无轨伸缩式门式起重机接触部位的有限元分析

非线性接触分析在处理接触问题时可以更加接近工程实际,但在实际应用中,接触参数设置复杂、计算效率低以及计算收敛性难以保证等因素制约了它的实用性。节点耦合分析是不存在收敛问题的线性分析,计算成本比接触分析低。为了探讨2种模型在应用中的差异,研究节点耦合线性分析代替非线性接触分析的可行性,以起重量为12 t的无轨伸缩式门式起重机为例,在有限元分析软件ANSYS中分别构建其接触模型和节点耦合模型,考虑接触刚度和摩擦系数对计算结果的影响,在伸缩支腿全伸的工况下比较2种模型下无轨伸缩式门式起重机各接触部位等效应力值的差异。通过对比计算结果发现：2种模型中,最大等效应力均出现在车架施加起升载荷处,计算值相差1.3%,结果差异不大。由于节点耦合分析忽略了摩擦系数,所以2种模型中各接触部位等效应力值存在差异,根据接触部位的相对滑动,在接触模型中选择合适的摩擦系数可减小此差异。研究结果表明：考虑接触区域相对滑动对计算结果的影响,节点耦合分析能较好地模拟接触分析,对于精度要求不高或接触区域基本无相对滑动的模型,可采用节点耦合分析这种简化方式来代替接触分析,以提高计算效率。     

高空真多层绝热低温管道中波纹管简化有限元模拟方法

基于有限元方法对高真空多层绝热(HV-MLI)低温管道进行多场耦合分析时,由于内管道波纹管几何及材料的非线性特性,使整个分析过程极为耗时,限制了有限元法在HV-MLI低温管道优化设计中的应用。为提高有限元分析效率,结合HV-MLI低温管道对所受载荷的响应特征,提出了用Combine14弹簧单元或等截面管等效替代波纹管的方法。通过对Combine14弹簧单元和等截面管相关参数的理论计算及定义,建立了两种HV-MLI低温管道内管的等效有限元计算模型,并对含波纹管、Combine14弹簧单元及等截面管内管道模型分别进行了有限元模拟计算,得到了各模型内管的应力及变形结果。结果表明:建立的两种等效模型合理、有效;与含波纹管模型相比,两种等效模型均在保证分析精度的同时,将分析效率提高了300倍;相比含Combine14弹簧单元模型,含等截面管模型在结构不连续处的应力集中程度较轻,且与含波纹管模型相符,更适于HV-MLI低温管道的多场耦合分析。     

旋翼桨叶结构载荷计算方法比较研究

基于有限转角假设,建立了刚柔耦合旋翼动力学模型。该模型考虑了刚体转动与弹性变形之间的耦合效应,相较于基于小转角假设的传统有限元模型具有明显的优势。气动力以广义力形式与桨叶刚体转动及弹性变形耦合组建方程。在方程求解的单步上,分别采用力积分法、反力法以及曲率法计算桨叶剖面结构振动载荷。以BO105模型桨叶及SA349/2小铃羊直升机为仿真对象,比较研究了这三种载荷计算方法的预测精度与适用范围。对于不考虑气动力的纯结构振动载荷,三种计算方法具有相同的精度。在气弹瞬态计算中,力积分法对桨根载荷的预测精度不足。曲率法与反力法在桨叶有限元节点处得到了相近的结果。反力法预测精度取决于有限元建模精度,且只对节点处载荷有效。由于曲率法只计入弹性桨叶的弯曲曲率,该方法需要更高阶次的形函数以满足自由度二阶导数的连续性。此外,为加速收敛及减少累积误差,本文开发了基于外推法的数值积分算法。     

滚动轴承接触的非线性有限元分析

利用MSC.Patran/Marc软件建立了滚动轴承的二维有限元分析模型,进行了接触非线性有限元分析,得到接触应力、应变随接触状态的变化情况.当不考虑摩擦接触时,压力与变形间呈现一定的非线性关系.当考虑摩擦接触时,下板面最大等效应力增加,应力分布形状发生改变,最大切向应力发生点向接触部位靠近,说明摩擦因素对接触表面切向应力大小与最大切向应力发生点产生影响.     

考虑轮轨接触损失的列车乘员舒适性分析

为探究轮轨接触损失条件下列车乘员舒适性的差异,基于经典半空间10自由度车-桥耦合动力模型,运用集中质量法并引用动态单元法,建立了一个考虑轮轨接触损失的半空间13自由度人车-线耦合动力模型,并开发了一个完整的C++求解程序。计算所得某高架桥铁路运行路段通车时的轨道振动加速度,与实测值进行对比,其峰值波峰波谷间隔极为接近,验证了模型的有效性。基于该模型分析了不同轨道不平顺谱下,车体和等效人体的振动响应,并比较研究了各轨道不平顺谱下车体和等效人体的振动差异。结果表明:不同的轨道不平顺质量将引起车体、等效人体的不同振动响应;且各不同的轨道不平顺质量下,车体和等效人体的振动响应均有所差异。现有以车体振动响应为输入计算评价列车舒适性的方法,并不符合实际工况。该研究中13自由度人车模型与桥梁耦合的同时还考虑了轮轨接触损失的工况,并以等效人体动力响应为输入来计算乘员舒适性,计算结果满足现有的高标准舒适性要求。     

基于结点6自由度的输电线舞动有限元分析

传统的输电线3自由度舞动分析模型无法考虑扭转与平动的耦合作用及扭转运动的非线性。基于空间曲梁理论的应变—位移关系,建立了具有3个平动自由度和3个转角自由度结点的覆冰输电线舞动分析有限元模型。考虑覆冰导线所受空气动力的非线性和导线大幅运动的几何非线性,利用虚功原理建立基于更新Lagrange格式的覆冰导线非线性运动方程。采用 Newmark时间积分和 Newton-Raphson非线性迭代法求解有限元方程。算例分析表明, 利用结点6自由度覆冰导线单元计算输电线的静动力及舞动分析是准确的。对输电线的舞动分析表明,输电线的抗弯截面模量对输电线的平动和扭转有较大的影响。     

列车动力荷载作用下大跨度斜拉桥局部振动响应研究EI北大核心CSCD

为研究列车动力荷载引起的大跨度斜拉桥主梁和桥面板局部动力响应,基于车-桥耦合动力学理论建立了列车-轨道-斜拉桥空间耦合动力学模型。采用固定界面模态综合法和等效正交异性板法建立大跨度斜拉桥精细化三维有限元模型,车辆简化为具有二系悬挂的31自由度弹簧-质量模型,轮轨关系采用可分离的三维轮轨滚动接触模型。以主跨为1 092 m的沪通长江大桥为例,研究了轨道不平顺激励条件下高速列车行驶引起的桥面板和主桁架梁的动力响应特征及分布规律。研究结果表明:固定界面模态综合法既可以有效减少模型自由度数目,又可以反映桥梁局部动力响应;等效正交异性板法虽能较好地反映桥面板的局部振动,但由于没有考虑等效前后主梁整体刚度的一致性,故所计算的主梁振动位移偏差较大;由于桥面板局部竖向刚度较小,桥梁行车线正下方的桥面板竖向加速度远大于主梁桁架节点竖向加速度,建议我国相关铁路桥梁规范在评估大跨度板桁斜拉桥振动加速度时,考虑桥面板局部振动的影响;列车动力荷载作用下主梁桁架杆件应力冲击系数较小,动力效应不显著。     

列车动力荷载作用下大跨度斜拉桥局部振动响应研究

为研究列车动力荷载引起的大跨度斜拉桥主梁和桥面板局部动力响应,基于车-桥耦合动力学理论建立了列车-轨道-斜拉桥空间耦合动力学模型。采用固定界面模态综合法和等效正交异性板法建立大跨度斜拉桥精细化三维有限元模型,车辆简化为具有二系悬挂的31自由度弹簧-质量模型,轮轨关系采用可分离的三维轮轨滚动接触模型。以主跨为1 092 m的沪通长江大桥为例,研究了轨道不平顺激励条件下高速列车行驶引起的桥面板和主桁架梁的动力响应特征及分布规律。研究结果表明:固定界面模态综合法既可以有效减少模型自由度数目,又可以反映桥梁局部动力响应;等效正交异性板法虽能较好地反映桥面板的局部振动,但由于没有考虑等效前后主梁整体刚度的一致性,故所计算的主梁振动位移偏差较大;由于桥面板局部竖向刚度较小,桥梁行车线正下方的桥面板竖向加速度远大于主梁桁架节点竖向加速度,建议我国相关铁路桥梁规范在评估大跨度板桁斜拉桥振动加速度时,考虑桥面板局部振动的影响;列车动力荷载作用下主梁桁架杆件应力冲击系数较小,动力效应不显著。     

空间薄壁截面梁非线性有限单元模型

基于Timoshenko梁理论和Vlasov薄壁杆件理论,通过设置单元内部节点并对弯曲转角和翘曲角采取独立插值的方法,建立了可考虑横向剪切变形和扭转剪切变形及其耦合作用、弯扭耦合、以及二次剪应力影响的空间薄壁梁非线性有限元模型。以更新的拉格朗日格式描述的几何非线性应变推得几何刚度矩阵。同时考虑了材料非线性,假定材料为理想塑性体,服从Von Mises屈服准则和Prandtle-Reuss增量关系,采用有限分割法,由数值积分得到空间薄壁梁的弹塑性刚度矩阵。算例表明该文所建梁单元模型具有良好的精度,适用于空间薄壁结构的有限元分析。     

高精密厂房中高精密平台控制仿真模拟

为进一步提高高精密厂房中平台的隔振效果,在平台控制中考虑超磁致伸缩作动器的非线性特性对多自由度平台混合控制系统产生一定的制约作用,因此将四个超磁致伸缩作动器模型植入混合控制系统进行设计。首先建立一个以空气弹簧和超磁致伸缩作动器为基本元件的多自由度微振动混合控制系统,然后利用Jiles-Atherton模型的概念建立超磁致伸缩作动器的非线性及其逆补偿模型,并将所建立的作动器模型与多自由度微振动控制系统结合。最后对基于作动器模型的混合控制系统与被动控制系统下的高精密平台响应进行对比分析,取得较好的控制效果,为其在实际工程应用中提供可靠的理论依据。     

准双曲面齿轮动态啮合性能的有限元分析研究

研究准双曲面齿轮动态啮合有限元分析模型的构建方法,建立了合理的有限元模型。基于接触动力学的基本理论和显式有限元分析方法,对准双曲面齿轮的动态啮合性能进行了研究,得到啮合接触冲击特性、齿面接触区域、齿面接触应力及齿根弯曲应力等在轮齿动态啮合过程中的变化规律。以转速和负载两个典型的工作条件为变量,建立对比分析模型,研究转速和负载对准双曲面齿轮动态啮合性能的影响。转速对准双曲面齿轮动态啮合性能影响显著,而负载对准双面齿轮的动态啮合性能影响则跟转速有关,随着转速的增大,相同的负载变化对动态啮合性能的影响逐渐减弱。     

A new nine‐node solid‐shell finite element using complete 3D constitutive laws

The solid‐shell element presented in this paper has nine nodes: eight are classically located at the apexes and are fitted with three translational DOFs whereas the ninth is sited at the center and is endowed with only one DOF; a displacement along the ‘thickness’ direction. Indeed, to be used for modeling thin structures under bending effects, this kind of finite element has a favored direction where several integration points are distributed. Besides, there is solely one ‘in‐plane’ quadrature point to avoid locking phenomena and prohibitive CPU costs for large nonlinear computations. Because a reduced integration is not enough to completely prevent transverse shear locking, a shear–strain field is assumed. Compared with the other eight‐node ‘solid‐shell' bricks, the presence of a supplementary node has a main aim: getting a linear normal strain component which, along with a full three‐dimensional constitutive strain–stress behavior, allows to achieve similar results in bending cases as those obtained with the usual plane stress state hypothesis. For that, the ninth node DOF plays the role of an extra parameter essential for a quadratic interpolation of the displacement in the thickness direction. The advantage is that this DOF has a physical meaning and, for instance, a strength equivalent to a normal pressure can be prescribed. With a suitable nodal numbering, the band width is not significantly increased and meshes can easily be generated because the extra nodes are always located at element centers. To emphasize the peculiar features of such an element, a set of examples (linear and nonlinear) is carried out. Numerous comparisons with other elements show pretty good results in bending dominating problems while adding the event of a normal stress component in sheet metal forming simulations with double side contact. Copyright © 2012 John Wiley & Sons, Ltd.     

4‐node unsymmetric quadrilateral membrane element with drilling DOFs insensitive to severe mesh‐distortion

The unsymmetric finite element method is a promising technique to produce distortion‐immune finite elements. In this work, a simple but robust 4‐node 12‐DOF unsymmetric quadrilateral membrane element is formulated. The test function of this new element is determined by a concise isoparametric‐based displacement field that is enriched by the Allman‐type drilling degrees of freedom. Meanwhile, a rational stress field, instead of the displacement one in the original unsymmetric formulation, is directly adopted to be the element's trial function. This stress field is obtained based on the analytical solutions of the plane stress/strain problem and the quasi‐conforming technique. Thus, it can a priori satisfy related governing equations. Numerical tests show that the presented new unsymmetric element, named as US‐Q4θ, exhibits excellent capabilities in predicting results of both displacement and stress, in most cases, superior to other existing 4‐node element models. In particular, it can still work very well in severely distorted meshes even when the element shape deteriorates into concave quadrangle or degenerated triangle.     

含裂纹离心压缩机叶轮结构的振动局部化

针对离心压缩机在复杂运行工况下的失谐与裂纹问题,研究裂纹与失谐对叶轮结构振动响应和振动局部化的影响规律。首先,采用三维有限元模型建立具有复杂几何形状的叶轮结构的定量分析模型,并通过在裂纹界面上定义接触的形式模拟裂纹的呼吸效应。其次,通过采用混合界面模态综合法对系统自由度进行缩减,以解决了采用三维有限元模型分析非线性系统动态响应时所存在的计算量大和收敛困难的问题。最终,采用Monte Carlo方法对含裂纹的失谐叶轮结构进行统计分析,研究随机失谐和裂纹故障对叶轮结构振动局部化的影响规律。结果表明裂纹和失谐都会对结构的振动响应产生显著的影响,并会导致振动能量的集中和振动局部化现象。     

High‐performance geometric nonlinear analysis with the unsymmetric 4‐node, 8‐DOF plane element US‐ATFQ4

A recent unsymmetric 4‐node, 8‐DOF plane element US‐ATFQ4, which exhibits excellent precision and distortion‐resistance for linear elastic problems, is extended to geometric nonlinear analysis. Since the original linear element US‐ATFQ4 contains the analytical solutions for plane pure bending, how to modify such formulae into incremental forms for nonlinear applications and design an appropriate updated algorithm become the key of the whole job. First, the analytical trial functions should be updated at each iterative step in the framework of updated Lagrangian formulation that takes the configuration at the beginning of an incremental step as the reference configuration during that step. Second, an appropriate stress update algorithm in which the Cauchy stresses are updated by the Hughes‐Winget method is adopted to estimate current stress fields. Numerical examples show that the new nonlinear element US‐ATFQ4 also possesses amazing performance for geometric nonlinear analysis, no matter whether regular or distorted meshes are used. It again demonstrates the advantages of the unsymmetric finite element method with analytical trial functions.     

A nine node finite element for analysis of geometrically non-linear shells

A nine node finite element is presented for the analysis of thin shell structures undergoing large deflection. The finite element formulation is based on the concept of degenerate solid shell element and the Hellinger-Reissner principle with independent strain. Three versions of assumed independent strain are selected to suppress spurious kinematic modes. One version leads to a finite element model which is kinematically stable at element level while the other two give globally stable models. Numerical tests indicate that the finite element model which is stable at element level may reveal the locking effect in certain cases. However, the other two models are free of locking.     

地铁车辆-轨道耦合振动响应分析及轨道结构参数优化

针对在建杭州地铁3号线下穿某文教区工程,根据车辆-轨道耦合动力学理论,分别建立车辆-普通整体道床轨道耦合动力学模型和车辆-钢弹簧浮置板轨道耦合动力学模型。基于赫兹非线性接触关系,实现轮轨间的力平衡和位移协调。利用有限元软件ABAQUS,对两种轨道结构模型的动力响应进行计算,研究轮轨耦合动力相互作用机理和轨道振动源强特性,分析浮置板长度、轨道不平顺、扣件刚度、钢弹簧刚度和行车速度对钢弹簧浮置板轨道动力特性的影响,并对轨道结构参数进行优化。研究成果可为该地铁轨道的减振设计提供科学依据。     

某直升机主减传动系统振动能量传递特性研究

基于超单元方法和节点有限元法建立考虑轴系柔性和机匣柔性的齿轮-转子-机匣耦合系统动力学模型,推导了各类齿轮副的啮合关系,以直升机主减速器为研究对象,通过振动响应试验验证了模型的有效性。从振动能量的角度研究耦合和不耦合柔性机匣两种情况下,齿轮副作为振动激励源时系统模型中产生的多级齿轮激励现象和作为传递结构时对振动能量的传递特性。研究结果表明:耦合机匣后,各级齿轮振动能量贡献占比的极值点数量减少,与目标点相邻的齿轮激励源在该节点处振动能量贡献占比整体上升,不相邻的齿轮激励源在该节点处能量贡献占比整体下降;齿轮啮合刚度和啮合阻尼比的增加会提高齿轮副对振动能量的传递能力,啮合误差的增加会降低其对振动能量的传递能力,而耦合柔性机匣会放大齿轮啮合特性对其振动能量传递能力的影响。     

Projection‐based model reduction for contact problems

To be feasible for computationally intensive applications such as parametric studies, optimization, and control design, large‐scale finite element analysis requires model order reduction. This is particularly true in nonlinear settings that tend to dramatically increase computational complexity. Although significant progress has been achieved in the development of computational approaches for the reduction of nonlinear computational mechanics models, addressing the issue of contact remains a major hurdle. To this effect, this paper introduces a projection‐based model reduction approach for both static and dynamic contact problems. It features the application of a non‐negative matrix factorization scheme to the construction of a positive reduced‐order basis for the contact forces, and a greedy sampling algorithm coupled with an error indicator for achieving robustness with respect to model parameter variations. The proposed approach is successfully demonstrated for the reduction of several two‐dimensional, simple, but representative contact and self contact computational models. Copyright © 2015 John Wiley & Sons, Ltd.