爱华网coupling分为两种：运动耦合和分布耦合；是对接触问题的一种简化方式，一般来讲，分布耦合处的刚度小于运动耦合处的刚度；
【1】运动耦合：即在此区域的各节点与参考点之间建立一种运动上的约束关系。
【2】分布耦合：
在此区域的各节点与参考点之间建立一种约束关系，但是对此区域上各节点的运动进行了加权处理，使在此区域上受到的合力和合力距与施加在参考点上的力和力矩相等效。换言之，分布耦合允许面上的各部分之间发生相对变形，比运动耦合中的面更柔软。
Products: Abaqus/Standard Abaqus/Explicit Abaqus/CAE
References
Overview
The surface-based coupling constraint:
Surface-based coupling definitions
The surface-based coupling constraint in Abaqus providescoupling between a reference node and a group of nodes referred toas the “coupling nodes.” This option provides the samefunctionality as the kinematic coupling constraint and thedistributing coupling elements (DCOUP2D, DCOUP3D) inAbaqus/Standard with a surface-based user interface. The couplingnodes are selected automatically by specifying a surface and anoptional influence region. The procedure used to define thecoupling nodes is discussed below.
For a distributing coupling constraint, the distributing weightfactors are calculated automatically if the surface is anelement-based surface. In such a case the weight factors are basedon the tributary area at each coupling node, except for a surfacealong a shell edge, where the weight factors are based on thetributary edge length. Furthermore, the distributing weight factorscan be modified using one of several weighting methods, which allowthe forces transferred to the coupling nodes to vary inversely withthe radial distance from the reference node.
Typical applications
The coupling constraint is useful when a group of coupling nodesis constrained to the rigid body motion of a single node. Thecoupling constraint can be employed effectively in the followingapplications:
Defining the coupling constraint
Defining a coupling constraint requires the specification of thereference node (also called the constraint control point), thecoupling nodes, and the constraint type. The coupling constraintassociates the reference node with the coupling nodes. A name mustbe assigned to the constraint and may be used in postprocessingwith Abaqus/CAE. A node number or node set name may be specifiedfor the reference node. If a node set is specified, the node setmust contain exactly one node. The reference node for a kinematiccoupling constraint has both translational and rotational degreesof freedom. The surface on which the coupling nodes are located canbe node-based; element-based; or, in Abaqus/Explicit, a combinationof both surface types. You can specify an optional radius ofinfluence that limits the coupling nodes to a specific region onthe surface. Details on how coupling nodes are defined byspecifying an influence region are discussed below.
The constraint type can be either kinematic or distributing, asdiscussed below.
| Input File Usage: | Use the followingoptions: |
*COUPLING, CONSTRAINT NAME=name, REF NODE=n, SURFACE=surface*KINEMATIC or *DISTRIBUTING |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Coupling type:Kinematic orDistributing |
Specifying a region of influence
By default, coupling nodes belonging to the entire surface areselected for the coupling definition. You can limit the couplingnodes to lie within a spherical region centered about the referencenode by defining a radius of influence.
The procedure by which coupling nodes are selected for theconstraint definition depends on the surface type:
| Input File Usage: | *COUPLING, CONSTRAINT NAME=name, REF NODE=n, SURFACE=surface, INFLUENCE RADIUS=r |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Influence radius:Specify |
Kinematic coupling constraints
Kinematic coupling constrains the motion of the coupling nodesto the rigid body motion of the reference node. The constraint canbe applied to user-specified degrees of freedom at the couplingnodes with respect to the global or a local coordinate system.
Kinematic constraints are imposed by eliminating degrees offreedom at the coupling nodes. In Abaqus/Standard once anycombination of displacement degrees of freedom at a coupling nodeis constrained, additional displacement constraints—such as MPCs,boundary conditions, or other kinematic coupling definitions—cannotbe applied to any coupling node involved in a kinematic couplingconstraint. The same limitation applies for rotational degrees offreedom. This restriction does not apply in Abaqus/Explicit. See“Kinematic constraints:overview,” Section 31.1.1, formore information.
| Input File Usage: | Use both of thefollowing options to define a kinematic couplingconstraint: |
*COUPLING*KINEMATICfirst dof, last dof For example, the following coupling constraint is used toconstrain degrees of freedom 1, 2,【】 and 6 on surface surfA to reference node 1000: *COUPLING, CONSTRAINT NAME=C1, REF NODE=1000, SURFACE=surfA*KINEMATIC1, 26, |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Coupling type:Kinematic:toggle on the degrees of freedom |
Translational degrees of freedom
Translational degrees of freedom are constrained by eliminatingthe specified degrees of freedom at the coupling nodes. When alltranslational degrees of freedom are specified, the coupling nodesfollow the rigid body motion of the reference node.
Rotational degrees of freedom
Rotational degrees of freedom are constrained by eliminating thespecified degrees of freedom at the coupling nodes.
All combinations of selected rotational degrees of freedomresult in rotational behavior identical to existing MPC types:
In Abaqus/Standard internal nodes are created by the kinematiccoupling to enforce the constraints that are equivalent to MPCtypes REVOLUTE and UNIVERSAL. These nodes have the same degrees offreedom as the additional nodes used in these MPC types and areincluded in the residual check for nonlinear analysis.
Specifying a local coordinate system
The kinematic coupling constraint can be specified with respectto a local coordinate system instead of the global coordinatesystem (see “Orientations,” Section 2.2.5). Figure 31.3.2–1 illustrates the use of a local coordinatesystem to constrain all but the radial translation degrees offreedom of the coupling nodes to the reference node. In thisexample a local cylindrical coordinate system is defined that hasits axis coincident with the structure's axis. The coupling nodeconstraints are then specified in this local coordinate system.
| Input File Usage: | *COUPLING, ORIENTATION=local |
For example, the following input is used to specify the kinematiccoupling constraint shown in Figure 31.3.2–1: *ORIENTATION, SYSTEM=CYLINDRICAL, NAME=COUPLEAXIS0.0, -1.0, 0.0, 0.0, 1.0, 0.0*COUPLING, REF NODE=500, SURFACE=Endcap, ORIENTATION=COUPLEAXIS*KINEMATIC2, 3 |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Edit: select localcoordinate system |
Constraint direction and finite rotation
In geometrically nonlinear analysis steps the coordinate systemin which the constrained degrees of freedom are specified willrotate with the reference node regardless of whether theconstrained degrees of freedom are specified in the globalcoordinate system or in a local coordinate system.
Distributing coupling constraints
Distributing coupling constrains the motion of the couplingnodes to the translation and rotation of the reference node. Thisconstraint is enforced in an average sense in a way that enablescontrol of the transmission of loads through weight factors at thecoupling nodes. Forces and moments at the reference node aredistributed either as a coupling node-force distribution only(default) or as a coupling node-force and moment distribution. Theconstraint distributes loads such that the resultants of the forces(and moments) at the coupling nodes are equivalent to the forcesand moments at the reference node. For cases of more than a fewcoupling nodes, the distribution of forces/moments is notdetermined by equilibrium alone, and distributing weight factorsare used to define the force distribution.
The moment constraint between the rotation degrees of freedom atthe reference node and the average rotation of the cloud nodes canbe released in one direction in a two-dimensional analysis and one,two, or three directions in a three-dimensional analysis. In athree-dimensional analysis you can specify the moment constraintdirections in the global coordinate system or in a local coordinatesystem. All available translational degrees of freedom at thereference node are always coupled to the average translation of thecoupling nodes.
In a three-dimensional Abaqus/Standard analysis if all threemoment constraints are released by specifying only degrees offreedom 1 through 3, only translation degrees of freedom will beactivated on the reference node. If only one or two rotationdegrees of freedom have been released, all three rotation degreesof freedom are activated at the reference node. In this case youmust ensure that proper constraints have been placed on theunconstrained rotation degrees of freedom to avoid numericalsingularities. Most often this is accomplished by using boundaryconditions or by attaching the reference node to an element such asa beam or shell that will provide rotational stiffness to theunconstrained rotation degrees of freedom.
In Abaqus/Explicit releasing one or more of the momentconstraints may lead to significant computational performancedegradation. This is also the case when other constraints intersectthe cloud of coupling nodes. In these cases, the degradation inperformance is particularly noticeable when a large number of suchdistributed couplings are present in the model or when the size ofthe constrained “cloud” is large. For that matter, when themodeling conditions mentioned above are encountered, the size ofthe coupling nodes cloud is limited to 1000. To alleviate thereleased moment constraint issue, the following modeling techniquecan be used (also available in Abaqus/Standard): constrain allmoments in the distributed coupling and use an appropriateconnector element at the reference node (such as REVOLUTE, HINGE, CARDAN or BUSHING) to model released moments at thecoupling's reference node. This technique has also the advantage ofbeing able to specify finite compliance such as elasticity,plasticity or damage in the “released” rotational component.
| Input File Usage: | *DISTRIBUTINGfirst dof, last dof |
If no degrees of freedom are specified, all available degrees offreedom are coupled. If you specify one or more rotation degrees offreedom but not all available translation degrees of freedom,Abaqus issues a warning message and adds all available translationdegrees of freedom to the constraint. For example, the following coupling constraint is used toconstrain degrees of freedom 1–5 on the reference node 1000 to theaverage translation and rotation of surface surfA: *COUPLING, CONSTRAINT NAME=C1, REF NODE=1000, SURFACE=surfA*DISTRIBUTING1, 5 In this example the moment constraint between the reference nodeand the coupling nodes will be released in the 6-direction but willbe enforced in the 4- and 5-directions. This provides a“revolute-like” rotation connection between the reference node andthe coupling nodes (see “General multi-pointconstraints,” Section31.2.2). |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Coupling type:Distributing:toggle on the rotational degrees of freedom (Abaqus/CAEautomatically constrains the translational degrees of freedom) |
Node-based surface
User-defined weight factors are used for node-based surfaces.The cross-sectional areas specified in the surface definition areused as the weight factors (see “Node-based surfacedefinition,” Section2.3.3).
Element-based surface
For element-based surfaces the weight factors are calculated byAbaqus. The default weight distribution is based on the tributarysurface area at each coupling node, except for a surface along ashell edge where the weight distribution is based on the tributaryedge length. The procedure used to calculate the default weightfactors is designed to ensure that if a radius of influence isprescribed, the default weight distribution varies smoothly withthe influence radius.
Calculating the default distributing weightfactors
The procedure to calculate the distributing weight factorsdepends on whether or not an influence radius is specified.
Calculating the facet participation factor
The participation factor defines the proportion of the facet'sarea that contributes to the distributing weight factors when aninfluence radius is specified. The participation factor variesbetween zero and one.
To define the participation factor, the distance of the facetnode closest to the reference node, , and the distance of the facet nodefarthest from the reference node, , are calculated.
If all coupling nodes fall outside the influence radius (i.e., for all facets), Abaqus selects all nodesbelonging to the closest facets (as outlined under “Specifying aregion of influence”) and uses a participation factor equal to one.Weighting methods
You can modify the default weight distribution defined above.Various weighting methods are provided that monotonically decreasewith radial distance from the reference node. For each case thedefault weight distribution that is based on the tributary surfacearea (or tributary edge length along a shell edge) is scaled by theweight factor . If the weighting method is notspecified, a uniform weighting method is used in which all weightfactors are equal to 1.0.
Linearly decreasing weight distribution
A linearly decreasing weighting scheme
where is the weight factor at coupling nodei, is the coupling node radial distance fromthe reference node, and is the distance to the furthest couplingnode.| Input File Usage: | *DISTRIBUTING, WEIGHTING METHOD=LINEAR |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Coupling type:Distributing:Weightingmethod: Linear |
Quadratic polynomial weight distribution
A quadratic polynomial weight distribution defined by
| Input File Usage: | *DISTRIBUTING, WEIGHTING METHOD=QUADRATIC |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Coupling type:Distributing:Weightingmethod: Quadratic |
Monotonically decreasing weight distribution
A monotonically decreasing weight distribution according to thecubic polynomial
| Input File Usage: | *DISTRIBUTING, WEIGHTING METHOD=CUBIC |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Coupling type:Distributing:Weightingmethod: Cubic |
Specifying a local coordinate system
The distributing coupling constraint can be specified withrespect to a local coordinate system instead of the globalcoordinate system (see “Orientations,” Section 2.2.5). Figure 31.3.2–2 illustrates the use of a local coordinatesystem to release the moment constraints between the reference nodeand the coupling nodes in the local 4- and 6-directions, providinga “universal-like” rotation connection. In this example a localrectangular coordinate system is defined that has its localy-axis coincident with theglobal z-axis. The momentconstraint is specified in this local coordinate system.
| Input File Usage: | *COUPLING, ORIENTATION=local |
For example, the following input is used to specify thedistributing coupling constraint shown in Figure 31.3.2–2: *ORIENTATION, SYSTEM=RECTANGULAR, NAME=COUPLEAXIS0.0, 1.0, 0.0, 0.0, 0.0, 1.0*COUPLING, REF NODE=500, SURFACE=Endcap, ORIENTATION=COUPLEAXIS*DISTRIBUTING1, 35, 5 |
| Abaqus/CAE Usage: | Interaction module: Create Constraint: Coupling: Edit: select localcoordinate system |
Defining the surface coupling method
There are two methods available to couple the motion of thereference node to the average motion of the coupling nodes: thecontinuum coupling method and the structural coupling method. Thecontinuum coupling method is used by default.
Continuum coupling method
The default continuum coupling method couples the translationand rotation of the reference node to the average translation ofthe coupling nodes. The constraint distributes the forces andmoments at the reference node as a coupling nodes forcedistribution only. No moments are distributed at the couplingnodes. The force distribution is equivalent to the classic boltpattern force distribution when the weight factors are interpretedas bolt cross-section areas. The constraint enforces a rigid beamconnection between the attachment point and a point located at theweighted center of position of the coupling nodes. For furtherdetails, see “Distributing coupling elements,” Section 3.9.8 of the Abaqus TheoryManual.
| Input File Usage: | *DISTRIBUTING , COUPLING=CONTINUUM |
| Abaqus/CAE Usage: | Coupling the motion of the reference node to theaverage motion of the coupling nodes is not supported inAbaqus/CAE. |
Structural coupling method
The structural coupling method couples the translation androtation of the reference node to the translation and the rotationmotion of the coupling nodes. The method is particularly suited forbending-like applications of shells when the coupling constraintspans small patches of nodes and the reference node is chosen to beon or very close to the constrained surface. The constraintdistributes forces and moments at the reference node as a couplingnode-force and moment distribution. For this coupling method to beactive, all rotation degrees of freedom at all coupling nodes mustbe active (as would be the case when the constraint is applied to ashell surface) and the constraints must be specified in all degreesof freedom (default). In addition, for the constraint to bemeaningful, the local (or global) z-axis used in the constraint should besuch that it is parallel to the average normal direction of theconstrained surface.
With respect to translations, the constraint enforces a rigidbeam connection between the reference node and a moving point thatremains at all times in the vicinity of the constrained surface.The location of this moving point is determined by the approximatecurrent curvature of the surface, the current location of theweighted center of position of the coupling nodes (see “Distributing coupling elements,” Section 3.9.8 of the Abaqus TheoryManual), and the z-axisused in the constraint. This choice avoids unrealistic contactinteractions if multiple pairs of distributed coupling constraintsare used to fasten shell surfaces (see “Breakable bonds,” Section 33.1.9, for more details).
With respect to rotations, the constraint is different alongdifferent local directions. Along the z-axis (twist direction), theconstraint is identical to the one enforced via the continuumcoupling method (see “Distributing coupling elements,” Section 3.9.8 of the Abaqus TheoryManual). By contrast, the rotational constraint in the planeperpendicular to the z-axisrelates the in-plane reference node rotations to the in-planerotations of the coupling nodes in the immediate vicinity of thereference node. This choice provides a more realistic (compliant)response when the constrained surface is small and deformsprimarily in a bending mode.
| Input File Usage: | *DISTRIBUTING, COUPLING=STRUCTURAL |
| Abaqus/CAE Usage: | Coupling the motion of the reference node to theaverage motion of the coupling nodes is not supported inAbaqus/CAE. |
Moment release and finite rotation
In geometrically nonlinear analysis steps the coordinate systemof the degrees of freedom that define the moment release rotateswith the reference node regardless of whether the global coordinatesystem or a local coordinate system is used.
Colinear coupling node arrangements
The distributing coupling constraint transmits moments at thereference node as a force distribution among the coupling nodes,even if these nodes have rotational degrees of freedom. Thus, whenthe coupling node arrangement is colinear, the constraint is notcapable of transmitting all components of a moment at the referencenode. Specifically, the moment component that is parallel to thecolinear coupling node arrangement will not be transmitted. Whenthis case arises, a warning message is issued that identifies theaxis about which the element will not transmit a moment.
