新的复合材料格栅加筋板的平铺等效刚度法

针对薄壁复合材料格栅加筋结构的受力特点,在改进原有力学假设的基础之上,推导了一种新的平铺等效刚度计算方法,它充分考虑了筋条和面板之间的相互作用.通过格栅单元结构布局形式的参数化表示,建立了通用的力学分析模型;该模型可用于分析各种结构布局形式和面板铺层方式下的结构总体屈曲问题,故对于航空航天结构设计非常有用.结合Rayleigh-Ritz方法,推导出了求解格栅加筋板屈曲载荷的通用线性特征方程;最后,分析了多种类型格栅结构的算例,并与现有的各种方法进行了比较,结果更为精确,因而对格栅加筋结构的优化设计具有很好的应用价值.     

薄板结构加筋布局优化设计方法研究

提出一种两步优化策略,以加筋板结构的固有频率最大化为目标函数,以结构所受外载荷作用的最大静变形为约束条件,开展薄板结构加筋构件的布局优化设计研究。为了降低加筋布局优化的难度,提高优化设计的效率,将加筋等效为一系列弹性铰（点）支撑,以便快速获得加筋横向移动的灵敏度信息。在基本不改变结构重量的情形下,通过合理布局加筋位置,能显著改善结构的刚度分布,提高结构的整体承载能力。随后,小幅调整加筋的截面尺寸,以满足对结构最大变形的设计要求。最后,用两个算例验证了所提优化方法的可行性和有效性。     

剪切载荷下肋板的屈曲分析与优化

利用ANSYS有限元方法分析了一系列的肋板,研究了加强肋的作用,提出了优化肋设计的限制条件. 结果表明,由横向肋板产生的栅格数目不能小于肋板的长宽比. 换句话说,横向加强肋必须把平板的长度划分为小于等于宽度的段. 结果还显示,加强肋的优化几何特性与板的屈曲从整体模态到局部模态转变点相应. 而且,所有具有相似长宽比和肋数的肋板,具有一个特定的比值$EI_{s}/aD$, 此时抗剪应力最佳.     

固支加筋方板在爆炸载荷作用下的刚塑性动力响应分析

采用能量法分析了固支加筋方板在爆炸载荷作用下的刚塑性动力响应。提出了该类结构在这种载荷作用下的两种变形模态和模态判别条件，导出了计及膜力影响的最大残余横向变形的计算方法及计算公式。并对两种变形模态进行了试验研究，取得了理论计算值与试验值相一致的好结果。     

基于代理模型和等效刚度模型的加筋柱壳混合优化设计

针对轴压作用下的加筋柱壳后屈曲性能优化计算较大的问题,本文提出了一种基于代理模型和等效刚度模型的混合优化策略,即运用基于等效刚度的平铺模型进行有限元后屈曲分析以代替试验设计中大量的精细加筋模型分析,并通过控制等效模型的单元尺寸来调整其分析精度,而等效刚度模型计算时长仅约为精细加筋模型的1/3。对构建的代理模型采用多岛遗传算法进行极限承载力等约束下的轻量化设计,调用精细模型有限元后屈曲分析对代理模型进行更新,从而保证代理模型的拟合精度并得到优化解。工程算例结果表明,本文提出的混合优化方法,使加筋柱壳结构在满足承载力情况下减重效果明显。     

板状材料上加强筋的几何形状对兰姆波透射特性的影响

为研究板状材料上加强筋结构对兰姆波透射特性的影响,通过有限元仿真和实验的方法,结合兰姆波频散曲线和二维傅里叶变换分析方法,研究了不同几何形状的加强筋结构对兰姆波垂直入射时的透射特性。仿真与实验的结果表明:加强筋结构会对兰姆波产生梳状滤波器效应,即同一几何形状的加强筋对不同频率的兰姆波透射程度不同;梳状滤波器的通带带宽和通带个数受到加强筋几何形状的影响;随着加强筋高度的增加,梳状滤波器的通带带宽变小且通带个数增加;随着加强筋厚度的增加,梳状滤波器的通带带宽和个数并不呈现单调变化;对于同一高厚比的加强筋,随着加强筋体积的变大,梳状滤波器的通带宽变小且通带个数增加。该研究结果可用于指导利用兰姆波对具有加强筋结构的板状材料进行结构健康监测和无损检测时兰姆波有效频率的选择,从而提高兰姆波能量的利用率和信号的信噪比。     

Reinforcement of a thin plate by a thin layer

We study the bending of a thin plate, stiffened with a thin elastic layer, of thickness δ. We describe the complete construction of an asymptotic expansion with respect to δ of the solution of the Kirchhoff–Love model and give optimal estimates for the remainder. We identify approximate boundary conditions, which take into account the effect of the stiffener at various orders. Thanks to the tools of multi‐scale analysis, we give optimal estimates for the error between the approximate problems and the original one. We deal with a layer of constant stiffness, as well as with a stiffness in δ^?1. Copyright © 2007 John Wiley & Sons, Ltd.     

曲线加筋Kirchhoff-Mindlin板自由振动分析

相比传统加筋板,曲线加筋板能够更充分地发挥材料力学性能.在加筋板力学分析中,厚板通常采用Reissner-Mindlin理论,然而当板厚较薄时易出现剪切自锁,离散的Kirchhoff-Mindlin理论采用假设剪切应变场可避免该问题.针对曲线加筋Kirchhoff-Mindlin板自由振动分析,采用离散的Kirchhoff-Mindlin三角形单元和Timoshenko曲梁单元分别模拟板和加强筋,根据板的位移插值函数及筋板交界面的位移协调条件,建立基于板单元位移自由度的有限元方程.为了验证方法的有效性和准确性,采用直线加筋薄板、曲线加筋薄板和厚板3种模型进行算例研究,通过收敛性和精度分析来选择合理的有限元网格密度.直线加筋薄板前20阶固有频率均与文献结果吻合良好;曲线加筋板算例中,本文方法满足收敛条件的板单元数目为2469,Nastran模型板单元数目为6243;本文所得曲线加筋板固有频率与Nastran计算结果最大误差为3.4%.研究结果表明,本文方法无需筋板单元共节点,可使用较少的有限元网格数量,并能够保证计算精度;在离散Kirchhoff-Mindlin三角形板单元基础上构造Timoshenko梁单元可同时适用于曲线加筋薄板与厚板自由振动分析.     

Thermal buckling and free vibration of FG truncated conical shells with stringer and ring stiffeners using differential quadrature method

In this paper, thermal buckling and free vibration of orthogonally stiffened functionally graded truncated conical shells in thermal environment is investigated. Conical shell has been stiffened by rings and stringers, and the influences of the stiffeners are evaluated by the aid of smearing method. The material properties of the structure are assumed to be changed continuously in the thickness direction. First, the initial thermal stresses are obtained accurately by solving the thermoelastic equilibrium equations. Then, by taking into account the initial thermal stresses, equations of motion as well as boundary conditions are obtained, applying the Hamilton’s principle and the first-order shear deformation theory. The natural frequencies of the system have been achieved, solving these governing equations with considering Differential Quadrature Method (DQM). In addition to Eigen frequency analysis, the critical buckling-temperature of the conical shell has been computed. Moreover, the effects of geometrical parameters, number of stiffeners, thermal environment and various boundary conditions on natural frequency of the system have been investigated. Finally, in order to validate the present work, the results are compared with those of other researches available in literature.     

Deployable lenticular stiffeners for origami-inspired mechanisms

Light-weight origami-inspired mechanisms can provide advantages in deployable space systems and other applications. However, a significant challenge in their design is ensuring that they are su?ciently stiff. Compliant, deployable stiffeners utilizing a profile that approximates the Euler Spiral are proposed as one possible solution. It is shown that a structure with this specific profile, called a lenticular stiffener, permits stiffeners to be flattened using a force applied at their edge. Formulas for calculating the increase in stiffness are developed. Relations needed to design the deployment behavior of the stiffeners are also derived. Finally, advantages of different configurations of stiffeners are evaluated. These results are verified through simulation and experiments.