting of a pre-compressed PZT stack (140 mm long, 10 mm diameter) and a thin steel beam (60 mm× 12 mm× 0.508 mm) was constructed. The buckling beam served as the motion amplifier, while the PZT stack provided the actuation. The experimental setup, measuring instrumentation and method, the beam pre-loading condition, and the excitation are fully described in the paper. Frequency responses of the system for three pre-loading levels and three stack driving amplitudes were obtained. A maximum 16^∘ peak-to-peak rotation was measured when the stack was driven at an amplitude of 325 V and frequency of 39 Hz. The effects of beam pre-load were also studied.     

大型冷却塔结构分析的若干问题

简要介绍大型自然通风冷却塔结构设计中所遇到的问题,以及冷却塔的应力分析、抗震分析、稳定性分析和风振等研究的进展.     

基于立体打印自然通风冷却塔模型稳定性试验研究

为研究自然通风冷却塔在风载荷下的屈曲模式及临界风速,用立体打印技术打印了三个不同壁厚的缩尺模型,在风洞中完成了稳定性试验,并将实验结果与有限元计算结果进行对比分析.研究表明,模型失稳发生在弹性阶段,其壁厚与喉部半径之比是确定临界载荷的一个关键参数.实验得到的临界风压值同现有规范的设计相接近,约为有限元计算的1/4,说明我国现有规范中基于冷却塔整体稳定性得到的最小壁厚是偏保守的.     

Hamilton体系下功能梯度梁的热冲击动力屈曲分析

在Hamilton体系下,基于Euler梁理论研究了功能梯度材料梁受热冲击载荷作用时的动力屈曲问题;将非均匀功能梯度复合材料的物性参数假设为厚度坐标的幂函数形式,采用Laplace变换法和幂级数法解析求得热冲击下功能梯度梁内的动态温度场:首先将功能梯度梁的屈曲问题归结为辛空间中系统的零本征值问题,梁的屈曲载荷与屈曲模态分别对应于Hamilton体系下的辛本征值和本征解问题,由分叉条件求得屈曲模态和屈曲热轴力,根据屈曲热轴力求解临界屈曲升温载荷。给出了热冲击载荷作用下一类非均匀梯度材料梁屈曲特性的辛方法研究过程,讨论了材料的梯度特性、结构几何参数和热冲击载荷参数对临界温度的影响。     

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress–strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.     

框架结构屈曲的精确有限元求解

基于屈曲微分控制方程的一般解,构造了Euler梁在轴力作用下的精确形函数,建立了用于框架结构屈曲分析的精确有限单元,得到了单元刚度矩阵和几何刚度矩阵的显式表达,并提出了基于常规特征值计算的迭代算法以确定屈曲载荷及相应失稳模态的精确解. 研究表明, 对于线性稳定性分析而言,常规框架有限单元可视为精确有限单元的一种近似. 若采用精确单元,无需进行网格细分就可以获得精确的屈曲载荷和失稳模态. 数值算例证明了新单元和算法的效率和精度.