reference to: user manual 18.6

18.6 理解自适应网格（adaptive meshing） 自适应网格可以通过移动独立的材料网格(allowing the mesh to move independently of the material),让你在整个分析过程中即使发生大变形，也能保持高质量的网格。通常自适应网格只移动节点，网格的拓扑并不改变。 注意：通常自适应网格多用在Dynamic（动态分析），Explicit and Dynamic（显示动态分析）, Temp-disp, Explicit 中。 定义模型中某个区域采用自适应网格的设置：other-->Adaptive Mesh Domain 自适应网格的选项控制设置:Other--〉Adaptive Mesh Controls 通常，在每一个step中只能有一个自适应网格区域。 21.2.1 ABAQUS/Standard defines contact between two bodies in terms of two surfaces that may interact; these surfaces are called a “contact pair.”ABAQUS/Standard defines “self-contact,” which is available only in two-dimensional analysis, in terms of a single surface. [if gte vml 1]> <![endif][if !vml][endif]Figure 21.2.1–1 Contact and interaction discretization. 从the first surface (the “slave” surface)的节点向 the second surface (the “master” surface)做垂线，寻找最近的垂线的垂足，The interaction is then discretized between the point on the master surface and the slave node. Strict master-slave contact 在这种关系下，主面的节点可以穿入从面（副面），但副面不可以穿入主面。见下图： [if gte vml 1]> <![endif][if !vml][endif] In the strict master-slave contact formulation used in ABAQUS/Standard, only the master surface is used as a surface, where its geometry and orientation are taken into consideration. The only data that ABAQUS/Standard needs from the slave surface are the location of its nodes and the surface area associated with each node; the direction of the slave surface's normal is not relevant in strict master-slave contact. Thus, a slave surface can be defined as a group of nodes—a node-based surface. Generally, the master surface should be chosen as the surface of the stiffer body or as the surface with the coarser mesh if the two surfaces are on structures with comparable stiffnesses. The stiffness of the structure and not just the material should be considered when choosing the master and slave surface. For example, a thin sheet of metal may be less stiff than a larger block of rubber even though the steel has a larger modulus than the rubber material. If the stiffness and mesh density are the same on both surfaces, the preferred choice is not always obvious. General restrictions on surfaces used in contact pairs When creating a surface that may be used as a master surface in a contact or interaction analysis, the contact algorithm in ABAQUS/Standard imposes the following restrictions on the master surface: [if !supportLists]· [endif]The master surface must be element-based or analytical. [if !supportLists]· [endif]The master surface must have the proper orientation. [if !supportLists]· [endif]The master surface must be continuous. [if !supportLists]· [endif]In finite-sliding mechanical contact simulations the master surface should be smoothed See “Defining element-based surfaces,” Section 2.3.2, “Defining node-based surfaces,” Section 2.3.3, and “Defining analytical rigid surfaces,” Section 2.3.4, for general restrictions on defining surfaces 注意，主平面地法线方向必须是向外的，这样才能防止副平面产生集中。如下图： [if gte vml 1]> <![endif][if !vml][endif][if gte vml 1]> <![endif][if !vml][endif] 主平面必须是连续的，它不能够有两个不连续的区域构成——无论是二维还是三维，在两个区域的连接单元的边界处必须连续。 二维情况：surface must be either a simple, nonintersecting curve with two terminal ends or a closed loop。 三维情况：可以是边或者有效单元的单元面（某几个或某一个单元面），但不能是两个单元的公共点。they must be joined across a common element edge。An element edge cannot be shared by more than two surface facets 如下图，显示了有效和无效的主面： [if gte vml 1]> <![endif][if !vml][endif] 21.2.2 在ABAQUS/Standard 中有三个方式来实现接触对的两个面的相对运动。 1 finite sliding：通用方式，允许面以任意方式移动（任意分离、滑动、旋转）（见“Finite-sliding interaction between deformable bodies,” Section 5.1.2 of the ABAQUS Theory Manual, “Finite-sliding interaction between a deformable and a rigid body,” Section 5.1.3 of the ABAQUS Theory Manual)） 2 small sliding：假设尽管两个物体可以产生大的移动，但是会假设一个面相对于另一个面只有很小的相对滑动。（“Small-sliding interaction between bodies,” Section 5.1.1 of the ABAQUS Theory Manual)） 3 infinitesimal sliding and rotation：(无限小 滑移和旋转)假设两个接触面之间的相对运动和绝对运动都很小 1--：Smoothing master surfaces in finite-sliding simulations 使用该选项时，主平面必须是平滑过渡的，其面上的所有节点必须有唯一的法方向，如果平面不连续（例如出现尖角）副节点的移动就会出现集中现象,造成在不连续点粘结。在该选项中，ABAQUS/Standard 会自动平滑基于单元的主平面，For finite-sliding simulations with planar or axisymmetric deformable master surfaces，ABAQUS/Standard会用抛物线来平滑一介不连续单元面，用立方抛物线来平滑二次不连续单元面 如图： [if gte vml 1]> <![endif][if !vml][endif] 可以用SMOOTH parameter on *CONTACT PAIR option to control the degree of smoothing of the master surface in surface-based contact simulations. 可以用SMOOTH parameter on the *SLIDE LINE option for analyses using slide lines and contact elements 在上述情况中都要设定一个参数f, where [if gte vml 1]> <![endif][if !vml][endif], [if gte vml 1]> <![endif][if !vml][endif]and [if gte vml 1]> <![endif][if !vml][endif] is the lengths of the element facets that join at the surface node, and [if gte vml 1]> <![endif][if !vml][endif]。 ABAQUS/Standard会自动在距离不连续节点a1和a2处用2次和3次曲线将两点连接起来。this smoothed segment will be used in the contact calculations。The default value of [if gte vml 1]> <![endif][if !vml][endif]is 0.2. Smoothing affects only segments where the normal to the deformable master surface is discontinuous at the node joining two elements: it does not affect the two segments adjacent to the midside nodes on second-order element faces [if gte vml 1]> <![endif][if !vml][endif] The normal vector of a point within the region bounded by the dashed lines is computed to be normal to the facet. Outside this region it is smoothed with respect to the adjacent facets, using a generalization of the two-dimensional approach shown in Figure and Figure. The default value of [if gte vml 1]> <![endif][if !vml][endif]is 0.2. Usage: For surface-based contact simulations *CONTACT PAIR, INTERACTION=name, SMOOTH=f [if gte vml 1]> <![endif][if !vml][endif]or when using slide lines and contact elements *SLIDE LINE, ELSET=name, SMOOTH=f [if gte vml 1]> <![endif][if !vml][endif] 如果主平面有大变形 如图所示： [if gte vml 1]> <![endif][if !vml][endif]但是福平面也跟着做相应变形，从而主-副面之间并不产生大的相对移动，此时就用small-sliding contact 21．2．3 可以用ADJUST parameter on the *CONTACT PAIR option 让ABAQUS/Standard调整接触对副平面的位置，该参数可以等于浮点数a(主平面 调整区域的宽度，见上面)或者节点设置标签（a node set label），系统会自动调整。 Usage: *CONTACT PAIR, ADJUST= a or node_set_label ADJUST parameter 没有默认值，如果忽略该参数，系统就不会调整副平面。（分别是选项中的第3、4两项） 也可以用，node set label 来调整，adjusts only the slave nodes in the specified node set, any overclosed slave nodes not in the specified node set remain overclosed at the start of the simulation。但是如果有些需要调整的点没有在node set label里，就会造成集中问题。 Initial configuration of the contact surfaces showing the “adjustment zone.” The slave surface is in bold. [if gte vml 1]> <![endif][if !vml][endif] Figure 21.2.3–2 Configuration of the contact surfaces after the adjustment. Nodes within the adjustment zone and overclosed nodes have been moved. [if gte vml 1]> <![endif][if !vml][endif] Figure 21.2.3–3 Adjusted configuration of contact surfaces when using ADJUST=0. [if gte vml 1]> <![endif][if !vml][endif] 图表 [if supportFields]> SEQ 图表 \* ARABIC <![endif]1[if supportFields]><![endif] Defining a precise initial clearance or overclosure This option is used to define initial clearance values and/or contact directions precisely at contact slave nodes. In an ABAQUS/Standard analysis it can also be used to define overclosure values. The *CLEARANCE option can be used with small-sliding contact only (*CONTACT PAIR, SMALL SLIDING). In ABAQUS/Explicit it can be used only in the first step of an analysis. 19.12.1 Creating interactions 根据前面的step的不同，interactions可以从以下选项中选择： [if !supportLists]· [endif]Contact. [if !supportLists]· [endif]Elastic foundations. [if !supportLists]· [endif]Heat flux on a surface due to convection.（只用于 heat transfer, coupled temperature-displacement, or coupled thermal-electrical step.） [if !supportLists]· [endif]Heat flux on a surface due to radiation to the environment. [if !supportLists]· [endif]Interactions between a point and a user-defined actuator/sensor element(只适用于initial step) All contact pair results are given at the nodes of the slave surface：因为只有副面才变形！ Example 1： Mechanical surface interaction with friction and finite sliding. Figure 21.2.1–9 shows the mesh used in this example. For purposes of this example, the surface ASURF is the slave surface of the contact pair. The property definition for the contact pair (GRATING) uses the finite-sliding formulation with a friction model where [if gte vml 1]> <![endif][if !vml][endif]=0.4 and the default “hard” contact model for the behavior normal to the surfaces. Figure 21.2.1–9 Mechanical surface interaction with friction and finite sliding. [if gte vml 1]> <![endif][if !vml][endif]*HEADING …*SURFACE, NAME=ASURFESETA,*SURFACE, NAME=BSURFESETB,*CONTACT PAIR, INTERACTION=GRATINGASURF, BSURF*SURFACE INTERACTION, NAME=GRATING*FRICTION0.4*NSET, NSET=SNODES101, 102, 103*STEP, NLGEOM…*END STEP