Keyword type: model definition
With this keyword kinematic constraints can be established between each node belonging to an element surface and a reference node. A kinematic constraint specifies that the displacement in a certain direction i at a node corresponds to the rigid body motion of this node about a reference node. Therefore, the location of the reference node is important.
This card must be immediately preceded by a *COUPLING keyword card. If no ORIENTATION was specified on the *COUPLING card, the degrees of freedom entered immediately below the *KINEMATIC card (these are the degrees of freedom i which take part in the rigid body motion) apply to the global rectangular system, if an ORIENTATION was used, they apply to the local system. If the local system is cylindrical, the degrees of freedom 1, 2 and 3 correspond to the displacement in radial direction, the circumferential angle and the displacement in axial direction, respectively (as defined by the *ORIENTATION card; the position of the reference node is immaterial to that respect).
The degrees of freedom in the reference node (1 up to 3 for translations, 4 up to 6 for rotations; they apply to the global system unless a *TRANSFORM card was defined for the reference node) can be constrained by a *BOUNDARY card. Alternatively, a force (degrees of freedom 1 up to 3) or moment (degrees of freedom 4 up to 6) can be applied by a *CLOAD card. In the latter case the resulting displacements (degrees of freedom 1 up to 3) can be printed in the .dat file by selecting U on the *NODE PRINT card for the reference node. However, the corresponding selection of RF on the *NODE PRINT card does not work for the reference node. Instead, the user should use *SECTION PRINT to obtain the global force and moment on the selected surface.
Example: *NODE 262,.5,.5,8. *ORIENTATION,NAME=OR1,SYSTEM=CYLINDRICAL .5,.5,0.,.5,.5,1. *COUPLING,REF NODE=262,SURFACE=S1,ORIENTATION=OR1,CONSTRAINT NAME=CN1 *KINEMATIC 2 *STEP *STATIC *BOUNDARY 262,6,6,.01
specifies a moment of size 0.01 about the z-axis through node 262. The rotation (angle) about this axis of each node belonging to the facial surface SURF will be identical and such that the resulting moment in the structure agrees with the applied moment. Since only local degree of freedom 2 takes part in the rigid body motion, the radial and axial displacement in the nodes belonging to surface S1 is left completely free.
Example files: coupling2, coupling3.