弹性地基梁损伤诊断研究

利用试验得到的振动参数评估结构的破损情况，是当前结构工程学科十分活跃的领域。由于弹性地基梁的振动模态受地基和梁两方面因素的影响，其损伤诊断问题变得十分复杂。本文通过对两靖自由弹性地基梁的灵敏性分析发现弹性地基梁的前两阶自由模态主要与地基有关，利用这一特性构造了两级识别的方法，并引入优化领域寻优能力极强的遗传算法进行识别，找到了令人满意的答案。     

简谐荷载作用下弹性地基上不可伸长梁的2次超谐共振响应研究

基于已建立的弹性地基上不可伸长梁的非线性动力学模型,利用梁的量纲归一化运动方程和多尺度方法求得梁2次超谐共振的幅频响应方程和位移的二次近似解。进而,运用梁的幅频响应曲线对其超谐共振响应特性进行研究,同时分析了弹性地基模型、Winkler参数、外激励幅值、边界条件等对该共振响应的影响效应。结果表明:弹性地基模型中剪切参数的引入增大了梁2次超谐共振响应的幅值和多值区域;弹性地基Winkler参数的增加会抑制系统的共振响应,但同时会增加系统动力响应的软弹簧特性;在外激励幅值较小的情况下,系统共振响应未展现出明显的非线性特征;边界约束对弹性地基剪切参数作用于梁2次超谐共振响应的效应有显著影响,可在一定程度上改变系统响应幅值及多值区域。     

弹性地基上Euler-Bernoulli梁的热屈曲模态跃迁特性

采用解析方法研究了置于线性弹性地基上的Euler-Bernoulli梁在均匀升温载荷作用下的临界屈曲模态跃迁特性;分别在两端不可移简支和夹紧边界条件下,给出了弹性梁屈曲模态跃迁点的地基刚度值以及屈曲载荷值的精确表达式,并分析了模态跃迁特点.结果表明:随着地基刚度参数值的增大临界屈曲模态通过跃迁点从低阶次向高阶次跃迁;两端简支梁的模态跃迁具有突变特性,而两端夹紧梁的模态跃迁则是一个缓慢变化过程,它是通过端截面的弯矩或曲率的正负号改变实现的.     

考虑水平摩阻力与竖桩支撑的弹性地基梁

考虑水平摩阻力,建立了任意对称荷载和具有竖桩支撑的有限长弹性地基梁的平衡微分方程.进行了合理的位移形函数假设,利用Galerkin方法建立了非线性代数方程组并采用迭代法进行求解,得到了具有竖桩支撑弹性地基梁的位移和内力解.通过实例计算可知,水平摩阻力对弹性地基梁的挠度和剪力影响很小,而对弯矩和轴力影响很大;竖桩支撑可以很大程度地改变弹性地基梁的变形和受力状态,合理地布置竖桩可以大大地减小弹性地基梁的挠度和弯矩.     

层状分数阶黏弹性饱和地基与梁共同作用的时效研究

饱和地基与梁共同作用问题的研究在力学领域及工程界都具有重要意义. 采用分数阶Merchant模型研究饱和地基的流变固结, 该模型比常用整数阶黏弹性模型更能精确反映地基的时变特征. 基于层状正交各向异性黏弹性饱和地基的固结解答, 采用有限元法与边界元法耦合的方法, 研究梁与分数阶黏弹性饱和地基的共同作用问题. 依据Timoshenko梁理论将梁离散为若干单元, 进而得到梁的总刚度矩阵方程; 将黏弹性地基固结问题的精细积分解答作为边界积分的核函数, 采用边界元法建立地基柔度矩阵方程; 结合梁与地基接触面的位移协调条件以及力的平衡条件, 通过有限元法与边界元法的耦合, 最终求得层状分数阶黏弹性饱和地基与Timoshenko梁共同作用的解答. 将本文地基退化为Kelvin地基进行计算, 并与已有文献中的算例进行对比, 二者具有很好的一致性. 在此基础上, 探讨分数阶次和地基成层性对梁与黏弹性饱和地基共同作用的影响. 结果表明: 分数阶次高的黏弹性饱和地基的固结速率明显更快; 对于层状地基, 加固表层土体能有效控制地基整体沉降, 并减小差异沉降. 实际工程中, 应充分考虑饱和地基流变及土体分层性的影响, 以准确分析梁与地基的共同作用过程.      

弹性地基梁的一种解法

由于弹性地基梁与地基连续接触,因而成为一无穷多次超静定结构,且又必须考虑地基的变形,这就使问题的求解相当冗繁.尤其在受载复杂时,计算更感不便.本文通过积分变换,提出一种解法,使其在公式推导与解题程序上均有所简化,并能对长梁、短梁进行统一描述.(一)基本公式推导考察图1所示弹性地基梁,假定全梁抗弯刚度 EJ为常数,并认为地基符合温克尔假设.这样,该梁的地 ....     

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由于弹性地基梁与地基连续接触,因而成为一无穷多次超静定结构,且又必须考虑地基的变形,这就使问题的求解相当冗繁.尤其在受载复杂时,计算更感不便.本文通过积分变换,提出一种解法,使其在公式推导与解题程序上均有所简化,并能对长梁、短梁进行统一描述.(一)基本公式推导考察图1所示弹性地基梁,假定全梁抗弯刚度 EJ为常数,并认为地基符合温克尔假设.这样,该梁的地     

Winkler弹性地基上梁的精化理论

将Cheng精化理论推广到winkler弹性地基上梁的研究当中,对winkler弹性地基上的梁进行了精确的分析,给出其精化理论。首先将板内的位移利用中面上位移及其沿梁厚方向的梯度表示出来,并获得梁内应力张量。再利用winkler弹性地基条件和Lur'e算子方法,获得弹性地基上梁的控制方程。若略去控制方程中的高阶项,与弹性地基上欧拉-伯努利梁的挠度控制方程一致。     

考虑轴向力的双参数弹性地基有限长梁的静力问题

探讨轴向荷载对双参数地基梁弯曲的影响,以最小势能原理为基础,采用变分法推导了双参数地基上承受轴向力的梁的控制微分方程及边界条件,并明确了衰减参数γ需要满足的方程。对地基梁的参数γ进行了迭代,给出了双参数弹性地基上承受轴向力的有限长梁的内力及变形的求解方法。结果表明:轴向力的存在,使得地基梁的跨中挠度、最大弯矩、转角均有所增大;轴向力对地基梁的剪力有所影响,但影响程度并不大。本文计算方法准确可行,为双参数弹性地基模型的推广应用奠定了基础,具有广阔的应用前景。     

分数阶黏弹性Pasternak地基上两端固支Timoshenko梁的动力响应

本文研究了放置在黏弹性Pasternak地基上的Timoshenko梁在移动载荷作用下的动力响应行为．首先,引入分数阶导数,将整数阶标准固体黏弹性地基模型推广为分数阶标准固体黏弹性模型．对于Pasternak地基,考虑压缩层是黏弹性的而剪切层仍是弹性的情况,给出了地基反作用力．然后,求解了Timoshenko梁的自由振动解,获得含黏性耗散信息的复固有频率及振型函数．在此基础上用振型叠加法分析了在移动简谐荷载作用下梁的位移响应．在数值算例中,给出了不同分数阶导数、地基黏性系数以及载荷移动速度下梁的动态响应,讨论了黏弹性地基对梁的动态响应的影响规律．     

Mesh regularization for an ALE code based on the limitation of the Lagrangian mesh velocity

The Lagrangian approach is usually used for the simulation of flow with strong shock waves. Moreover, this approach is particularly well suited to treatment of material interfaces in the case of multimaterial flows.Unfortunately, this formulation leads to very large deformations in the mesh. The arbitrary Lagrangian‐Eulerian method overcomes this drawback by using a mesh regularization that is based on an analysis of cell geometry. The regularization step may be considered as a method used to correct the nonconvex and potentially tangled cells that constitute the mesh. In this paper, we present a new approach to mesh regularization. Instead of using a purely geometric criterion, we propose that the mesh evolution is computed on the basis of the flow vorticity. This approach is called the large Eddy limitation method, and it is aimed here to be used in finite volume direct arbitrary Lagrangian‐Eulerian methods. The large Eddy limitation method is general, which means that it is not restricted to applications in the finite volume framework dedicated to fluid flow simulation; for instance, it could also be naturally applied to the finite element framework.     

DISCRETE AND CONTINUUM MODELLING OF GRANULAR FLOW

This paper analyses three popular methods simulating granular flow at different time and length scales： discrete element method （DEM）, averaging method and viscous, elastic-plastic continuum model. The theoretical models of these methods and their applications to hopper flows are discussed. It is shown that DEM is an effective method to study the fundamentals of granular flow at a particle or microscopic scale. By use of the continuum approach, granular flow can also be described at a continuum or macroscopic scale. Macroscopic quantities such as velocity and stress can be obtained by use of such computational method as FEM. However, this approach depends on the constitutive relationship of materials and ignores the effect of microscopic structure of granular flow. The combined approach of DEM and averaging method can overcome this problem. The approach takes into account the discrete nature of granular materials and does not require any global assumption and thus allows a better understanding of the fundamental mechanisms of granular flow. However, it is difficult to adapt this approach to process modelling because of the limited number of particles which can be handled with the present computational capacity, and the difficulty in handling non-spherical particles. Further work is needed to develoo an aoorooriate aooroach to overcome these problems.     

在线整周模糊度快速解算法

本文介绍了利用差分GPS求解的基线向量,并用此基线向量来确定载体姿态的算法。重点介绍了一种在此特定的应用背景下整周模糊度的快速解算法。经实际数据检验,本方法能快速准确的确定整周模糊度,且解算出的载体姿态具有较好的精度。     

结合数码显微镜的数字散斑相关方法精度分析及应用

结合数字散斑相关方法和一种新型的显微镜数码显微镜,提出了一种测量多晶材料晶粒尺度面内变形的新方法,并通过零变形校准实验、重聚焦实验和平移实验等一系列验证实验分析了该方法的精度和实用性.作为应用实例,对一种镍基合金试件进行了单向拉伸和疲劳实验,得到了晶粒尺度下具有较大应变梯度的应变分布图像.结果表明,该方法能够得到精确的位移测量数据,是一种理想的测量晶粒尺度变形的光测方法.     

横观各向同性轴对称问题的加权残数法及其工程应用

利用文[1,5]的理论,本文提出用两个调和函数的方法求解横观各向同性的轴对称问题,将它引入加权残数法,推得了一系列简洁的边界型最小二乘配法公式,就结构工程和岩土工程的两个例题作了计算,得到了有用的结论。本文的方法比列赫尼茨基的重调和函数法更为简便。     

矩形板结构损伤的分区域神经网络识别方法

通过引入LM优化算法,针对矩形薄板中对称结构的损伤识别问题,提 出了一种基于神经网络的分区域分步识别方法. 对于预测输出量比较多且对预测精度要求比 较高的问题,常会出现网络训练时收敛速度慢、网络预测精度低,并且当网络训练达到目标 误差时,输出的预测量中常有某个输出量的误差还很大的情况. 针对这些问题,利用选 取的组合输入参数,提出了基于神经网络的分区域识别方法. 通过对悬臂板结构的数值模拟 结果表明：提出的分区域识别方法对结构损伤的分区和预测是可行和有效的, 其预测精度要明显的高于只用单个网络的预测结果,并且预测子网络对损伤的位置和程度是 同步输出的,从而避免了传统分步识别理论中子网络过多的问题.     

一种计算复合材料等效弹性性能的有限元方法

在最小二乘意义下提出了一种计算复合材料等效弹性性能的有限元方法.这种方法由于考虑了等效弹性张量各分量之间的耦合关系,所求得的等效弹性常数比传统方法更可靠,可适用于求解含任意形状的夹杂和夹杂物问题.通过算例计算了在不同弹性模量对比度下两相复合材料的等效弹性性能,并与相关的理论及数值结果进行了比较,结果表明,利用该方法计算含夹杂复合材料等效弹性常数是可行的.     

FATIGUE PROPERTY BASED ON NOTCHED SPECIMEN TESTS

缺口件疲劳问题的研究日益引起各国学者的重视. 局部应力-应变法以其简单性在工程中得到了广泛应用, 该方法通常会得到偏于安全的结果. 引入疲劳缺口因子代替弹性应力集中因子针对缺口疲劳进行研究, 仍未能从本质上改善预测结果的准确性. 考虑到"热点应力" 附近的相对应力梯度, 提出了应力梯度法研究缺口件疲劳问题, 这一概念亦被用于应力场强度方法中, 如何准确确定损伤区域是应力场强度方法需要解决的问题. 临界距离理论可将Neuber 律、Peterson 方法及应力场强度方法进行有效统一, 同时有限元方法的发展进一步支持了该理论. 目前, 该方法在高周疲劳研究中取得了较好的效果, 但对低周疲劳寿命预测的有效性仍需进一步的验证.     

Numerical simulation of ground water flow via a new approach to the local radial point interpolation meshless method

A novel approach to local radial point interpolation meshless (LRPIM) method is introduced to investigate the influence of leakage on tidal response in a coastal leaky confined aquifer system, based on a local weighted residual method with the Heaviside step function as the weighting function over a local sub-domain. The present approach is a truly meshless method based only on a number of randomly located nodes. In this approach, neither global background integration mesh nor domain integration is needed. Radial basis functions (RBFs) interpolation is employed in shape function and its derivatives construction for evaluating the local weak form integrals. Due to satisfaction of kronecker delta property in RBF interpolation, no special treatment is needed to impose the essential boundary conditions. In order to obtain the optimum parameters, shape parameters of multiquadrics (MQ)-RBF are tuned and studied. The leakage has a significant impact on the tidal behaviour of the confined aquifer. The numerical results of this research indicate that both tidal amplitude of groundwater head in the aquifer and the distance over which the aquifer can be disturbed by the tide are considerably reduced by leakage. The novelty of the approach is the use of a local Heaviside weight function in the LRPIM which does not need local domain integration and only integrations on the boundary of the local domains are needed. Therefore, in this research a new local Heaviside weight function has been proposed. Numerical results are presented and compared with the results of analytical solution. It is observed that the obtained results agreed very well with the results of analytical solution. The numerical results show that the use of a local Heaviside weight function in the LRPIM is highly accurate, fast and robust. It is also noticed that this novel meshless approach using MQ radial basis is very stable.     

An orthogonal self-stress matrix for efficient analysis of cyclically symmetric space truss structures via force method

The analysis of structures is normally carried out through displacement method while the force method is considered as an alternative approach for this purpose and used on occasion. The generation of compatibility conditions (the transpose of self-stress matrix) is one of the major and complicated parts of any structural analysis using force method. In this paper, an efficient method is proposed for producing orthogonal self-stress matrix related to space truss structures with cyclic symmetry. This is actually performed by eigen-decomposition of a special matrix having the same null basis as in equilibrium matrix. Then, the advantages of the obtained compatibility conditions are demonstrated with respect to different formulations such as standard force method, eigen force method and integrated force method. Finally, the efficiency of the presented method is comprehensively compared with three well-known numerical methods and tested on a set of practical examples. The results indicate clearly the significant superiority of the proposed approach in terms of both computational time and the accuracy of the results.