各向异性油藏渗流的有限元数值模拟

为使模拟计算更加接近实际情况,将油水井作为油藏的内边界处理,建立各向异性油藏单相流体渗流问题的有限元方程。在此基础上利用八节点四边形等参元,结合伽辽金有限元方法对渗流方程在空间域上离散,采用全隐式时步格式在时间域上离散。对单相流体的平面单向流、各向异性油藏平面径向流的有限元解和解析解进行对比,得到了地层中不同位置处的压力变化和产量变化规律。研究结果表明,有限元模拟的结果与解析解相比很接近,这充分说明所建立的模型和计算程序是正确的。该研究成果可用来指导油井的实际生产,对预测油井的产能变化具有重要意义。     

Vibration and buckling of thin-Walled structures by a new finite strip

This paper presents the application of a new finite strip to the analysis of folded-plate structures. The displacement function of a flat shell finite strip is made up of two parts, namely, the two in-plane displacement interpolations and the out-of-plane displacement interpolation. Each of the three displacement components is interpolated by a set of computed shape functions in the longitudinal direction and, as usual, one-dimensional shape functions in the transverse direction. Only standard beam shape functions are involved in the longitudinal computed shape functions. When compared with other finite strips, the present finite strip is relatively simple in dealing with boundary and internal support conditions. In addition, the method can be easily implemented by incorporating a standard finite strip program with a continuous-beam program. The computation of the stiffness matrix involves no numerical integration. To verify the accuracy and efficiency of the new finite strip, a few numerical experiments are conducted in which the present finite strip results are compared with those using other finite strips and/or finite elements for the vibration and buckling of folded-plate structures with varying complexity.     

开椭圆孔板的应力分析

运用复变函数保角变换求解无限大板开有椭圆孔时的孔边界处的应力分布规律,通过对开椭圆孔有限板的有限元分析,找出开椭圆孔有限板的应力分布与开椭圆孔无限板的应力分布的关系,达到用开孔无限板求解开孔有限板的目的。     

不同方法掺细颗粒饱和砂土的动强度试验研究

对细颗粒含量为21%,23%,25%,27%,29%的混合掺细颗粒砂土试样进行了动强度试验,对三种分层掺细颗粒试样的动强度曲线的分析研究,得出从单层掺细颗粒到两层掺细颗粒,动强度的变化不明显,从两层掺细颗粒到三层掺细颗粒,动强度增加约为3%,对比混合掺细颗粒与分层掺细颗粒,分层的方法效果不明显。     

Analysis of thin-walled structures by finite strip and finite layer methods

The finite strip and finite layer methods are powerful tools for the analysis of thin-walled structures. In this paper, the finite strip method is applied to study the behavior of cold-formed steel beams including webs with longitudinal stiffeners. Comparisons are made with AISI specifications and published data. The finite layer method is used to investigate the buckling behavior of sandwich panels with thin facings and rigid foam cores. Effects of variable core stiffnesses (due to uneven curing, etc.) on the buckling strength are quantified and presented.     

Finite element formulation and application of poroelastic generalized plane strain problems

A generalized plane strain finite element is developed for the analysis of poroelasticity problems. The validity and accuracy of the special element is demonstrated by analyzing inclined borehole problems in isotropic and transversely isotropic poroelastic materials. For the former, comparison is made with an analytical solution and the latter, with a three-dimensional finite element solution. A substantial reduction in computational effort is realized for the generalized plane strain finite element, as compared to the three-dimensional finite element. This is achieved without sacrificing the accuracy and the ability to account for the three-dimensional material anisotropy and far field stress components.     

SYR200型旋挖钻机桩架整体有限元分析中销轴连接模型的研究

对旋挖钻机桩架整体有限元分析中的关键件——销轴连接的有限元模型进行了深入研究,并提出了实用而精确的有限元模型。这种模型适用性强,可以把桩架的各个结构连接在一起形成一个整体的有限元模型,在很大程度上提高了有限元分析结构的精度。使用这种模型对SYR200旋挖钻机桩架进行了整体有限元分析,分析对钻孔机桩架的结构设计有指导意义。     

Analysis and design of cold-formed steel channels subjected to combined bending and web crippling

The channel failures due to combined bending and web crippling may occur at the highly concentrated interior loading when there is no load stiffener in cold-formed thin-walled steel beams. This paper presents accurate finite element models to predict the behavior and ultimate strengths of cold-formed steel channels subjected to pure bending as well as combined bending and web crippling. Both geometric and material nonlinearities are considered in the finite element analysis. The nonlinear finite element models are verified against experimental results of cold-formed steel channels subjected to pure bending as well as combined bending and web crippling. The finite element analytical results show a good agreement with the experimental results in terms of the ultimate loads and moments, failure modes and web load-deformation curves thus validating the accuracy of the finite element models. The verified finite element models are then used for an extensive parametric study of different channel dimensions. The channel strengths predicted from the parametric study are compared with the design strengths calculated from the North American Specification for cold-formed steel structures. It is shown that the design rules in the North American Specification are generally conservative for channel sections with unstiffened flanges having the web slenderness ranged from 7.8 to 108.5 subjected to combined bending and web crippling. It is demonstrated that the nonlinear finite element analysis by using the verified finite element models against test results is an effective way to predict the ultimate strengths of cold-formed thin-walled steel members.     

地下工程开挖计算的广义有限元法

基于传统有限元理论，将每个结点位移的Lagmnge型插值空间推广为具有任意多个广义位移的函数展开式，在不增加结点个数的前提下，仅通过提高结点插值函数的阶数，达到提高有限元精度的目的，建立了三维广义8结点等参单元和一维广义杆单元。首先推导单元的广义形函数，并给出单元的位移模式；然后进一步推导单元应变矩阵和劲度矩阵以及单元等效荷载列阵等有限元列式。针对地下工程开挖问题，提出联合运用广义有限元和传统有限元，在开挖边界附近和加锚区围岩采用高精度的广义有限元，在远离开挖区域岩体采用高效率的传统有限元，既改善有限元的计算精度，又提高有限元的计算效率，并探讨了广义有限元的程序实施细则。通过对若干算例及工程实例的计算，其结果表明广义有限元法的优越性，为地下工程开挖计算提供了一种合理的数值方法。     

Dual analysis of frictionless problems by displacement and equilibrium finite elements

The paper deals with the duality of the frictionless contact problem in the sense of convex analysis, contact between an elastic body and a rigid foundation under small deformation conditions. A new method using equilibrium finite elements is proposed. Virtual work theorems are first shown under variational equality forms. Fenchel-Rockafellar duality and Arrow-Hurwicz duality are used to deduce four variational principles of elastic bodies in contact. The boundary contact finite elements are then formulated from these theoretical foundations of convex analysis. A new interpretation of equilibrium finite elements and their associated boundary contact finite elements is described. Lastly, the different contact finite elements, their properties and numerical results are described. Agreement with analytical solutions is satisfactory.     

Finite element modelling of plate girders with web openings

This paper is concerned with a finite element model to predict the behaviour and ultimate load of plate girders with web openings. The finite element package is used to model the plate girders with web openings. Accuracy of the model is assessed by applying it to plate girders tested earlier by other researchers. Comparison of analytical results with the available experimental results for yielding patterns, ultimate load values and load–deflection relationships show good agreement between the finite element and experimental results thus validating the accuracy of the proposed model. The proposed finite element method was extended to carry out a parametric study. The study covered parameters such as web slenderness and flange stiffness.     

Dynamic analysis of partially prismatic thin-walled structures

A mixed-mode method is investigated for the dynamic analysis of partially prismatic structures, such as box girders with intermediate diaphragms and supports, or with variable-depth webs. Thus the prismatic ‘main structure’ is discretised by finite strips, and the non-prismatic ‘sub-structure’ by finite elements. After dynamic reduction of the finite element degrees of freedom, advantage may be taken of the finite strip harmonic expansions in determining mode shapes. The method is tested by a variety of examples. Thus for structures with transverse substructures (e.g. diaphragms), the method is shown to be successful, being up to an order of magnitude faster than finite elements. However, for structures with longitudinal substructures (e.g. variable-depth webs) the method is shown to be unreliable. This is because for such structures, approximations in the dynamic reduction procedure are found to be significant.     

PVA-ECC薄板四点弯曲有限元分析

利用有限元软件建立了聚乙烯醇纤维增强超高韧性水泥基复合材料(PVA-ECC)薄板四点弯曲的有限元模型,并与已有PVA-ECC薄板四点弯曲试验进行比较,验证了有限元模型的有效性.从单元选取、材料属性定义、网格划分、接触定义、施加边界条件、荷载等方面阐述了有限元建模过程,为后续PVA-ECC有限模型的建立提供一定的参考.     

Buckling of thin flat-walled structures by a spline finite strip method

A method of buckling analysis of thin flat-walled structures of finite length subjected to longitudinal compression and bending, transverse compression as well as shear is described. The analysis uses the spline finite strip method and allows for boundary conditions other than simply supported ends as required in the semi-analytical finite strip method of buckling analysis.Convergence studies with increasing numbers of section knots are described for plates in compression, bending and shear, and for long columns with different support conditions subjected to compression. A buckling analysis of a stiffened plate subjected to compression and shear is compared with results from a finite element analysis.     

土—基础共同作用分析的有限元/无限元耦合方法模型研究

为考虑土—基础共同作用，建立了有限形无限元耦合方法分析模型。通过对同一结构体系分别应用有限元理论和有限形无限元耦合方法比较，研究了有限形无限元耦合体系中有限元范围在水平与竖向区域的不同取值对计算结果的影响，从而确定了有限元区域的计算范围。结果表明，有限形无限元耦合方法对于研究共同作用问题具有较高的精度和显著的经济性。     

基于二阶锥规划理论的有限元强度折减法及应用

针对岩土体稳定性问题,常用的方法有极限平衡法和有限元强度折减法等。传统的有限元强度折减法通常需设置很大的最大允许非线性迭代次数(如200或500),计算耗时严重,此外,采用的平衡迭代和应力积分算法可能导致岩土体塑性区计算不够准确,进而影响稳定性分析结果。提出一种二阶锥规划有限元强度折减法,该方法基于Hellinger–Reissner混合变分原理和有限元法,将岩土体弹塑性问题构造成基于有限元框架的二阶锥规划问题,结合强度折减技术来分析岩土体稳定性。将该新方法应用于平面应变岩土体稳定性分析,结果表明:与传统的有限元强度折减法相比,新方法结果可靠,但其计算效率更高,所获得的塑性区更加平滑。     

工科专业“有限单元法及程序设计”课程改革新思路

在对当前工科专业有限元教学现状分析的基础上,提出了工科专业本科和研究生阶段统筹考虑的＂有限元法及程序设计＂课程改革新思路。其主要思想是,将权威开源代码与有限元理论学习相融合,通过＂代码＂学习＂理论＂,通过＂理论＂理解＂代码＂,让学生＂学得懂,对得上,可复用＂,既扎实掌握有限元理论,又熟练掌握一套终身受益的程序代码,从而切实提高有限元教学效果和质量,最终为学生今后工作和继续深造中使用有限元打下坚实而有用的基础。     

初弯矩作用下预应力碳纤维布加固RC梁数值分析

通过利用大型通用软件ANSYS,对钢筋混凝土(RC)试件梁的碳纤维布粘贴方案的抗弯性能进行了非线性有限元分析。对卸载或不卸载时预应力碳纤维布加固梁进行仿真分析,提出了利用单元生与死实现不卸载时加固的方法,以及使用升温法施加预应力。使用ANSYS分析的结果与实验分析结果吻合较好,从而此方法可在一定程度上有效代替试验分析方法。     

钢筋混凝土蜂巢芯空心楼盖的有限元分析

建立与试验相同尺寸的有限元模型,模拟在弹性阶段受力,将得到的有限元计算结果与试验结果进行比较,并建立了实心板、密肋板的有限元模型,进行对比得出结论:蜂巢芯空心楼盖与密肋楼盖相比,在自重增加很小的情况下,挠度降低很多,说明这种结构形式具有较好的刚度。蜂巢芯空心楼盖与实心楼盖相比,在挠度增长不多的情况下,自重大幅度下降,可以大大节约混凝土的用量。因此这种结构形式在工程中应用的前景极为广阔。     

变截面门式钢刚架结构体系平面内稳定研究

本文论述了变截面梁单元平面内稳定分析方法,比较了不同类型梁单元（等截面梁单元、普通位移模式变截面梁单元、积分位移模式变截面梁单元）对变截面刚架平面内稳定分析的差异。利用上述有限元法,给出了对称刚架变截面柱计算长度系数的实用计算公式,并分析了横梁轴力对刚架柱稳定的影响。