Study on Contact Algorithm of Dynamic Explicit FEM for Sheet Forming Simulation

Based on existing algorithms, a newly developed contact search algorithm is proposed. The new algorithm consists of global search, local searching, local tracking and penetration calculation processes. It requires no iteration steps. It can deal with not only general tool surfaces with vertical walls, but also tool surfaces meshed with elements having very poor aspect ratios. It is demonstrated that the FE code employing this new contact search algorithm becomes more reliable, efficient and accurate for sheet metal forming simulation than conventional ones.

Analysis of composite material interface crack face contact and friction effects using a new node-pairs contact algorithm

A new node-pairs contact algorithm is proposed to deal with a composite material or bi-material interface crack face contact and friction problem （e.g., resistant coating and thermal barrier coatings） subjected to complicated load conditions. To decrease the calculation scale and calculation errors, the local Lagrange multipliers are solved only on a pair of contact nodes using the Jacobi iteration method, and the constraint modification of the tangential multipliers are required. After the calculation of the present node-pairs Lagrange multiplier, it is turned to next contact node-pairs until all node-pairs have finished. Compared with an ordinary contact algorithm, the new local node-pairs contact algorithm is allowed a more precise element on the contact face without the stiffness matrix singularity. The stress intensity factors （SIFs） and the contact region of an infinite plate central crack are calculated and show good agreement with those in the literature. The contact zone near the crack tip as well as its influence on singularity of stress fields are studied. Furthermore, the frictional contacts are also considered and found to have a significant influence on the SIFs. The normalized mode-II stress intensity factors KII for the friction coefficient decrease by 16% when f changes from 1 to 0.

A hybrid contact approach for modeling soil-structure interaction using the material point method

The grid-based multi-velocity field technique has become increasingly popular for simulating the Material Point Method(MPM)in contact problems.However,this traditional technique has some shortcomings,such as(1)early contact and contact penetration can occur when the contact conditions are unsuitable,and(2)the method is not available for contact problems involving rigid-nonrigid materials,which can cause numerical instability.This study presents a new hybrid contact approach for the MPM to address these limitations to simulate the soil and structure interactions.The approach combines the advantages of point-point and point-segment contacts to implement contact detection,satisfying the impenetrability condition and smoothing the corner contact problem.The proposed approach is first validated through a disk test on an inclined slope.Then,several typical cases,such as granular collapse,bearing capacity,and deformation of a flexible retaining wall,are simulated to demonstrate the robustness of the proposed approach compared with FEM or analytical solutions.Finally,the proposed method is used to simulate the impact of sand flow on a deformable structure.The results show that the proposed contact approach can well describe the phenomenon of soil-structure interaction problems.

A GPU-Based Parallel Algorithm for 2D Large Deformation Contact Problems Using the Finite Particle Method

Large deformation contact problems generally involve highly nonlinear behaviors,which are very time-consuming and may lead to convergence issues.The finite particle method(FPM)effectively separates pure deformation from total motion in large deformation problems.In addition,the decoupled procedures of the FPM make it suitable for parallel computing,which may provide an approach to solve time-consuming issues.In this study,a graphics processing unit(GPU)-based parallel algorithm is proposed for two-dimensional large deformation contact problems.The fundamentals of the FPM for planar solids are first briefly introduced,including the equations of motion of particles and the internal forces of quadrilateral elements.Subsequently,a linked-list data structure suitable for parallel processing is built,and parallel global and local search algorithms are presented for contact detection.The contact forces are then derived and directly exerted on particles.The proposed method is implemented with main solution procedures executed in parallel on a GPU.Two verification problems comprising large deformation frictional contacts are presented,and the accuracy of the proposed algorithm is validated.Furthermore,the algorithm’s performance is investigated via a large-scale contact problem,and the maximum speedups of total computational time and contact calculation reach 28.5 and 77.4,respectively,relative to commercial finite element software Abaqus/Explicit running on a single-core central processing unit(CPU).The contact calculation time percentage of the total calculation time is only 18%with the FPM,much smaller than that(50%)with Abaqus/Explicit,demonstrating the efficiency of the proposed method.

CONTACT ALGORITHMS FOR CONTACT DYNAMICAL SYSTEMS

In this paper, we develop a general way to construct contact algorithms for contact dynamical systems. Such an algorithm requires the corresponding step transition map preserve the contact structure of the underlying contact phase space. The constructions are based on the correspondence between the contact geometry of R2n+1 and the conic symplectic one of R2n+2 and therefore, the algorithms are derived naturally from the symplectic algorithms of Hamiltonian systems.

AN IMPROVED CONTACT-IMPACT ALGORITHM FOR EXPLICIT INTEGRATION FEM

Although the penalty algorithm is simple and direct in concept, it has a defect that the contact forces are badly dependent on the chosen penalty factor. An improved contact-impact algorithm for the explicit integration FEM is proposed in the present paper. Based on the fact that bodies cannot penetrate into each other on the contact faces, a set of equations with the additional unknown contact forces on the slave nodes can be formed in a new system configuration. By solving these equations, the correct contact forces could be obtained without using the penalty factor.

A FINITE ELEMENT PARALLEL ALGORITHM OF THE PARAMETRIC VARIATIONAL PRINCIPLE FOR ELASTIC CONTACT PROBLEMS

Basetl on the finite element solution of the parametric varialional principle of elastic con/del problem, a corresponding parallel algorithm has been created bv utilizing the specialities of parallel computer and the architecture of concurrent processing in this paper. In this algorithm. the parallelisms have heen realized in the processes of creation and assembly of stiffness matrix, of the static condensation, of the solution of stresses and in many other aspects. The programme of this algorithm has been realized on ELXSI-6400 parallel computer of Xi'an Jiaotong University. The results of computation show that the computational time can be saved efficiently and it is an effective parallel algorithm for the analyses of contact problems.

A Genetic Algorithm for Simultaneous Determination of Thin Films Thermal Transport Properties and Contact Resistance

一个基因算法(GA ) 被学习同时决定热运输性质和在厚底层上扔的薄电影的接触抵抗。Apulsed 相片热反射(PPR ) 系统为大小被采用。GA 被用来提取热性质。大小在硅底层上在不同厚度的 SiO_2 薄电影上被执行。结果证明伴有 PPR 系统的 GA 为底层上的薄电影的热性质的同时的决心是有用的。

光滑粒子法中的摩擦接触算法及其在含界面土体变形问题中的应用

光滑粒子流体动力学(smoothed particle hydrodynamics,简称SPH)方法作为拉格朗日型的无网格粒子类方法,在固体极大变形问题的数值求解分析中具有显著优势。针对包含界面接触的固体大变形问题的SPH模拟,基于一种能改善边界精度的光滑粒子插值格式——有限粒子法(finiteparticlemethod,简称FPM),提出了一种新的点对体积的离散(point-to-volume discretization,简称PTVD)界面接触算法。该算法实际是将界面接触力等价转换为接触点附近两组粒子间的外部相互作用力。具体是根据接触界面特点将接触面两侧物体离散后的粒子划分为主体粒子和从属粒子,对于每个接触点附近的从属粒子,根据其影响域所包含的主体粒子情况确定该粒子与接触面的相对关系计算法向接触力,根据其影响域内两类粒子的相对切向速度和界面摩擦系数计算切向接触力。PTVD接触算法可避免界面粒子识别及精确模拟等相关的复杂接触力计算,充分体现了光滑粒子法的非局部特点。在利用经典界面接触和摩擦算例进行验证的基础上,将PTVD算法应用于颗粒土拟静力坍塌和弹体侵彻软土等涉及接触界面的大变形土力学问题SPH数值分析,结果表明PTVD算法在摩擦接触问题的SPH数值分析中具有有效性和广泛适用性。

Solving frictional contact problems by two aggregate-function-based algorithms

Three dimensional frictional contact problems are formulated as linear complementarity problems based on the parametric variational principle. Two aggregate-functionbased algorithms for solving complementarity problems are proposed. One is called the self-adjusting interior point algorithm, the other is called the aggregate function smoothing algorithm. Numerical experiment shows the efficiency of the proposed two algorithms.

有砟道床人工捣固作业模型建立及力学性能分析

为研究人工捣固作业对道床质量状态的作用机理,基于离散元与多体动力学耦合的建模方法,建立人工捣固装置-散体道床仿真模型,有效模拟工人的捣固作业过程,并通过现场试验结果验证模型的正确性,分析人工捣固作业对道床刚度及接触状态的影响。研究结果表明:人工捣固作业会使道床刚度降低,作业后支承刚度为101.85 kN/mm,降低了28.48%,回弹刚度为206.77 kN/mm,降低了9.02%;在捣入及振捣阶段,道砟间接触状态发生改变,同时轨枕下方与道砟颗粒的接触数目增多,有利于枕下空隙的填充;在撤镐阶段,道砟配位数逐渐增大,法向接触力分布趋向均匀,有利于道床的稳定;人工捣固作业有效减小了轨枕周边区域道砟间接触状态的差异。

月球车与月壤交互作用的离散元-多体动力学耦合建模

目前,对于散体颗粒物质与复杂机械系统的耦合作用研究,面临着跨尺度、计算规模庞大以及非光滑表面的接触检测困难等问题。为了探究月球车与月壤交互作用,首先对颗粒-多体耦合系统动力学建模与接触算法进行研究。分别用离散元方法(discrete element method, DEM)和多体动力学(multibody dynamics, MBD)笛卡尔方法建立了散体球形颗粒和含约束多体系统的动力学模型,并基于Hertz-Mindlin模型计算颗粒与刚体的接触力,在此基础上给出顺序耦合策略,建立了离散元和多体耦合的动力学模型。针对月球车齿状车轮的非光滑表面与颗粒之间接触检测规模庞大的问题,提出了非光滑形状物体的分区域局部检测方法,降低了局部检测的规模。通过对比圆柱体冲击颗粒的试验和仿真结果,验证了离散元-多体耦合模型的准确性。在耦合动力学建模和接触算法研究的基础上,对具有齿状车轮的月球车在月壤上行驶过程进行动力学仿真,研究不同驱动参数下的系统动力学特性以及不同轮胎形状对行驶运动的影响,研究结果表明,交错形轮齿的月球车相较直齿形轮齿前进距离多14%,前进效率较高,该研究对月球车的设计具有理论指导意义。

融合GBWO与ENN的人体尺寸预测模型

为了提高人体尺寸预测的效率和准确性,该文提出了GBWO-ENN(Grey Black Wolf Optimization-Elman Neural Network)的方法。针对传统灰狼算法易于陷入局部最优和无法平衡全局与局部搜索的平衡性问题,提出了GBWO算法。该算法融合黑寡妇优化算法中蜘蛛的运动方式对灰狼优化算法中α狼位置更新进行了优化,通过非线性递减的方法降低了收敛系数,并且提出了按位置等级更新种群的策略。随后采用GBWO算法对Elman神经网络的权值和阈值进行优化,并将GBWO-ENN模型应用于三维人体尺寸预测。实验结果表明,GBWO-ENN模型结构简单,能够准确预测人体尺寸,具有较好的预测能力。

基于高速视觉的非接触式振动特性识别方法

针对传统视觉振动测量方法测量高频振动误差较大的问题,提出了采用高速相机搭建非接触测量系统的方法。首先,对高速相机采集图像进行预处理,降低噪声干扰;其次,通过ORB特征点检测方法检测出图像中的特征点,使用Harris评价准则代替原算法中的非极大值抑制方法,从中挑选本文算法提取出的特征点,并通过稀疏光流法对特征点的振动进行追踪,得到准确的特征点位移信息;再次,利用快速傅里叶变换计算出各特征点的振动频率;最后,以音叉和钢条为对象进行实验。实验结果表明,提出的方法在测量结果上与理论计算结果相近,最大误差仅为0.75%,运行速度较传统算法提高约33.22%。

基于智能算法的齿轮副传动优化设计

为对两级渐开线圆柱齿轮减速器的齿轮结构进行优化设计,根据齿轮强度计算标准和机械结构优化设计的相关理论,分析了对齿轮接触强度和弯曲强度较大有影响的参数,以最小中心距为目标函数,以齿轮强度、尺寸等为约束条件,建立了两级渐开线圆柱齿轮传动结构优化的数学模型。基于智能算法(遗传算法)对齿数、模数、螺旋角等参数进行多目标优化,优化后齿轮的最小中心距减少了28.99%,有效的提高了空间利用率。同时该文研究结果可为智能设计、智能制造提供参考。

带铁心横磁-纵磁触头结构的优化设计

触头作为真空灭弧室的核心元件,其灭弧能力会直接影响直流开断过程。该文通过有限元仿真软件建立了三种触头模型,计算了高频电流下触头产生的磁场分布。电流峰值时的触头间隙中心可产生约为21 mT的纵向磁场,横向磁感应强度约为71 mT,纵向磁场分布不均匀。为了进一步提高触头间隙磁场强度以及分布均匀度,在触头模型中增加铁心及改变铁心结构来提升触头产生的磁场强度,基于BP神经网络与智能优化算法联合的方法对触头模型进行优化设计。优化结果显示:当触头的结构参数外触头非径向开槽夹角α为31.8°、外触头内外半径差值Δ为8.3 mm、内触头片半径r为15.2 mm、外触头杯斜槽高度h为16.1 mm、铁心结构开槽宽度d为1.1 mm时,触头间隙中心产生了74.99 mT的横向磁场;电流峰值时刻的触头间隙中心可产生44.02 mT的纵向磁场,不均匀度从优化前的7.44减小到4.67,均匀度得到了较大提升,提高了磁场对真空电弧的调控能力。

结构参数影响的角接触球轴承接触特性及生热分析

为了预测不同工况下主轴轴承的生热量,课题组基于轴承准静态模型和局部法生热模型,提出了一种考虑结构参数影响下的角接触球轴承生热量预测方法。依据Jones滚道控制理论,确定了轴承接触角和接触载荷参数求解方法;采用Newton-Raphson迭代算法,计算了变转速、变外部载荷和变结构参数影响下的角接触球轴承接触参数和生热量。仿真预测结果表明结构参数对轴承接触参数和生热量影响比较显著。利用结构参数的影响规律,为复杂工况下的轴承设计优化和热优化提供了参考。

高速重载弧齿锥齿轮齿面多目标优化设计

以提高弧齿锥齿轮强度性能和减振降噪为出发点,基于TCA(Tooth contact analysis)、LTCA(Load tooth contact analysis)及局部综合法建立高重合度与低啮合转换处传动误差幅值的齿面多目标优化设计模型;利用带精英策略非支配排序遗传算法(NSGA-Ⅱ)优化3个齿面2阶接触参数,根据目标函数重要程度从Pareto最优解集中选择最终优化解。结果表明:给定工况下,优化后的2阶参数使得弧齿锥齿轮副重合度增加了16.69%,啮合转换处传动误差幅值降低了87.33%;同时承载传动误差均值、齿面接触应力均值与大小轮齿根弯曲应力均值分别降低了11.82%、0.25%、12.32%和13.61%,改善了齿轮副的强度性能和啮合性能,实现了减振降噪的效果。

面向脱轨后被动安全防护的转向架结构优化

为了验证和优化列车转向架部件的脱轨后被动安全防护效果,提出基于多边形接触模型的列车脱轨后接触建模方法,并建立列车脱轨后动力学模型,模拟不同结构参数组合下的列车脱轨后运行行为。将所得横移量和结构参数组合作为反向传播神经网络模型的训练样本,拟合两者之间的非线性关系,采用基于锦标赛选择的自适应遗传算法搜索横移量最小解及其对应的参数组合。以拖车制动盘优化问题为例,运用该优化模型进行结构参数优化。研究结果表明:在100 km/h脱轨速度下,制动盘的最优结构参数组合的半径为335 mm、厚度为80 mm、安装位置为320 mm;与原设计相比,车辆脱轨后横移量减少80.2%,大幅度提高了制动盘被动安全防护能力。本文所提出的建模方法和优化模型可推广应用于其他列车结构的脱轨后被动安全防护能力优化和验证,具有较大的工程实用价值。

高铁接触网系统可靠性评估与维修计划决策

研究目的:针对高速铁路接触网系统四种维修方式,本文以接触网系统可靠性最高和维修费用最低为目标,建立基于维修方式组合的预防维修系统多目标优化模型,提出一种改进多目标粒子群优化算法对该模型进行求解。首先采用PWLMC混沌映射生成初始化种群,增强种群多样性,然后采取非线性递减的惯性权重调整策略,提高算法寻优精度和收敛速度。在种群进化过程中,对每一代粒子使用归一化越界处理方法,防止算法陷入早熟。研究结论:(1)提出的改进多目标粒子群优化算法与现有算法相比,Pareto最优解前端的分布范围更广且种群多样性及获得的最优解精度均有提高;(2)在维修次数取13的情况下,改进算法获得的维修方案及该方案下各部件的动态可靠性能均达到较理想效果;(3)改进多目标粒子群优化算法可在满足实际安全运行的要求下得到最优决策方案,有效减低接触网系统维修费用的同时提高其可靠性,为高速铁路接触网系统可靠性评估与维修计划决策提供有效方法。