球轴承柔性多体动力学分析与接触振动研究

结合有限元法和柔性多体动力学方法,提出球轴承柔性多体接触动力学模型和动力学分析方法。综合考虑钢球与内外圈滚道的游隙、柔性多体接触、套圈弹性变形、摩擦、离心力和转速等关键因素,建立球轴承的柔性多体接触动力学模型。研究了球轴承的柔性多体动力学特性和接触振动响应,计算出球轴承钢球公转一周时的接触力变化、套圈中心的相对振动位移、加速度、套圈弹性变形、截面接触应力和径向接触应力等接触振动响应,揭示了球轴承的支承钢球数目奇偶交替时的变柔性接触振动本质。提出的球轴承动力学模型与计算结果为以系统振动为目标的球轴承动态设计和球轴承系统设计提供理论指导和参考数据。     

柔性多体系统碰撞动力学研究

摘 要：针对工程中常见的柔性多体系统碰撞过程,详细的分析了柔性多体系统的接触碰撞条件,基于非线性等效弹簧阻尼模型建立了柔性体的碰撞模型,并基于库仑摩擦模型考虑两体碰撞时的切向摩擦作用。在此基础上把柔性体碰撞模型综合到柔性多体系统动力学方程中,建立了含接触碰撞的柔性多体系统动力学模型,此模型适用于一般含碰撞的多体系统。仿真算例以柔性梁在重力场中的接触碰撞过程为对象进行动力学仿真,研究柔性梁碰撞前、碰撞过程及碰撞后的动力学特性和动态响应,以及碰撞过程碰撞力的变化规律,并与刚性梁在重力场中的接触碰撞过程进行详细的比较和分析,结果表明基于非线性等效弹簧阻尼模型建立的柔性多体系统碰撞动力学模型可以有效的分析接触碰撞过程的动力学性能,验证了模型的有效性和正确性。     

考虑三维圆柱铰间隙碰撞的空间机构柔性多体动力学分析方法

三维圆柱铰的动态性能对空间机构的运动精度和动力学特性有着重要的影响。基于多体动力学方法和刚体有限元方法,提出考虑三维圆柱铰的间隙碰撞和动态接触作用的空间机构柔性多体接触动力学方法。采用圆柱-圆柱的线接触力学模型和切片法,计算圆柱-圆柱的接触变形量和接触力,建立三维圆柱铰的轴销与轴套之间的间隙碰撞作用和三维动态接触关系。以等效刚体单元和Timoshenko梁单元描述柔性杆件的刚性有限元模型,建立柔性连杆和三维圆柱铰的具有多刚体系统的统一形式的动力学方程。计算分析了含三维圆柱铰的空间机构的运动精度和动力学特性,获得空间机构的位移响应,三维圆柱铰的相对运动轨迹和动态作用力等动力学响应。采用三维圆柱-圆柱动态线接触方法,能有效地预测空间机构系统的三维圆柱铰持续接触、间隙碰撞状态和摩擦作用下的动力学特性。计算结果表明三维圆柱铰的间隙碰撞作用对空间机构的运动精度和动态特性的影响较为显著。动力学模型和计算结果对复杂工况下高精度多间隙的空间机构的动态设计和动力学研究具有重要的理论意义。     

水平轴风力机柔性叶片多体动力学建模与动力特性分析

为用较少自由度实现水平轴风力机柔性叶片气弹耦合分析,用超级单元（Superelement）方法将柔性叶片离散为由带有力元弹簧及阻尼器的旋转铰连接的有限个数体,基于多体动力学理论,应用R-W（Roberson-Wittenburg)方法导出叶片多体系统动力学微分-代数方程组;研究方程组数值积分方法及通过脉冲响应谱实现系统动力特性分析方法;分析某1.5 MW风力机叶片在脉冲载荷作用下的动力响应与固有频率,并通过与ANSYS、ADAMS结果对比验证方法及编制程序的有效性与正确性。结果表明,超级单元法能用较少自由度准确描述柔性叶片弹性变形与动力载荷与叶片位移间耦合,为风力机气动弹性耦合及稳定性分析提供实用分析方法。     

基于虚拟样机技术的曲轴多体动力学仿真

基于虚拟样机技术和柔性多体动力学理论,综合运用三维建模,有限元分析以及多体动力学仿真等技术,建立包括曲轴柔性体以及随曲轴一起转动的零件刚性体在内的整个曲轴系统的虚拟样机模型,通过进行曲轴系统在发动机真实工况下的柔性多体动力学仿真计算,得到了各构件之间相互作用力,继而得到曲轴在一个工作循环周期内的实时动力学响应,为曲轴的优化设计奠定了基础.     

往复泵曲柄连杆机构振动特性分析

运用刚性和柔性多体系统动力学理论,对舱底泵曲柄连杆机构进行运动学和动力学计算,分析出其主要激励力频率和大小,并运用多体系统动力学软件Adams,对其进行运动学、动力学仿真和振动分析。结果表明,用柔性多体动力学理论将机构柔性化,能够更加准确揭示其振动特性,对往复泵设计和低噪声修理具有重要参考意义。     

接触界面对拉杆组合柔性转子轴承系统的非线性动力特性影响

对于拉杆柔性组合转子轴承系统,其接触界面类型复杂、数量众多,是影响其动力特性的众多因素之一。以拉杆柔性组合转子轴承系统各轮盘间的接触界面为考察对象,根据接触界面压力结合微观模型有限元分析,得到其宏观尺寸下的界面接触刚度。采用无质量无长度的均质面弹簧对接触界面进行等效,推导了接触界面作为附加弹簧单元对系统产生附加刚度矩阵的一般形式,并完成了计及接触界面效应的系统动力学建模。结合应用计及轴向力的铁木辛格梁轴单元的整体转轴建立的有限元模型,得到系统的动力学方程。而后采用打靶法和Floquet稳定性判别理论对系统进行分析求解,得到了计入接触界面影响后系统的稳定性边界和分叉形式,数值结果表明接触界面对不平衡组合转子的动力特性影响不可忽略。     

刚柔耦合多体系统动力学模型降阶

提出了基于模态综合法的刚柔耦合多体系统动力学模型降阶方法。该方法用自然坐标法和绝对节点坐标法分别描述刚柔耦合多体系统中的刚体构件和柔性体构件,同时用Craig-Bampton方法对柔性体模型进行减缩。对于刚体构件与柔性体构件之间只存在线性约束的情况,建立了消除线性约束的刚柔耦合多体系统动力学方程。最后,为了验证的该方法的有效性,对刚柔耦合双摆进行了研究。仿真结果表明:适当选择模态就可以在满足计算精度的同时减少计算时间,提高计算效率。     

大规模接触转台系统动力学建模与仿真

在分析了大型柔性转台研制难点的基础上,提出了采用多柔体动力学方法进行大型柔性转台系统的建模与仿真.在解决柔性轴承大规模接触问题建模的前提下,建立了某柔性转台系统的多柔体虚拟样机,基于该虚拟样机获得了转台撑腿、外环、钢珠的位移和应力随时间、空间的变化特性.最后基于多体动力学的仿真分析结果完成了整个转台系统的疲劳寿命仿真分析.本文所建立的大型柔性转台的虚拟样机为其正式产品的工程设计验证提供了有力的技术手段.     

计及应力刚化效应的空间大运动曲梁动力学建模与分析

从连续介质力学非线性位移-应变关系出发,导出计入应力刚化效应的空间柔性梁变形能表达式。利用浮动框架有限元方法和哈密顿变分原理推导了满足小变形假设的空间曲梁的一般运动动力学方程,并利用模态缩减法对动力学方程进行了维数降阶。所推导的动力学方程可用于高速旋转一般运动空间柔性曲梁动力学问题的求解。通过数值仿真讨论了应力刚化效应对大范围运动小变形空间柔性曲梁动力学特性的影响,并与ADAMS软件和ABAQUS软件的仿真结果进行了对比,指出了ADAMS软件在高速旋转柔性多体系统数值计算方面的一些缺陷。所提出的计及应力刚化效应的空间曲梁动力学建模方法为高速旋转一般运动柔性多体系统动力学建模和分析提供了参考。     

The Discontinuity‐Enriched Finite Element Method

We introduce a new methodology for modeling problems with both weak and strong discontinuities independently of the finite element discretization. At variance with the eXtended/Generalized Finite Element Method (X/GFEM), the new method, named the Discontinuity‐Enriched Finite Element Method (DE‐FEM), adds enriched degrees of freedom only to nodes created at the intersection between a discontinuity and edges of elements in the mesh. Although general, the method is demonstrated in the context of fracture mechanics, and its versatility is illustrated with a set of traction‐free and cohesive crack examples. We show that DE‐FEM recovers the same rate of convergence as the standard FEM with matching meshes, and we also compare the new approach to X/GFEM.     

An interface‐enriched generalized FEM for problems with discontinuous gradient fields

A new generalized FEM is introduced for solving problems with discontinuous gradient fields. The method relies on enrichment functions associated with generalized degrees of freedom at the nodes generated from the intersection of the phase interface with element edges. The proposed approach has several advantages over conventional generalized FEM formulations, such as a lower computational cost, easier implementation, and straightforward handling of Dirichlet boundary conditions. A detailed convergence study of the proposed method and a comparison with the standard FEM are presented for heat transfer problems. The method achieves the optimal rate of convergence using meshes that do not conform to the interfaces present in the domain while achieving a level of accuracy comparable to that of the standard FEM with conforming meshes. Various application problems are presented, including the conjugate heat transfer problem encountered in microvascular materials. Copyright © 2011 John Wiley & Sons, Ltd.     

Finite cover method with mortar elements for elastoplasticity problems

Finite cover method (FCM) is extended to elastoplasticity problems. The FCM, which was originally developed under the name of manifold method, has recently been recognized as one of the generalized versions of finite element methods (FEM). Since the mesh for the FCM can be regular and squared regardless of the geometry of structures to be analyzed, structural analysts are released from a burdensome task of generating meshes conforming to physical boundaries. Numerical experiments are carried out to assess the performance of the FCM with such discretization in elastoplasticity problems. Particularly to achieve this accurately, the so-called mortar elements are introduced to impose displacement boundary conditions on the essential boundaries, and displacement compatibility conditions on material interfaces of two-phase materials or on joint surfaces between mutually incompatible meshes. The validity of the mortar approximation is also demonstrated in the elastic-plastic FCM.     

用基于流形元的子域奇异边界元法模拟重力坝的地震破坏

本文提出了用流形无法和子域奇异边界元法相结合模拟结构地震响应及地震破坏的方法。流形元法的独特的网格及接触的处理方式,使该方法不仅可以象有限元法那样精确地分析结构的变形和应力,还可以象ＤＤＡ、ＤＥＭ等不连续分析方法那样模拟不连续面的接触和块体的运动．本文将Ｎｅｗｍａｒｋ法引入流形无法,使得该方法可以直接用来分析动力学问题。与作者提出的子域奇异边界元法相结合,可以模拟裂缝沿任意方向扩展及结构的地震破坏问题。对Ｋｏｙｎａ重力坝进行了地震破坏模拟分析,很好地再现了该坝的破坏过程,模拟破坏形式及裂缝出现的位置与实际调查结果、实验结果及其他学者用模糊裂缝模型得到的破坏结果吻合良好。     

基于EEP法的三维有限元超收敛计算初探

二维有限元法（FEM）的超收敛计算,借助有限元线法（FEMOL）作为桥梁,分两步采用单元能量投影（EEP）法导出超收敛公式,初步形成“逐维离散、逐维恢复”的方案。然而这一思路直接应用于三维问题却遇到了困扰:一维问题的EEP解（位移和导数）均可达到相同的超收敛阶,而二维问题却难以做到。研究发现,为了得到三维问题的EEP超收敛位移,只需提供二维问题最低阶的超收敛位移即可。该文按此思路推导了非规则网格下三维六面体单元的EEP超收敛位移公式,给出了一个实施方案,并通过数值算例验证了此方案的有效性。     

Solving electromagnetic problems using a novel symmetric FEM-BEM approach

This paper presents a novel symmetric finite element method-boundary element method (FEM-BEM) formulation for solving unbounded electromagnetic problems. The proposed method offers two very attractive features: 1) it is variational, leading to a symmetric system of equations and 2) the meshes for the computations of FEM and BEM can be nonconformal, leading to decoupled computations of FEM and BEM. The accuracy and efficiency of the method are studied for both electromagnetic radiation and scattering problems.     

A locking‐free selective smoothed finite element method using tetrahedral and triangular elements with adaptive mesh rezoning for large deformation problems

A novel finite element (FE) formulation with adaptive mesh rezoning for large deformation problems is proposed. The proposed method takes the advantage of the selective smoothed FE method (S‐FEM), which has been recently developed as a locking‐free FE formulation with strain smoothing technique. We adopt the selective face‐based smoothed/node‐based smoothed FEM (FS/NS‐FEM‐T4) and edge‐based smoothed/node‐based smoothed FEM (ES/NS‐FEM‐T3) basically but modify them partly so that our method can handle any kind of material constitutive models other than elastic models. We also present an adaptive mesh rezoning method specialized for our S‐FEM formulation with material constitutive models in total form. Because of the modification of the selective S‐FEMs and specialization of adaptive mesh rezoning, our method is locking‐free for severely large deformation problems even with the use of tetrahedral and triangular meshes. The formulation details for static implicit analysis and several examples of analysis of the proposed method are presented in this paper to demonstrate its efficiency. Copyright © 2014 John Wiley & Sons, Ltd.     

Impact Simulation on Ductile Metal Pipe with Polymer Coating by a Coupled Finite Element and Meshfree Method

It is common knowledge that conventional finite element method (FEM) has intrinsic limitations in analyzing large deformation problems like high-velocity impact, explosion, etc. because of mesh distortion and tangling; while these problems can be easily avoided by the meshfree method (MM), the latter involves greater computation time. Therefore, in this article, in order to simultaneously utilize the respective advantages of the two methods, a coupled simulation method between both FEM and MM was employed to analyze the high-velocity impact on ductile metal pipe with polymer coating. The impacted area with large deformation was discretized by SPH (smoothed particle hydrodynamics) particles, a classic meshfree model, and the remaining section was modeled by FEM meshes. By this method, the interfacial shear stresses between the coating and the substrate and the residual stresses beneath the contact points were studied, which would have referenced values in analyzing failure modes of components with similar composite structure. Then, the results were compared with sole FEM and MM too.     

A multiscale DEM-FEM approach to investigate the tire–pavement friction

Abstract

Fundamental understandings of the pavement-tire friction are vital to improve the design of asphalt pavements. Most of the current research on pavement-tire friction is based on Finite Element Method (FEM), which is relatively complex and difficult to simulate the discontinuity during friction. To overcome the limitations, in this paper, the pavement–tire friction process is investigated using a coupled Multi-scale Discrete Element Method (DEM) – FEM approach. The benefit of such a multiscale method is that DEM has the advantage of simulating the discontinuity behaviour during friction, and FEM is good at simulating the continuum material with low computation consumption. The multi-scale approach provides an innovative and promising approach to simulate the tire-pavement friction behaviour.     

An adaptive domain decomposition coupled finite element–boundary element method for solving problems in elasto‐plasticity

The purpose of this paper is to present an adaptive finite element–boundary element method (FEM–BEM) coupling method that is valid for both two‐ and three‐dimensional elasto‐plastic analyses. The method takes care of the evolution of the elastic and plastic regions. It eliminates the cumbersome of a trial and error process in the identification of the FEM and BEM sub‐domains in the standard FEM–BEM coupling approaches. The method estimates the FEM and BEM sub‐domains and automatically generates/adapts the FEM and BEM meshes/sub‐domains, according to the state of computation. The results for two‐ and three‐dimensional applications in elasto‐plasticity show the practicality and the efficiency of the adaptive FEM–BEM coupling method. Copyright © 2009 John Wiley & Sons, Ltd.