新型三角形弹簧质点模型及弹簧参数确定

针对任意单元形状和材料参数,通过引入附加节点和附加弹簧建立了一种三角形弹簧质点模型.首先给出弹簧刚度参数及附加节点坐标的解析公式,以实现有限元模型和弹簧质点模型三角形单元刚度矩阵的精确相等;然后考虑弹簧质点模型中可能出现的负刚度弹簧,进一步完善了弹簧质点模型形变计算方法.基于平面柔性体的数值模拟结果表明,文中提出的弹簧质点模型和形变计算方法精度好、效率高,且更具通用性.     

雾化器转轴振动特性研究

在考虑陀螺力矩、转动惯量和剪切效应等影响因素下,采用Timoshenko梁理论并结合传递矩阵法给出了雾化器转轴的振动特性的计算方法.数值仿真部分采用二节点梁单元建立了雾化器转轴的有限元模型,并进行模拟,其结果验证了本文方法的有效性和高精度,讨论了转速、雾化轮质量以及陶瓷约束刚度等参数对雾化器转轴振动特性的影响.     

基于四边形面积坐标法的广义协调薄板单元

为克服等参坐标的缺点,采用四边形面积法构造一系列4节点12自由度的广义协调任意面积坐标四边形薄板(Area-coordinate Quadrilateral Plate,AQP)单元.对广义协调条件、边界位移场和试函数的选取规律进行深入探讨.该系列单元克服等参单元易网格畸变的缺点,在推导过程中引入广义位移的特征矩阵、节点位移的特征矩阵以及转换矩阵的概念,以使推导过程简单化、通用化.数值算例表明,此方法通用性强、易于程序化,所构造的单元自由度少、效率和精度较高.     

关于有限单元法中数值积分公式的两点注记

在有限单元法中,尤其是在选用参数型单元时,广泛应用数值积分去导出单元的荷载列阵和劲度矩阵.而在三角形单元、三棱柱单元或四面体单元中,积分公式常常采用借助自然坐标表示的Hammer积分公式:     

一种用于规则QC-LDPC码的高效译码方法

针对一类规则QC-LDPC码,提出一种高效的Log-BP译码方法,通过矩阵分裂,将原监督矩阵分裂成多个小矩阵,将原本的校验节点更新运算拆分成多次处理,以降低log-BP迭代运算的复杂度,给出该方法的迭代运算顺序。与现有的log-BP译码方法相比,该方法在相同的码速率下,校验节点运算单元与变量节点运算单元总规模减小了1/3;在相同的硬件资源下,译码速率提高了1/3,且校验节点运算单元与变量节点运算单元结构趋于对称,有利于设置更少的流水线级数、获得更好的时钟性能。     

一种网格和节点同步生成的二维Delaunay网格划分算法

应用Lawson算法对网格的Delaunay性质进行维护,利用单元尺度场控制生成网格的疏密分布;找到任一不满足尺度场要求的单元,在其可插度最大的边上按一定法则插入新节点,加密网格,实现内节点的生成与网格划分同步进行.该算法避免了搜寻包含三角形的过程,提高了效率.通过多次划分实验表明,该算法的时间复杂度约为O(N1.2).同时,由于在不满足单元尺寸要求的单元边上插入新节点,直接对单元的边长进行控制,使得网格的质量和自适性更加良好.     

基于振动信号的传感器节点性能测试系统设计

传感器节点用于采集轮轨作用下钢轨的振动信号以分析钢轨振动特性。为了测试传感器节点的工作性能,设计并实现了能提供稳定振动信号的测试系统。测试系统基于MSP430单片机,由控制单元、激振器、简支梁结构以及监控软件组成。实验表明：在给定加载条件下测试系统可稳定提供10N的激振力,产生峰值为93×10－6的动态应变和97 gn 的振动加速度。通过分析采集数据的时频特性,可以有效发现故障节点。     

空间薄壁梁单元面向对象程序的实现

针对传统有限元分析软件主要面向过程设计,其可维护性和可扩展性等较差的问题,基于面向对象程序设计方法,建立具有内部节点的空间薄壁截面梁单元模型,给出线弹性空间薄壁梁单元的UML类图,介绍矩阵类、截面类、材料类、节点类、单元类和结构类等6种类成员的主要属性和方法.用C#编制相应的有限元程序,通过T形框架算例比较和验证其位移和弯曲转角计算值、理论解和ANSYS的BEAM 189梁单元的数值解,结果表明该程序精度良好,可用于空间薄壁结构的有限元分析.     

平面任意区域四边形网格自动生成的一种方法

在改进节点连接法的基础上，提出了一种平面任意区域的有限元网格全自动剖分方法，既能快速生成四边形单元网格，也能生成三角形单元网格；     

改进波前法初始布点的高质量CVT网格生成

利用改进波前法(AFT)生成网格初始布点和Voronoi质心块(CVT)网格优化技术,在任意平面域获得了几乎是等边三角形的高质量非结构化网格.该算法在边界网格的基础上将离散边界作为初始波前,通过规范边长将网格单元分为合格与不合格单元,在不合格单元侧根据网格尺寸函数的要求构造新的最优点集,并过滤后进行Delaunay插入.利用CVT技术进一步调整网格节点位置,结合局部边交换,获得了网格几何平均质量在0.985以上的几乎是等边三角形的高质量网格.     

NORMALIZED ELEMENT NODE TOPOLOGICAL MATRIX OF FINITE ELEMENT MESHES

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Insight into 3-node triangular shell finite elements: the effects of element isotropy and mesh patterns

In this paper, we study the convergence characteristics of some 3-node triangular shell finite elements. We review the formulations of three different isotropic 3-node elements and one non-isotropic 3-node element. We analyze a clamped plate problem and a hyperboloid shell problem using various mesh topologies and present the convergence curves using the s-norm. Considering simple bending tests, we also study the transverse shear strain fields of the shell finite elements. The results and insight given are valuable for the proper use and the further development of triangular shell finite elements.     

Determining invertible two and three dimensional quadratic isoparametric finite element transformations

This paper presents an algorithm determining the invertibility of any planar, triangular quadratic isoparametric finite element transformation. Extensions of the algorithm to three-dimensional isoparametric finite element transformations yield conditions which guarantee invertibility of 10-node tetrahedra and 8-node bricks.     

Use of lst elements in elastic-plastic solutions

Elastic-plastic finite element analyses using the Mises and Tresca yield conditions have become quite well-known since their introduction several years ago. Constant strain triangular (CST) elements have generally been utilized in these solutions.A 6-node linear strain triangular (LST) element with the capability of modeling partial plasticity is presented in this paper. A plane stress tensile specimen with a 90 degree notch subjected to a monotonically increasing load is solved by both the CST and LST element models within the inelastic range. It is shown that although the growth of plastic regions predicted by LST elements is smoother and more accurate when compared with those due to CST elements, there is a penalty to be paid in terms of the needed computer time. Consequently, unless very accurate strain and stress distributions are required in a specific problem, the use of CST elements in elastic-plastic analyses should be preferred.     

A simple displacement-based 3-node triangular element for linear and geometrically nonlinear analysis of laminated composite plates

A simple displacement-based 3-node, 18-degree-of-freedom flat triangular plate/shell element LDT18 is proposed in this paper for linear and geometrically nonlinear finite element analysis of thin and thick laminated composite plates. The presented element is based on the first-order shear deformation theory (FSDT), and the total Lagrangian approach is employed to formulate the element for geometrically nonlinear analysis. The deflection and rotation functions of the element boundary are obtained from the Timoshenko’s laminated composite beam functions, hence convergence to the thin plate solution can be achieved theoretically and shear-locking problem is avoided naturally. The plane displacement interpolation functions of the Airman’s triangular membrane element with drilling degrees of freedom are taken as the in-plane displacements of the element. Numerical examples demonstrate that the present element is accurate and efficient for linear and geometrically nonlinear analysis of thin to moderately thick laminated composite plates.     

An efficient facet shell element for corotational nonlinear analysis of thin and moderately thick laminated composite structures

In the present work, an efficient facet shell element for the geometrically nonlinear analysis of laminated composite structures using the corotational approach is developed. The facet element is developed by combining the discrete Kirchhoff-Mindlin triangular bending element (DKMT), and the optimal membrane triangular element (OPT). The membrane-bending coupling effect of composite laminates is incorporated in the formulation, and inconsistent stress stiffness matrix is formulated. Using corotational formulation and the proposed facet element, some example laminated composite structures with geometric nonlinearity are analyzed, and the results are compared with those found using other facet elements.     

高次三角形单元的可视化显示

高次三角形单元在有限元计算中起着重要作用，本文提出一种画高次三角形单元云图的新方法。自然坐标系中的等腰直角三角形母元被均匀划分为N^2个等腰直角子三角形，根据映射到屏幕上的子三角形形心处的温度计算颜色，然后进行填充。实践表明，文中方法十分有效。     

8- and 12-node plane hybrid stress-function elements immune to severely distorted mesh containing elements with concave shapes

By simply improving the first version of hybrid stress element method proposed by Pian, several 8- and 12-node plane quadrilateral elements, which are immune to severely distorted mesh containing elements with concave shapes, are successfully developed. Firstly, instead of the stresses, the stress function ? is regarded as the functional variable and introduced into the complementary energy functional. Then, the fundamental analytical solutions (in global Cartesian coordinates) of ? are taken as the trial functions for 2D finite element models, and meanwhile, the corresponding unknown stress-function constants are introduced. Thus, the resulting stress fields must be more reasonable because both the equilibrium and the compatibility relations can be satisfied. Thirdly, by using the principle of minimum complementary energy, these unknown stress-function constants can be expressed in terms of the displacements along element boundaries, which can be interpolated directly by the element nodal displacements. Finally, the complementary energy functional can be rewritten in terms of element nodal displacement vector, and thus, the element stiffness matrix of such hybrid stress-function (HS-F) element is obtained. This technique establishes a universal frame for developing reasonable hybrid stress elements based on the principle of minimum complementary energy. And the first hybrid stress element proposed by Pian is just a special case within this frame. Following above procedure, two 8-node and two 12-node quadrilateral plane elements are constructed by employing different fundamental analytical solutions of Airy stress function. Numerical results show that, the 8-node and 12-node models can produce the exact solutions for pure bending and linear bending problems, respectively, even the element shape degenerates into triangle and concave quadrangle. Furthermore, these elements do not possess any spurious zero energy mode and rotational frame dependence.     

极大熵条件下的动态搜索优化图象重建方法

提出一种满足多种准则的动态搜索优化图象重建方法。从图象场的本质出发，设立了３个准则函数。熵函数的导数是非线性的，本文将其变换为近似的线性公式以获得迭代公路。动态搜索则尽可能避免很多算法在迭代过程中对图象校正过量或不足的问题。     

Topological optimization of continuum structures with design-dependent surface loading – Part II: algorithm and examples for 3D problems

The problem of topology optimization of 3D structures with design-dependent loading is considered. An algorithm for generating the valid loading surface of the 3D structure is presented, constituting an extension of the algorithm for 2D structures developed in Part I of this paper on the basis of a modified isoline technique. In this way the complicated calculation of the fit of the loading surface of a 3D structure may be avoided. Since the finite element mesh is fixed in the admissible 3D design domain during the period of topology evolution, the design-dependent loading surface may intersect the elements as the design changes. Independent interpolation functions are introduced along the loading surface so that the surface integral for generating the loading on the surface of the 3D structure can be performed more efficiently and simply. The bilinear 4-node serendipity surface element is constructed to describe the variable loading surface, and this matches well with the 8-node isoparametric 3D elements which have been used for the discretization of the 3D design domain. The validity of the algorithm is verified by numerical examples for 3D problems. Results of designing with design-dependent loads and with corresponding fixed loads are presented, and some important features of the computational results are discussed.