Sintering zone prediction in direct metal laser sintering by finite element method

A three-dimensional finite element thermal model in direct metal laser sintering(DMLS) including the effect of powder-to-solid transition were established to predict sintering zone, which benefited the determination of suitable process parameters in DMLS. The nonlinear transient model of the metals thermal conductivity for powder-to-solid transition was developed. The model uses solid thermal properties of material in liquid-phase zone, transitional ones in sintering or sintered zone and powder ones in unsintered zones of powder bed to predict, respectively. Sintering zone boundary was estimated by maximum temperature history profile. Experiments were carried out using multi-component Cu-based metal powder. Compared experimental and predicted results, the mean error of sintering depth and width are 7.8% and 14.4%, respectively, which confirms the accuracy of the FEM prediction.

Multiple linear system techniques for 3D finite element method modeling of direct current resistivity

The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and stored in two parts separately. One part is associated with the volume integral and the other is associated with the subsurface boundary integral. The equivalent multiple linear systems with closer right-hand sides than the original systems were constructed. A recycling Krylov subspace technique was employed to solve the multiple linear systems. The solution of the seed system was used as an initial guess for the subsequent systems. The results of two numerical experiments show that the improved algorithm reduces the iterations and CPU time by almost 50%, compared with the classical preconditioned conjugate gradient method.

Finite element model updating of a rod-type ultrasonicmotor based on response surface method

The conventional finite element model （FEM） of a rod-type ultrasonic motor is usually simplified by means of continuous composite structure. Because the actual contact characteristics between the parts of the ultrasonic motor is ignored, there is bigger error between the calculated values and experimental results. Aiming at solving problem, a new modeling method of a rod-type ultrasonic motor is presented to obtain a high-accuracy FEM. The bolt pretension and the normal contact stiffness and friction coefficient of the contact surface of ultrasonic motor are all considered in this method, and the significant parameters of working mode of the motor are selected by the response surface method, and the goal of calculating the structural response rapidly is realized by building the response surface model to replace the FEM. The result of finite element model updating shows that the average error of modal frequencies of updated model drops to 0.21% from 1.20%. The accuracy of FEM is obviously improved, which indicates that the FEM updating based on response surface method is of great application value on the design for a rod-type ultrasonic motor.

h-P Finite Element Approximation for Full-Potential Electronic Structure Calculations

The(continuous) finite element approximations of different orders for the computation of the solution to electronic structures were proposed in some papers and the performance of these approaches is becoming appreciable and is now well understood.In this publication,the author proposes to extend this discretization for full-potential electronic structure calculations by combining the refinement of the finite element mesh,where the solution is most singular with the increase of the degree of the polynomial approximations in the regions where the solution is mostly regular.This combination of increase of approximation properties,done in an a priori or a posteriori manner,is well-known to generally produce an optimal exponential type convergence rate with respect to the number of degrees of freedom even when the solution is singular.The analysis performed here sustains this property in the case of Hartree-Fock and Kohn-Sham problems.

7N01铝合金Johnson-Cook模型参数的反算方法

对动车组用7N01铝合金进行准静态单向拉伸试验,获取应力-应变曲线。采用曲线拟合和有限元仿真优化相结合的方法反算铝合金Johnson-Cook模型参数:通过曲线拟合方法确定模型初始参数,将其代入有限元模型,应用HyperStudy软件实现与有限元模型及求解器的数据传递与过程集成,采用遗传算法和自适应响应面法对材料参数进行优化,并将优化后的有限元仿真结果与拉伸试验结果进行对比。结果表明:利用遗传算法和自适应响应面法反算材料参数,优化收敛速度快,仿真数据与试验数据吻合度高,2种方法均可以用来进行参数反算的优化。

Method of determining grid sizes of finite element method of water quality models for geometrically complex river course

The method of determining grid sizes of finite element method of water quality models is presented on the basis of characteristics of pollutant distributed in the just downstream grid of discharge. A given length of the grid is applied to calculate the minimum distance for the pollutant to complete mixing in the lateral direction in the just downstream grid of the discharge, and the minimum distance is regarded as the maximum width of the grid. Application of the maximum width of the grid and flow rate per unit width of the river results in the number of flow zones in the lateral direction of the river. Consequently division of grids and numerical calculation of water quality with finite element method can be carried out on the basis of available method and topographic map of the river course. Analysis of sensitivity shows that the effect of the width of the river and the effect of the length of the grids on the minimum number of flow zones in the lateral direction is relatively small, and that the effect of the given lateral mixing degree of the pollutants on the minimum number of flow zones is acceptable, which indicates that the method presented is relatively stable. The method can avoid the blindness and randomness in determining the number of flow zones, and can decrease the amount of computation under the condition that the accuracy requirement is met. The problem that determining the sizes of the grids must rely on empirical knowledge has been solved.

基础激励下裂纹梁结构疲劳寿命预测模型

为了发展基于模型的裂纹梁结构疲劳寿命预测方法,提出了一种新的三维裂纹梁单元刚度矩阵。基于该刚度矩阵,建立基础激励下裂纹梁结构的三维有限元模型。推导三维裂纹梁单元的应力强度因子,建立三维裂纹梁单元的疲劳裂纹扩展模型。采用振动响应与裂纹扩展增量交互计算方法,计算循环载荷作用下裂纹梁结构的疲劳寿命。研究结果表明:裂纹梁结构寿命预测模型较好地体现了疲劳裂纹扩展寿命与基础激励参数、结构参数和裂纹参数之间的内在关系,反映了基础激励对裂纹梁结构疲劳寿命的影响。最后通过实验对模型进行了验证。

输电塔钢管角钢组合节点承载能力模拟分析与计算方法研究

依托输电线路实际工程,选取输电铁塔主材与横担连接处钢管角钢组合节点为研究对象,采用数值软件ABAQUS建立了钢管角钢组合节点精细化有限元模型,并通过静力加载试验验证了有限元模型的合理性;随后模拟分析了组合节点的传力机理和应力分布,明确了不同参数对组合节点受力特性的影响规律。结果表明,钢管、中环板与竖向板相交区域出现应力集中且最大应力达到屈服强度,并向四周扩散且逐渐减小,中环板和竖向板的厚度是影响组合节点极限承载力的关键因素。采用有效宽度法计算了中环板和竖向板的承载能力,建立了不同板件的内力占比计算式,基于此,提出了组合节点承载力计算方法。所提出的极限承载力计算方法与数值模拟结果的误差在13%以内,验证了计算方法的合理性,可为钢管角钢组合节点的结构设计与分析提供参考。

基于SBFEM的剪切型裂纹动态开裂模拟

剪切型断裂是岩土工程中常见的破坏模式,了解剪切破坏机理并准确预测剪切型裂纹的萌生、扩展过程对保障工程结构的安全性与稳定性具有重要意义.文章建立了基于比例边界有限元法(scaled boundary finite element methods,SBFEM)和非局部宏-微观损伤模型的剪切型裂纹动态开裂模拟方法,定义了基于偏应变概念的物质点对的正伸长量,可作为预测剪切型裂纹扩展行为的动态开裂准则,一点的损伤定义为该点影响域范围内连接的物质键损伤的加权平均值,而物质键的损伤则与基于偏应变概念的物质点对的正伸长量相关联,并引入能量退化函数建立结构域几何拓扑损伤与能量损失之间的关系,将拓扑损伤与应力应变联系起来,通过能量退化函数修正了SBFEM的刚度系数矩阵,得到了子域在损伤状态下的刚度矩阵,推导了考虑结构损伤的SBFEM动力控制方程,采用Newmark隐式算法对控制方程进行时间离散.最后,通过3个典型算例验证了建议的模型可较好地模拟剪切型断裂问题,能够很好地捕捉剪切型裂纹的扩展路径,并得到较为准确的载荷-位移曲线.

计及IGBT模块键合线与芯片焊料层老化的热网络法结温计算

文中提出一种计及IGBT模块键合线与芯片焊料层老化的热网络法结温计算,基于Simulink对短时间尺度下损耗与结温的相互依赖关系进行更新,并分别通过双脉冲测试及有限元仿真修正长时间尺度下键合线与芯片焊料层老化对IGBT结温计算的影响,在此基础上,根据芯片焊料层不同老化状态下键合线的应力特征,实现两种老化模式的相互关联,较为准确地计算IGBT结温。最终利用试验平台与传统结温计算方法进行对比验证了所提结温计算方法的准确性。该结温计算方法有助于在实际运行工况及IGBT模块老化状态下精确计算结温。

大型梁式承台模型试验及跨中挠度简化计算方法研究

为了解大型梁式承台的力学性能,以某快速化改造工程的大型梁式承台为背景,按照缩尺比1∶10制作梁式承台模型进行力学性能试验,结合有限元计算,分析梁式承台结构受力、破坏模式、开裂情况等,并研究不同跨高比条件下梁式承台的受力特性。结果表明:在跨中荷载作用下,梁式承台受力大致可以分为线弹性阶段、裂缝发展阶段和屈服阶段3个阶段;线弹性阶段截面应力分布已不满足平截面假定,剪切效应对结构变形的影响不可忽略;模型最终破坏模式为弯曲破坏;裂缝主要表现为跨中弯曲裂缝和斜裂缝;跨高比越小,梁式承台剪切刚度越大。为考虑剪切效应对梁式承台变形的影响,拟合得出梁式承台跨中挠度的简化计算方法,将该方法计算值及规范计算值与试验值进行对比,可得在裂缝发展阶段,规范计算值与试验值偏差较大,所提方法计算值与试验值偏差较小,该方法可用于线弹性阶段及裂缝发展阶段梁式承台跨中挠度的初步估算。

基于直接多层有限元模拟的二维压电材料的力电性能研究

该文采用直接多层有限元模拟(Direct multi-layer finite element,Direct FE^(2))方法,模拟非均质材料的力-电耦合问题。该方法突破了传统并发多尺度分析方法必须依赖控制脚本进行宏-微观跨尺度信息传递的固有框架。首先,通过有限元的控制方程和并发多尺度分析所需的Hill-Mandel均质化条件,推导出可直接实现宏观与微观信息实时传递的多节点约束方程。其次,将并发多尺度分析所需的宏观结构模型和代表体积单元模型合并为一个有限元模型,避免了在两个尺度之间的重复数据传输。最后,通过算例验证该文算法的正确性和有效性。

基于等效线性化隔震结构设计周期折减系数研究

《建筑隔震设计标准》提出的隔震设计是基于复振型分解反应谱等效线性化的一体化直接设计方法,但未提及隔震结构周期折减系数如何取值。基于此,根据刚度串联关系推导等效单自由度隔震体系周期折减系数简化计算公式,探讨隔震结构周期折减系数因素的影响规律,建立不同填充材料、不同填充率的有限元数值模型,并利用数值模拟结果验证隔震结构周期折减系数简化计算公式。结果表明:隔震结构周期折减系数与名义周期比、非隔震结构周期折减系数存在函数关系;墙体开洞与通高墙体的隔震结构的周期折减系数均随着填充率的增大而减小,当填充率相同时,呈现出随填充材料弹性模量增大而减小的趋势,墙体开洞会增大隔震结构周期折减系数,且隔震结构的周期折减系数的取值范围相对较窄,为0.915~0.965;数值有限元模拟与理论结果偏差小于3%,吻合度高,以验证隔震结构周期折减系数简化计算公式的正确性,说明该简化计算方法对隔震工程设计具有一定指导意义。

Modeling and Analysis of Spoke-Type Permanent Magnet Vernier Machine Based on Equivalent Magnetic Network Method

In this paper,a new equivalent magnetic network(EMN)model is established for a spoke-type permanent magnet(PM)vernier(PMV)machine.Two different modeling methods are proposed for different parts of the PMV machine,considering that their magnetic field distributions are quite different.Hierarchical modeling method is proposed for the modeling of the rotor as the magnetic intensity of the rotor iron core presents gradient distribution along the radial direction.Mesh based reluctance network method is used for the modeling of flux modulation poles with irregular and unstable magnetic field distributions.Moreover,accurate PM leakage permeance calculation formulae are deduced to improve the simulation precision.The electromagnetic parameters,such as flux linkage,back electromagnetic force,electromagnetic torque and iron loss are predicted by the proposed EMN model.Finally,finite element analysis(FEA)and experimental results are given to verify the effectiveness of the proposed methods.

基于矩独立法的异质叠层复合材料铆接工艺参数灵敏度分析研究

为解决碳纤维增强复合材料(Carbon fber reinforced polymer,CFRP)与金属材料叠层构件铆接工艺复杂化的问题,提出了一种基于矩独立方法的叠层复合材料铆接工艺参数灵敏度分析的方法。首先,以CFRP与铝合金(Al)异质叠层材料结构为研究对象,采用有限元方法建立了CFRP/Al叠层结构的铆接仿真分析模型,并通过试验验证了仿真分析模型的正确性。其次,以铆接干涉量为目标,建立了基于随机森林方法的铆接工艺参数代理模型;随后通过代理模型进行数据扩展,以17项铆接工艺参数为输入变量,铆接干涉量为输出变量,采用基于矩独立的PAWN方法进行全局灵敏度分析,并给出了基于该方法的灵敏度系数。在铆接工艺参数对铆接干涉量的全局灵敏度系数中,异质叠层复合材料的弹性模量和厚度的灵敏度系数较大,分别为0.16921和0.11837,其次是系数为0.012的位移载荷和0.011的铆钉直径。其余工艺参数的灵敏度系数较小,一些对铆接干涉量影响很不显著的参数的灵敏度系数接近0。

基于有限元分析法的双基础立式泵机组减振的研究与改造

采用有限元分析法,基于大型有限元软件ANSYS建立机组与楼板的模型,对大型双基础立式泵机组的振动和电机层楼板的承载能力进行分析评估。旨在经过不断修正获取动力特性与实测值较为吻合的结构有限元模型。通过实践改造,有效降低楼板振动,提高泵站运行的安全可靠性。

基于同一车体结构模型的不同优化算法对比研究

高速列车工程优化设计中有多种优化算法,解决实际优化问题时选择合适的算法能提高优化设计效率。以某一高速列车铝合金车体为模型,通过有限元分析计算整备状态下的车体一阶垂弯频率较低。在灵敏度分析的基础上,应用正交试验对各个变量进行主效应分析,筛选出主要变量作为优化模型的设计变量。以提高一阶垂弯频率为目的,基于近似模型分别采用可行方向法和遗传算法进行优化求解,使用可行方向法优化后的车体一阶垂弯振动频率提升2.4%,二阶菱形振动提升1.9%,车体钢结构质量增重0.15%;使用遗传算法优化后车体一阶垂弯振动频率提高了4.2%,车体的二阶菱形振动频率提高2.5%,车体钢结构质量增重1.66%。对优化结果进行对比分析,两种不同算法的优化结果侧重点有所不同,可根据不同实际需求选择相应的优化算法,从而达到优化目的。

筒型基础防波堤稳定性简化计算方法

筒型基础防波堤是一种新型港口与海岸工程结构,依靠下部筒体沉入土中维持结构稳定。结合实际工程,建立了筒型基础防波堤稳定性分析的三维弹塑性有限元模型,得出了其失稳模式为绕基础筒底以下某点发生转动失稳。通过对结构进行极限状态受力分析,建立了基于实际转动点的结构稳定性计算方法,对稳定性计算模型和土体作用力计算公式等进行了检验。在此基础上,将转动点移至基础筒底部距结构中心线水平距离为h′的位置,以此作为结构倾覆破坏时的假想支撑点,建立了基于重力式结构稳定性验算模式的筒型基础防波堤稳定性分析的简化方法。通过不同基础尺度下计算结果的分析比较,建议了h′的取值。与有限元计算结果的比较表明,建立的简化计算方法具有较高的精度,可供实际工程参用。

筒型基础防波堤土压力性状的有限元分析

筒型基础防波堤是一种新型港口与海岸工程结构,依靠沉入地基土层中的筒型基础维持结构稳定,作用在筒型基础上的土压力是结构稳定性验算的核心内容。结合某实际工程,建立了筒型基础防波堤三维弹塑性有限元模型,分析了不同波浪力加载值下作用在筒型基础上土压力的大小及竖向和环向分布规律,并将有限元计算的极限状态下的土压力与Rankine主动、被动土压力和静止土压力进行了比较分析。根据筒型基础的位移模式,将土压力分为主动、被动和静止3个区域,建议了不同区域土压力的简化计算方法,为筒型基础结构稳定性验算提供了基本依据。

穿浪双体船横向强度与扭转强度的有限元计算

穿浪双体船的连接桥在横浪和斜浪中遭受比较大的横向弯矩和扭转力矩的作用,其自身的强度对穿浪双体船的安全性来说至关重要。本文在有限元理论的基础上,采用直接计算方法对一艘穿浪双体船进行了横向强度和扭转强度的整船有限元分析,对其总强度进行了校核,并初步分析了该船上层建筑对总横强度的影响。通过对计算结果的分析,掌握了该船的应力分布,为结构优化设计提供依据。