双曲扁壳类汽车覆盖件刚度的试验研究

为进一步掌握汽车覆盖件刚度控制机制,建立了以双曲扁壳件为研究模型的成形试验及刚度测试分析系统.分别完成了成形工艺条件中不同压边力、拉深深度条件下,双曲扁壳件的成形试验,5种约束方式下的双曲扁壳件刚度测试试验.分析了压边力、拉深深度和约束方式对刚度的影响规律.研究表明:刚度测试时的约束方式对刚度有重要影响,约束越大,刚度越大;约束的改变对刚度的影响远大于其他工艺条件(压边力和拉深深度)对刚度的影响,提出刚度测试时为准确获得成形工艺条件等对刚度影响的最佳约束方式;工艺条件中压边力及拉深深度的变化对刚度亦有不同程度的影响,刚度随着压边力的增加而增大;成形时的拉深深度越大,刚度值也越大.上述工艺条件的改变对刚度的影响远大于厚度减薄对刚度的影响,在实际生产中,可以通过调整成形时的工艺参数提高汽车覆盖件的刚度.     

双层柱面网格扁壳的非线性稳定性分析

基于等效夹层壳思想的双层网格扁壳非线性弯曲理论,对双层柱面网格壳体在均布压力作用下的非线性稳定性问题进行研究,采用伽辽金方法求得了简支边界条件下双层柱面网格扁壳的非线性载荷-位移关系式和临界屈曲载荷的解析表达式,讨论网壳结构几何参数对临界屈曲载荷的影响.     

变形程度对曲面扁壳类汽车覆盖件刚度的影响研究

为进一步研究变形程度对曲面扁壳类覆盖件刚度的影响规律,并为提高和改善汽车覆盖件的刚度提供理论依据,建立了能够代表汽车覆盖件曲面特点的柱面扁壳、双曲扁壳件和球面扁壳试验模型.通过分析零件胀拉成形过程特点,得出零件变形程度与成形件特征之间的关系:板厚及成形件的回弹对刚度的影响较为显著,板厚越大、回弹越小,板材的刚度越好;由胀拉成形深度增加而引起的回弹量减少及变形程度增加而导致的试件成形均匀性的提高对刚度提高的贡献大于厚度减薄的影响.     

曲面扁壳类汽车覆盖件刚度的控制机制研究

为有效控制和提高汽车覆盖件的刚度,以能够代表汽车覆盖件曲面特点的柱面扁壳件和双曲扁壳件为研究对象,采用数值模拟和试验相结合的方法,深入分析零件在成形过程中拉深筋、拉深深度及压边力对刚度的影响规律,并通过分析扁壳件成形后应力应变分布特点,揭示工艺条件对刚度的影响机制.研究表明:刚度随着压边力的增大而增大,增设拉深筋有助于提高曲面扁壳件的刚度;刚度随着拉深深度的增加而增大;工艺条件的改变可以增大塑性应变量,减少残余应力,并减少回弹,提高刚度.     

柱面扁壳类覆盖件刚度的数值模拟研究

为更好地预测和评定板材覆盖件的刚度,进一步分析研究各影响因素对刚度的影响规律,以能代表汽车覆盖件曲面特点的柱面扁壳零件为研究对象,建立了柱面扁壳模拟件胀拉刚度的仿真分析模型.对柱面扁壳类覆盖件的成形、回弹以及刚度变形3个过程进行数值模拟研究,实验验证了本仿真系统的有效性和实用性,分析了压边力、回弹及约束形式对覆盖件刚度的影响规律.研究表明:增大压边力及回弹的减小都可以提高覆盖件的刚度;成形过程中,约束形式对刚度有重要影响,约束越大,刚度越大.     

模具型面工艺孔对面畸变的影响

为了研究成形凸模工艺孔对面畸变形态及大小的影响,以矩形双曲面扁壳为模型,采用拉深成形工艺方法获得了不同成形条件下的拉深件,利用油砂轮研磨双曲面扁壳拉深件表面,局部的畸变呈圆形暗坑,取暗坑直径(D)与工艺孔径(d)之比作为面畸变的评价指标,研究成形条件对面畸变的影响规律.研究结果表明:凸模型面工艺孔可以诱发双曲面扁壳拉深件面畸变;屈服强度越大、板料厚度越大、凸模型面弦高越小、压边力越小,面畸变越小.     

单层柱面网壳结构的抗震性能研究

本文以单层柱面网壳为研究对象,针对结构参数（矢跨比、荷载、长跨比和支承刚度等）,系统研究了各参数对结构自振特性及地震响应的影响,得出了四边支承的单层柱面网壳应同时考虑竖向地震和水平地震作用的结论,并建议用时程法进行抗震分析。文中结构对实际工程有指导意义。     

柱面网壳结构风致抖振响应研究

基于刚性模型风洞试验,在时域上对一柱面网壳结构进行风振响应计算,并细致分析了网壳结构在风荷载作用下的节点位移、单元应力、阵风响应因子和响应谱。结果表明,对于柱面网壳结构,受斜风作用时的工况为最不利工况,并且迎风侧端部的位移及单元应力最大;多个高阶振型参与振动;共振响应一般不可忽略,但对于起控制作用的响应,背景分量的贡献大于共振分量。     

扁壳广义协调曲面矩形元

本文从修正的扁壳胡海昌-鹫律原理泛函出发,引入两方面的广义协调条件(单元边界位移的积分型协调条件,膜应变与位移之间的积分型协调条件),使泛函退化为扁壳势能原理泛函,在此基础上导出一个具有二十个自由度的扁壳曲面矩形元。此单元对厚扁壳和薄扁壳都通用,不出现剪切闭锁和薄膜闭锁现象,具有良好的性能。     

平面应变轴对称压电圆柱壳的随机响应

提出求解随机激励轴对称压电圆柱壳响应的一种方法，并导出相应的解析表达式。首先给出压电圆柱壳在边界随机激励下的基本方程；然后通过位移与电势的变换，将随机激励变换到运动方程中；再利用Legendre多项式展开位移，应用Galerkin法化偏微分的运动方程为常微分方程组；最后根据随机振动理论，得到压电圆柱壳位移与加速度响应的均方值，由此可计算随机响应、分析有关因素的影响与机电耦合关系等。分析说明了存在的机电耦合项，及由此产生广义刚度的非对称性。     

正交异性扁薄球壳的非线性轴对称振动

给出了一种研究圆柱正交异性扁薄球壳非线性轴对称自由振动的新的时间模态方法。首先,使用变分法导出了决定振动频率的一对代数-微分方程。然后,利用作者提出的改进的修正迭代法求得了渐进解。这使此种壳体的非线性振动的进展获得扩充研究。     

Aircraft control surface deflection using RBF‐based mesh deformation

In this paper, mesh deformation based on radial basis function (RBF) interpolation is applied to the deflection of aircraft control surfaces. A confinement technique is presented, which locally restricts mesh deformation to the vicinity of the moving component and leaves the surfaces of other components unaffected. This technique is shown to have the potential to significantly reduce the CPU time necessary for evaluating the RBF interpolants. Motivated by the directionality of control surface deflection, the idea of treating each direction of the displacements separately is introduced. It is employed for the adaptive selection of centers, and the approach termed sequential uni‐variate center adaptation. It is shown to be more efficient for both solution and evaluation processes than the standard approach, in which the same set of centers is used for every direction. Furthermore, different data sites may be imposed for different directions. It is demonstrated that this enables sliding motion of the elements on the face of a mesh block. Thereby, large control surface deflections are possible, despite the presence of a small spanwise gap between control surface and parent component. These techniques are successfully applied to the deflection of aileron and horizontal tail of a generic fighter aircraft configuration. Copyright © 2011 John Wiley & Sons, Ltd.     

Plane stress and plate bending coupling in BEM analysis of shallow shells

In this paper the shear deformable shallow shells are analysed by boundary element method. New boundary integral equations are derived utilizing the Betti's reciprocity principle and coupling boundary element formulation of shear deformable plate and two‐dimensional plane stress elasticity. Two techniques, direct integral method (DIM) and dual reciprocity method (DRM), are developed to transform domain integrals to boundary integrals. The force term is approximted by a set of radial basis functions. Several examples are presented to demonstrate the accuracy of the two methods. The accuracy of results obtained by using boundary element method are compared with exact solutions and the finite element method. Copyright © 2000 John Wiley & Sons, Ltd.     

Non‐linear random response of laminated composite shallow shells using finite element modal method

This paper investigates the large‐amplitude multi‐mode random response of thin shallow shells with rectangular planform at elevated temperatures using a finite element non‐linear modal formulation. A thin laminated composite shallow shell element and the system equations of motion are developed. The system equations in structural node degrees‐of‐freedom (DOF) are transformed into modal co‐ordinates, and the non‐linear stiffness matrices are transformed into non‐linear modal stiffness matrices. The number of modal equations is much smaller than the number of equations in structural node DOF. A numerical integration is employed to determine the random response. Thermal buckling deflections are obtained to explain the intermittent snap‐through phenomenon. The natural frequencies of the infinitesimal vibration about the thermally buckled equilibrium positions (BEPs) are studied, and it is found that there is great difference between the frequencies about the primary (positive) and the secondary (negative) BEPs. All three types of motion: (i) linear random vibration about the primary BEP, (ii) intermittent snap‐through between the two BEPs, and (iii) non‐linear large‐amplitude random vibration over the two BEPs, can be predicted. Copyright © 2006 John Wiley & Sons, Ltd.     

Axisymmetric nonlinear analysis of shallow spherical shells by a combined boundary element and finite difference method

This paper is concerned with the development of the mixed boundary element method and finite element method for the analysis of spherical annular shells under axisymmetric loads. The boundary element techniques are used to solve the equilibrium equation of shells and the central difference operator is adopted to deal with the compatibility equations. Iterative techniques are used throughout the analysis procedure. A number of numerical examples are given in the paper to illustrate the validity of the present approach.