装载机后车架焊接顺序优化的数值仿真

利用热弹塑性有限元法和Marc对装载机后车架的焊接变形进行数值仿真.分别用壳单元和实体单元进行仿真,对比焊接角变形,结果表明两者精度比较相似.建立后车架壳单元热-力耦合模型,定性对比在相同约束条件下焊接顺序对整个后车架结构内缩变形和面外弯曲变形的影响.结果表明,在先焊接框架焊缝的条件下,整体结构刚度增大,各种变形较小;其中,当采用正/反面焊缝、立焊缝依次焊接时,大梁下挠峰值最小,为0.002 m,从而确定后车架最佳焊接顺序方案,在该顺序下的变形模拟值与实测值吻合良好.     

三维实体转子系统热-结构耦合响应分析

以某型航空发动机高压转子系统为研究对象,基于不均匀分布稳态温度场,建立了某高压转子系统三维实体单元有限元模型以及稳态温度场下转子系统热-结构耦合振动方程,利用热-结构-动力学耦合理论,采用间接耦合法,通过稳态温度场分析和静力分析生成热应力,然后进行预应力模态分析,最后利用模态叠加法进行不平衡量和热弯曲耦合响应分析,实现热-结构-动力学耦合计算.通过稳态温度场对典型级盘稳态响应影响的分析以及不平衡量与热弯曲耦合稳态响应分析,发现耦合响应对转子系统各级盘的振动响应有较大影响.     

熔盐堆临界能谱与通量分布的仿真计算

研究熔盐反应堆在临界工况下的堆芯中子能量和中子通量分布.由于熔盐反应堆的几何结构与目前的热中子反应堆存在很大差异,导致热中子反应堆能谱的求解方法在对熔盐堆进行计算时存在几何处理上的困难.针对上述问题,提出采用具有任意几何处理能力的中子输运计算软件MCNP对熔盐堆堆芯结构进行建模,采用能量区间上的平均通量代替该区间内通量分布的方法,计算了两种熔盐堆在临界工况下的堆芯中子能谱.结果表明,MSBR堆芯能谱为典型的热堆能谱;MO-SART堆芯能谱介于快堆能谱和热堆能谱之间.结果能够作为堆芯扩散计算中能量分群方法的依据.同时分析了堆芯内中子通量分布情况,结果表明熔盐堆中子通量分布具有中间高、四周低的特点.     

针穿刺软组织变形有限元仿真

为了提高机器人辅助针穿刺精度,提出一种对软组织变形分析的准静态有限元法.该方法基于针受力下软组织变形机理,将软组织变形的连续动态过程分解成离散的准静态过程;采用重叠单元法在ANSYS中建立了软组织变形的二维和三维准静态有限元模型,并进行了仿真实验.最后通过实验结果验证了该方法的有效性和可行性.     

基于有限元分析的建筑机械载荷仿真研究

选取ANSYS有限元软件采用整体式模型建模方法建立建筑模型，选取SOLID65单元建立模型砂浆与砌块部分，SOLID65单元可以模拟建筑墙体中钢筋混凝土的开裂、塑性形变等力学性能，实现建筑机械载荷的有效仿真。仿真结果表明，施加于墙体机械载荷大小为86.9 kN时，墙体出现开裂变形；施加于墙体机械载荷大小为115.7 kN时，墙体出现破坏坍塌情况。     

实体建模数值反应堆的高质量绘制

针对传统体绘制算法采用全局实体网格化和光线均匀采样策略,难以适应大规模数值反应堆数据的可视分析问题,提出一种面向实体特征的数值反应堆可视化方法.首先利用高重复性的组件特征设计按需网格化的绘制流水线,支撑网格高效重建;然后采用均质属性的实体特征,提出基于表面的非结构网格体绘制加速算法;最后耦合轮廓线等表意性绘制增强效果.实验结果表明,该方法能够可扩展地处理大规模反应堆数据,高质量地表现反应堆结构和关键介质界面.     

基于Abaqus的过盈装配有限元分析

针对某结构固定孔与套筒的过盈装配问题,利用Abaqus/Explicit建立该结构过盈装配的显式积分有限元分析模型.将固定孔视为可变形材料,采用八节点三维实体单元划分网格;将套筒定义为不变形的刚体结构,采用四节点离散刚体壳单元划分网格.通过对孔边应力分布情况的分析,说明计算结果与实际装配问题的一致性.最后对过盈装配中出现的偏心问题和采用壳单元建立有限元模型出现的问题进行讨论.     

风力发电机组圆柱齿轮的油温故障分析

为了提高风力发电机组齿轮箱工作的可靠性,研究了其油温高的故障特性.综合利用传热学、摩擦学和齿轮啮合理论,建立了圆柱齿轮传动三维热分析有限元模型.采用有限元法.计算在油温高故障状态下运转的圆柱传动齿轮温度分布、热变形和热应力.分析了双圆柱齿轮温度场和热变形的变化规律,并计算了齿轮频率和变形.求解结果显示出了风力发电机组齿轮箱在正常工作和故障频率情况下的形状、位移和等效应力的变化.该研究结果对其故障诊断具有一定的参考价值.     

正交切削加工过程仿真

为优化正交切削加工参数,采用弹-塑热耦合有限元方法,建立正交切削加工有限元模型.应用DEFORM软件,模拟出45号钢件切削过程中变形区内温度、应力、应变以及切削力的分布,采用自适应网格重划技术避免大塑性变形引起的网格畸变.该仿真结果能对切削加工参数的选择及实际的切削加工提供指导.     

三维有限元模型的任意剖切及其等值线与彩色云图生成的方法

对三维有限元模型快速有效地生成任意剖面上等值线及彩色云图,是有限元计算后处理中的一个重要技术。该文在建立单元信息描述表的基础上,提出了一种适合于任意三维实体单元类型的通用剖切算法,和在剖切面及外表面生成等值线或高质量彩色云图的方法。     

Effective stiffness and microscopic deformation of an orthotropic plate containing arbitrary holes

Many engineering materials and structures, such as cellular structures, sandwich core structures and laminated plates with holes, can be modeled by an inclusion problem with anisotropic matrix. The paper studies the effective properties and the microscopic deformation of anisotropic plates with periodic holes by using direct and mathematical homogenization. The effective stiffnesses are calculated by different homogenization methods and the microscopic deformation of a RVE is modeled by the finite element method for the plate with arbitrarily shaped holes. All of the effective stiffness coefficients, especially stretching-shear coupling coefficients are evaluated.     

基于SPH与FEM的结构入水分析方法

建立基于光滑粒子动力学（smoothed particle hydrodynamics, SPH）、有限元法（finite element method, FEM）和无反射边界耦合的结构入水分析方法,将无限水域利用无反射边界条件截断成有限水域,将有限水域分为流体变形大的SPH区域、流体变形小的FEM区域和声学流体FEM区域,结构用FEM离散。采用通用接触算法模拟SPH与FEM的耦合,采用声固耦合方法处理FEM区域之间的耦合,建立流固耦合的SPH FEM分析方法。该方法结合SPH模拟大变形的优点和FEM的高效性,可实现含自由液面变形、液体飞溅和无限水域等特点的流固耦合问题的模拟,为结构入水分析缩小离散区域、降低自由度和SPH粒子数等提供一种有效的分析方法。     

Finite element modeling of borehole heat exchanger systems: Part 1. Fundamentals

Single borehole heat exchanger (BHE) and arrays of BHE are modeled by using the finite element method. The first part of the paper derives the fundamental equations for BHE systems and their finite element representations, where the thermal exchange between the borehole components is modeled via thermal transfer relations. For this purpose improved relationships for thermal resistances and capacities of BHE are introduced. Pipe-to-grout thermal transfer possesses multiple grout points for double U-shape and single U-shape BHE to attain a more accurate modeling. The numerical solution of the final 3D problems is performed via a widely non-sequential (essentially non-iterative) coupling strategy for the BHE and porous medium discretization. Four types of vertical BHE are supported: double U-shape (2U) pipe, single U-shape (1U) pipe, coaxial pipe with annular (CXA) and centred (CXC) inlet. Two computational strategies are used: (1) The analytical BHE method based on Eskilson and Claesson's (1988) solution, (2) numerical BHE method based on Al-Khoury et al.'s (2005) solution. The second part of the paper focusses on BHE meshing aspects, the validation of BHE solutions and practical applications for borehole thermal energy store systems.     

基于有限元方法的心脏表面建模

利用有限元与生物力学原理构建心脏表面运动的有限元方程,快速建立四面体网格的有限元心脏模型,模拟心脏的动态形变,从心脏的三维表面恢复、应力应变分析和三维运动建模等方面着手,分析计算心脏在收缩期相邻时刻的应力分布及形变情况,有效地模拟了心脏的动态形变。实验结果表明了该方法的有效性和可行性。     

Effect of thermal deformations of an optical pick-up base on the optical properties of DVD optical system

An analytical method is presented to analyze the effect of thermal deformations of an optical pick-up base on the optical properties of DVD optical system. To measure the amount of thermal deformations of an optical pick-up base, finite element analysis and holographic interferometry were used. First, thermal deformations of an aluminum pick-up base was analyzed in thermal environments using finite element analysis; finite element analysis was carried out without the initial surface stress condition. The measurement of thermal deformations by holographic interferometry was carried out to verify finite element analysis results. However, since the finite element analysis results were deviated from those by experiment, the effect of the initial surface stress condition was considered; finite element analysis was carried out with the initial surface residual stress condition, which was obtained from X-ray diffraction measurement. The finite element analysis results with the initial surface stress condition agreed well with the experimental results by holographic interferometry. Finally, to analyze the effect of thermal deformations of the pick-up base on the optical properties of DVD optical system, the deformation of optical path was analyzed. However, the drastic changes of beam spot, beam intensity profile, modulation transfer function curve and wavefront aberration were not observed.     

Three dimensional finite element modeling of thermomechanical frictional contact between finite deformation bodies using R-minimum strategy

An algorithm for analyzing the transient thermal coupling with the frictional contact between the multiple elastic–plastic bodies in finite deformation is presented using the R-minimum strategy. An arbitrarily shaped contact element strategy, named as node-to-point contact element strategy, is proposed to handle the thermomechanical frictional contact between finite deformation bodies. Assuming the material properties to be temperature dependent, the constitutive equations for both the thermomechanical frictional contact and the thermal-elastic–plastic materials are deduced respectively and applied in our finite element code. Finally, two examples are presented to show the efficiency and usefulness of this algorithm.     

离散元-有限差分跨尺度耦合下桩与土体稳定性细观数值分析

为准确分析桩体宏观变形与周围土颗粒细观力学行为,采用离散元-有限差分的跨尺度耦合进行桩和土体接触过程中的稳定性分析,研究桩下沉过程中周围土体的细观变形、应力分布和桩体自身变化情况,通过FLAC3D建立桩和外部土体有限差分网格单元,对桩周围侧土体应用PFC3D离散元建立土颗粒微观结构模型.研究结果表明:离散元与有限差分耦合方案能够模拟桩周围土体细观力学行为;外部区域土体位移场呈包裹式C形对称分布,应力场以竖直应力为主导,离散元土颗粒接触力链网格以树根状向周围递减削弱分布;桩弹性单元体下沉时,应力场和位移场均有分层现象,应力场以压应力为主,但存在局部拉应力即反弹现象.     

A nodal analysis model for the out-of-plane beamshape electrothermal microactuator

This paper introduces a nodal analysis model for the out-of-plane beamshaped electrothermal microactuators. The electrothermal microactuator is traditionally simulated with finite element method (FEM) due to the complex coupling of the electrical, thermal and mechanical problem. This complex problem is classified into two parts in this paper: the coupling electrothermal problem and the coupling thermomechanical problem. By utilizing the characteristic of the temperature distribution, the nodal analysis model for the coupling electrothermal behavior of the electrothermal microactuator is built. The model scale is much smaller than the finite element model, which results in less computational consumption. Then the coupling thermomechanical behavior, such as the shift of the heat flow from the bottom of each part of the actuator to the substrate due to its out-of-plane movement, is modeled to make the model more reasonable. Many other effects which remarkably influence the behavior of the actuator are also taken into account. This model is verified by available experimental results, and achieves an agreement.     

Finite element formulation for dynamics of planar flexible multi-beam system

In some previous geometric nonlinear finite element formulations, due to the use of axial displacement, the contribution of all the elements lying between the reference node of zero axial displacement and the element to the foreshortening effect should be taken into account. In this paper, a finite element formulation is proposed based on geometric nonlinear elastic theory and finite element technique. The coupling deformation terms of an arbitrary point only relate to the nodal coordinates of the element at which the point is located. Based on Hamilton principle, dynamic equations of elastic beams undergoing large overall motions are derived. To investigate the effect of coupling deformation terms on system dynamic characters and reduce the dynamic equations, a complete dynamic model and three reduced models of hub-beam are prospected. When the Cartesian deformation coordinates are adopted, the results indicate that the terms related to the coupling deformation in the inertia forces of dynamic equations have small effect on system dynamic behavior and may be neglected, whereas the terms related to coupling deformation in the elastic forces are important for system dynamic behavior and should be considered in dynamic equation. Numerical examples of the rotating beam and flexible beam system are carried out to demonstrate the accuracy and validity of this dynamic model. Furthermore, it is shown that a small number of finite elements are needed to obtain a stable solution using the present coupling finite element formulation.