有旋转自由度的高精度三角形单元

本文从三次平面等参元出发，构造出角结点有旋转自由度的三角形单元。该单元与三次平面等参元有相同的单元特征及精度，同时具有连续介质力学中关于旋转度的定义。     

有旋转自由度的高精度四边形单元

从具有三次位移模式的平面等参元出发 ,通过对单元自由度进行线性变换并引入连续介质力学中关于旋转度的定义 ,构造出角结点有旋转自由度的高精度四边形单元。该单元与平面等参元有相同的单元特征及精度     

带旋转自由度C^0类任意四边形板（壳）单元

基于Ｒｅｉｓｓｎｅｒ－Ｍｉｎｄｉｌｉｎ板弯曲理论和Ｖｏｎ－Ｋａｒｍａｎ大挠度理论,采用单元域内和边界位移插值一致性的概念,将四节点等参弯曲单元与Ａｌｌｍａｎ膜变形二次插值模式相结合,对层合板壳的大挠度分析提供了一种实用的带旋转自由度的四节点Ｃ＾０类板单元。大量算例表明：该单元对板壳结构的线性强度、稳定性和后屈曲分析都表现出良好的收敛性和足够的工程精度。     

带旋转自由度的精化非协调平面四边形等参元

对于C~1类不协调元文[1]提出了一种精比直接刚度法。本文进一步将其应用到C~0类问题,建立一种带旋转自由度的不协调平面四边形单元,其协调部分是用人Allman插值法建立的单元函数,不协调部分用了四个内部自由度。该单元能保证通过分片试验,保持了单变量有限元列式简单、性能可靠(无多余零能模式及坐标不变性)等长处,同时,还具备多变量有限元(杂交/拟协调元)高精度的优点。算例表明,本文提出的单元收敛、可靠、高精度且高效率。     

框架一剪力墙结构分析的高精度平面单元

从三次平面等参元出发，构造出欠妥结点有旋转自由度的高精度矩形单元，该单元与平面等参元具有相同的单元特征及精度，同时具有连续介质力学中关于旋转度的定义。     

一种有效的厚薄板壳单元

对于厚薄板壳分析提出了一种有效的拟协调位移型三角型单元。采用Ｍｉｎｄｌｉｎ变形假定，在横向剪切刚度项中引入特殊的罚函数，有效地解除了剪切闭锁和抑制了零能模式，并扩大了对跨厚比的适用范围，计算精度也明显提高。文中给出了各种材料和形状板壳的线性和非线性分析。     

基于解析试函数三角形带旋转自由度膜元的显式格式研究

三角形单元是有限元分析中常用的单元.在平面单元内引入结点转动自由度,可以提高单元位移场的阶次,在不增加单元结点的前提下提高单元性能.论文利用问题基本解析解作为试函数来构造带旋转自由度的三角形单元ATF-R3H,采用了杂交应力函数单元模式,确保了单元优良的抗畸变性能和较高应力计算精度.论文利用直角坐标与三角形面积坐标的线性关系,以及面积坐标幂函数在三角形域内和边界上的积分公式,直接给出单元刚度矩阵的显式表达式,从而避免了大量数值积分,提高了计算效率.数值算例表明,显式格式的ATF-R3H单元具有良好的性能.     

钢柱抗爆响应分析单自由度模型适用性评估

为评估单自由度(SDOF)模型在结构抗爆设计中的适用性,分别采用SDOF模型和通用有限元软件ANSYS/LS-DYNA对简支钢柱承受爆炸荷载时的动力响应进行模拟;对比二者计算结果,并以有限元模拟为准,分析SDOF模型的适用范围。研究表明:可按照自由振动阶段SDOF模型位移结果的振幅大小,将其位移响应划分为有限变形阶段、临界阶段、失稳破坏阶段,有限变形阶段SDOF模型与有限元结果基本一致;截面高宽比、翼缘宽厚比对钢柱动力破坏形式有重要影响,高宽比越大、翼缘的宽厚比越小,越容易发生平面外弯扭失稳;在SDOF模型中通过假定塑性铰分布长度计算塑性阶段应变及应变率,采用随时间变化的应变率计算Cowper-Symonds本构关系中的应力放大系数是可行的。     

大学物理《力学》中的自由度分析

对《力学》中的物体自由度进行多方面分析,以深化教学、提高学生正 确分析物理问题的能力.使用实际教学分析的研究方法,在《力学》范围内讨论自由度与坐标、 自由与约束的关系并得以下结论: (1) 同一物体的自由度随其所在的``空间'不同而不同, 不因坐标系的选取不同而 异, 在同类参考系中不因参考系的动静而有别;(2)自由度遵循叠加原理. 讨论了质点系的总自由度及相关计算问题,并指出研究《力学》中自由度的意义.     

薄膜横向振动的有限元分析

构造了一种3节点三角形膜单元,以适用于平面薄膜横向振动的有限元分析.在给出单元形函数的基础上,根据最小势能原理建立了薄膜自由振动方程,并推导了单元刚度矩阵和单元质量矩阵.研究结果表明,单元刚度矩阵和单元质量矩阵形式简单,且自由度少;通过两个典型算例,证明3节点三角形膜单元的计算结果非常接近理论解,同时可以达到很高的精度...     

A meshfree-based local Galerkin method with condensation of degree of freedom for elastic dynamic analysis简

Condensation technique of degree of freedom is first proposed to improve the computational efficiency of meshfree method with Galerkin weak form for elastic dy- namic analysis. In the present method, scattered nodes with- out connectivity are divided into several subsets by cells with arbitrary shape. Local discrete equation is established over each cell by using moving Kriging interpolation, in which the nodes that located in the cell are used for approxima- tion. Then local discrete equations can be simplified by con- densation of degree of freedom, which transfers equations of inner nodes to equations of boundary nodes based on cells. The global dynamic system equations are obtained by as- sembling all local discrete equations and are solved by using the standard implicit Newmark＇s time integration scheme. In the scheme of present method, the calculation of each cell is carried out by meshfree method, and local search is imple- mented in interpolation. Numerical examples show that the present method has high computational efficiency and good accuracy in solving elastic dynamic problems.     

A simple and efficient triangular finite element for plate bending

A simple and efficient triangular finite element is introduced for plate bending application. The element is a three-node triangular one with three basic degrees of freedom per node and two internal rotation degrees of freedom, using selective reduced integration. Numerical examples indicate that, despite its simplicity, the element is not only competitively accurate, but also useful as a thick/thin triangular plate bending element. It is also pointed out that this element using selective reduced integration is in fact a mixed element.     

自由度对鱼类自主游动数值模拟结果的影响

采用自适应浸没边界方法,数值模拟了仿生鱼在不同自由度个数情况下的游动,对比分析了自由度个数对仿生鱼受力、能耗、推进效率以及尾涡结构的影响。研究结果表明,推进效率随着自由度个数的增加而略有降低;当仿生鱼在自主游动过程中没有侧向运动速度时,侧向受力幅值会大幅度提高。另外,当采用"六自由度模型"进行模拟时,仿生鱼很难沿直线运动,从而导致定量分析的困难。     

Finite element study of free surface turbulent flow in rotating channels

Under certain conditions of liquid flow through rotating channels, the Coriolis force can induce a free surface to be formed. This problem is of practical importance in a Coriolis wear tester, which is used for determining the sliding wear coefficient of wear materials in slurry handling equipment. A deforming Galerkin finite element method is presented for predicting two‐dimensional turbulent free surface mean flow in rotating channels. Reynolds‐averaged Navier–Stokes (RANS) equations are cast into weak(algebraic) form using primitive variables (velocity and pressure). Eddy viscosity is determined via a mixing length model. Velocity is interpolated biquadratically, while pressure is interpolated bilinearly. The kinematic condition is used to form the Galerkin residual for the free surface. The free surface is represented by Hermite polynomials of zeroeth order for continuity of position and slope. Combined Newton's iteration is used to simultaneously solve for the free surface and the field variables. Results of velocity and pressure fields, as well as the free surface are shown to converge with mesh‐size refinement. There is excellent respect for mass conservation. Results are presented for various values of Rossby number (Ro) and height‐based Reynolds number (Re_H). Parameter continuation in Ro and Re_H space is used to compute solutions at higher values of flow rate and angular velocity. Copyright © 2002 John Wiley & Sons, Ltd.     

旋转三角形绳系卫星编队系统动态稳定性分析

本文研究了平动点附近的旋转三角形绳系卫星编队系统的动态稳定性问题.为了便于分析,假设系绳始终保持张紧状态,且不计系绳的质量.为了建立更加符合实际的数学模型,考虑了姿态运动和轨道运动的相互影响,即姿轨耦合,并在此基础上推导出了考虑姿轨耦合的非线性动力学方程.最后用数值方法模拟了在不同的旋转速度情况下系统的动态稳定性,模拟结果表明旋转速率越大系统稳定性越好.