冲击-接触问题有限元仿真的并行计算

冲击．接触问题广泛存在于汽车碰撞等的模拟计算中。简单介绍了求解该类问题的显式有限元方法，对显式有限元方法的并行性进行了讨论。根据显式有限元和冲击一接触问题的计算特点，设计并实现了接触均衡的分区算法。算例计算结果表明：该并行算法具有较好的加速比和并行效率。     

带滚珠调节的面-面接触形式负荷传感器球头副

为降低传统负荷传感器球头的接触应力水平,提高传感器测量的准确度和长期可靠性,设计了一种带滚珠调节的面-面接触形式的负荷传感器球头副结构,同时通过对比实验进行了验证,实验结果显示采用该结构的球头副,一只20MN柱式力传感器可在倾斜0.2°的状态下,测量得到重复性小于0.005%、方位误差小于0.04%。研究表明,该带滚珠调节的面-面接触形式负荷传感器球头副相对未带滚珠调节的面-面接触形式传感器球头副,球头相对球碗转动时摩擦阻力更小,不仅能实现水平自调节,而且还能灵活调整由负荷传感器上、下承压面不平行带来的角度偏差,使传感器在不同测量方位测得的载荷输出值更一致,方位误差更小。此外,由于采用了面-面接触形式,该结构球头副接触应力较小,具有较大的承载能力,保证在大载荷作用下具有足够的强度。     

三叶形截面碳纤维的吸波性能研究

模拟了截面形状为三叶形的单根碳纤维在真空中的电磁散射特性。结果表明,单根碳纤维的雷达散射截面(RCS)会随着入射波频率的增加而增加;在入射波频率一定的情况下,单根碳纤维的RCS会随着纤维的长度、横截面面积、电导率的增加而增加,而叶片之间夹角的变化对RCS几乎无影响。     

一种含赫兹接触的梁结构冲击特性分析方法

密封电磁继电器的接触系统可被等效为含有非线性赫兹接触条件的双梁结构力学模型。针对接触系统在冲击振动下容易被“抖断”和“抖闭”的特点,本文结合有限元方法、赫兹接触条件和Newmark β法进行编程仿真,得到了双梁结构接触系统在受到冲击下的动态特性,同时分析了赫兹接触条件对仿真结果的影响。最后借助电磁振动台对接触系统实物模型进行冲击试验,实验结果验证了方法的可行性与准确性。     

汽车造型形面的分类与光影表达

目的探讨汽车造型的内在规律,研究汽车形面的属性。方法以汽车的形面为研究对象,通过对形面分类的研究,观察汽车造型中愈发丰富的形面处理方式;然后对形面的光影进行观察,分析光影的形成原因以及光影的主要检测方式。结论形面已经成为一种重要的汽车造型手法,不同的汽车形面带来不同的审美意味,而形面的光影是形面走势的重要表达,同时也是汽车审美属性的一部分。对汽车造型形面的分类与光影的研究,对于深入了解设计师领域的知识有着重要意义。     

三维冲击-动力接触问题数值分析的一种高效算法

本文要二维冲击－动力接触问题^[3]和三维弹性接触有限元混合法的基础上,给出了三维冲击－动力接触问题的有限元混合算法,该方法将整个系统的等效刚度议程凝缩到接触边界,建立关于接触面的等效柔度方程,在采用Newmark直接积分法求解动力接触问题时必须作适当修正,本文给出了修正方法,由于用直接积分法进行每一时间步动力接触爱代计算时,只震反复求解接触面有效柔度议程,因此具有很高的计算效率。     

熔纺三叶形聚乙烯醇纤维的制备及增强水泥基材料

采用自主创新的聚乙烯醇(PVA)熔融纺丝新技术,首次制备了三叶形截面PVA异形纤维,为水泥基复合材料提供新型增强纤维。研究了熔融纺丝和热拉伸对纤维截面形状、热性能、结晶性能、取向度和力学性能等的影响。结果表明,熔纺三叶形截面PVA初生纤维内部结构均匀致密,无明显皮芯结构。经热拉伸处理,纤维能较好保持三叶形截面,异形度为58.2%。PVA分子链在拉伸应力下诱导结晶,纤维结晶结构更完善,结晶度和取向度增加,纤维的强度增加,熔点升高。热拉伸8倍后,纤维强度达3.7 cN/dtex。将三叶形纤维用于水泥基复合材料的增强增韧,当其体积掺量为2%时,纤维增强水泥试件的挠度达17.3%,断裂能达10.5 J。     

截面形貌对三叶型SiC纤维电磁性能的影响

通过先驱体转化法,制备出三叶形、三折叶形和T形截面SiC纤维。对3种纤维进行了XRD测试,并使用网络分析仪测试了纤维的电磁性能。3种异形SiC纤维具有相同的XRD谱图,但其介电常数有较大差异,模拟结果表明3种纤维具有不同的吸波性能。     

改性三叶形聚乙烯醇纤维/环氧树脂复合材料的结构与性能

异形截面纤维大的比表面积有利于提高纤维与基体树脂间的界面结合,改善复合材料的强度和韧性.文中采用环氧氯丙烷对熔纺三叶形聚乙烯醇(PVA)纤维进行表面改性,通过模压成型首次制备了改性三叶形PVA纤维/环氧树脂复合材料.对比研究了改性前后三叶形PVA纤维表面结构和性能及对复合材料力学性能的影响.结果表明,改性后三叶形PVA...     

基于面接触的车桥耦合振动研究

现有分析车-桥耦合振动的研究中都假设移动车辆与路面的接触关系为点接触。事实上,轮胎与路面是通过面接触的。通过建立新的三维车轮模型,分析了面接触对车-桥耦合振动的影响,将车轮与路面的接触面模拟为长方形,通过接触面间的位移协调条件和力相互作用建立车-桥耦合振动方程。对车速、车轮刚度与阻尼、接触面尺寸大小、车辆数目等进行参数分析,研究了接触面对车-桥耦合振动的影响。数值计算与试验结果验证表明:所提出的模型能更准确合理的研究车桥耦合振动。     

Hyperelastic analysis based on a polygonal finite element method

In this contribution, we present a novel polygonal finite element method applied to hyperelastic analysis. For generating polygonal meshes in a bounded period of time, we use the adaptive Delaunay tessellation (ADT) proposed by Constantinu et al. [1 A. Constantinu, P. Steinmann, T. Bobach, G. Farin, and G. Umlauf, The adaptive Delaunay tessellation: A neighborhood covering meshing technique., Comput. Mech., vol. 42, no. 5, pp. 655–669, 2008.[Crossref], [Web of Science ®] , [Google Scholar]]. ADT is an unstructured hybrid tessellation of a scattered point set that minimally covers the proximal space around each point. In this work, we have extended the ADT to nonconvex domains using concepts from constrained Delaunay triangulation (CDT). The proposed method is thus based on a constrained adaptive Delaunay tessellation (CADT) for the discretization of domains into polygonal regions. We involve the metric coordinate (Malsch) method for obtaining the interpolation over convex and nonconvex domains. For the numerical integration of the Galerkin weak form, we resort to classical Gaussian quadrature based on triangles. Numerical examples of two-dimensional hyperelasticity are considered to demonstrate the advantages of the polygonal finite element method.     

基于LuGre摩擦模型的轮胎多边形磨损机理分析

多边形磨损是汽车轮胎磨损研究中的一个新课题,具有重要的理论价值和研究意义。考虑轮胎接地磨擦的非线性特性,建立了基于LuGre摩擦模型的轮胎多边形磨损的动力学模型。通过仿真给出了能够引起自激振动的车速和轮胎初始前束角范围。这些结果为减小或消除轮胎的自激振动提供了理论依据。     

轮胎多边形磨损的发生机理及其影响因素分析

考虑轮胎接地磨擦的非线性特性,采用由能量法确定的胎面单元侧向刚度计算公式,建立了基于胎面侧向振动的轮胎多边形磨损动力学模型,探讨轮胎多边形磨损现象的发生机理,并通过数值仿真分析了车速、轮胎前束角和垂向载荷对轮胎磨损的影响。结果表明：轮胎多边形磨损为胎面均匀磨损和扰动磨损叠加引起的周向不均匀磨损,是一种典型的非线性自激振动现象,其发生与胎面的侧向振动有关;以李雅普诺夫稳定性理论为基础,指出轮胎的自激振动是一种由系统Hopf分岔引起的稳定周期振动现象;高速、较大的前束角和超载是导致轮胎产生多边形磨损的可能原因。     

基于扭矩控制的导管内径滚压连接成形特征分析

钛合金导管内径滚压连接技术主要用于飞机液压管路系统中,具有耐高压和高密封性,能够提升飞机液压管路系统的高可靠性能,满足飞机轻量化和长寿命的需求,成为航空管件连接技术的首选方案.本文以理论分析、有限元模拟和试验相结合的方法,从导管滚压连接胀形器各组件的运动状态、接触状况、受力分析以及管材节点位移变化等方面,探讨了基于扭矩控制的导管内径滚压连接成形机理及特征.研究表明,成形过程中芯轴主动转动,滚柱带动保持架周向随动转动;芯轴与滚柱之间有较大的径向挤压力和切向摩擦力,在这两个力的合力作用下,产生轴向进给力,使芯轴自动进给,导管、滚柱和芯轴之间接触面和接触力逐渐增大,成形扭矩随之增加,导管材料逐渐嵌入管套凹槽,完成连接成形,这是扭矩控制的导管内径滚压连接机理所在.理论分析与有限元模拟及试验结论吻合较好,研究结果对工程应用中的质量控制和工艺优化具有一定的指导作用.     

Accurate correction of surface noises of polygonal meshes

In this paper we propose a new algorithm for accurate correction of surface noises of polygonal meshes. It consists of three basic components: (a) feature‐preserving pre‐smoothing; (b) partitioning of feature and non‐feature regions; (c) second‐order predictor for non‐feature regions and median filter for feature regions. The unique contributions of our approach include (a) an idea of partitioning an input surface into feature and non‐feature regions so that different smoothing algorithms, which are best suited for either feature or non‐feature regions can be, respectively, applied; (b) a second‐order predictor that provides higher smoothing accuracy and better convergence on smoothly curved surfaces. In comparison with several existing algorithms, our algorithm is evaluated quantitatively in terms of surface normal and vertex distance error metrics. Numerical experiments indicate the effectiveness of our approach in the aspects of convergence and accuracy. Copyright © 2005 John Wiley & Sons, Ltd.     

Arbitrary polygonal cloaks with multiple invisible regions

Arbitrary polygonal cloaks with multiple invisible regions are achieved by transformation optics. The original total space is divided into several layers. Choosing proper spatial mappings for these layers, a few empty layers in which objects can be hidden without bringing any scattering are available as extended invisible regions. Compared with the original polygonal cloaks the proposed one can provide multiple interior and/or exterior invisible regions simultaneously, and the objects can thus be hidden in the interior cavity and/or in the exterior space, or even be embedded into the gap between the cloaking shells.     

Computational Morphogenesis: Morphologic constructions using polygonal discretizations

To consistently coarsen arbitrary unstructured meshes, a computational morphogenesis process is built in conjunction with a numerical method of choice, such as the virtual element method with adaptive meshing. The morphogenesis procedure is performed by clustering elements based on a posteriori error estimation. Additionally, an edge straightening scheme is introduced to reduce the number of nodes and improve accuracy of solutions. The adaptive morphogenesis can be recursively conducted regardless of element type and mesh generation counting. To handle mesh modification events during the morphogenesis, a topology-based data structure is employed, which provides adjacent information on unstructured meshes. Numerical results demonstrate that the adaptive mesh morphogenesis effectively handles mesh coarsening for arbitrarily shaped elements while capturing problematic regions such as those with sharp gradients or singularity.     

A new scheme for efficient and direct shape optimization of complex structures represented by polygonal meshes

In this paper, a new shape optimization approach is proposed to provide an efficient optimization solution of complex structures represented by polygonal meshes. Our approach consists of three main steps: (1) surface partitioning of polygonal meshes; (2) generation of shape design variables on the basis of partitioned surface patches; and (3) gradient‐based shape optimization of the structures by reducing a weighted compliance among all load cases. The main contributions of this paper include (i) that our approach can be directly applied on polygonal meshes with the reduction of design variables or decision variables by 10 to 1000 times, compared to the conventional design variable scheme of using each mesh node; (ii) our perturbation scheme is mathematically proven with respect to maintaining the smoothness of each surface patch, except on its boundary; and (iii) overall, our approach can be used to automate time‐consuming shape optimization of polygonal meshes to a greater extent. Numerical experiments have been conducted and the results indicate the effectiveness of the approach. Copyright © 2003 John Wiley & Sons, Ltd.     

Reduction in mesh bias for dynamic fracture using adaptive splitting of polygonal finite elements

We present a method to reduce mesh bias in dynamic fracture simulations using the finite element method with adaptive insertion of extrinsic cohesive zone elements along element boundaries. The geometry of the domain discretization is important in this setting because cracks are only allowed to propagate along element facets and can potentially bias the crack paths. To reduce mesh bias, we consider unstructured polygonal finite elements in this work. The meshes are generated with centroidal Voronoi tessellations to ensure element quality. However, the possible crack directions at each node are limited, making this discretization a poor candidate for dynamic fracture simulation. To overcome this problem, and significantly improve crack patterns, we propose adaptive element splitting, whereby the number of potential crack directions is increased at each crack tip. Thus, the crack is allowed to propagate through the polygonal element. Geometric studies illustrate the benefits of polygonal element discretizations employed with element splitting over other structured and unstructured discretizations for crack propagation applications. Numerical examples are performed and demonstrate good agreement with previous experimental and numerical results in the literature. Copyright © 2014 John Wiley & Sons, Ltd.