Keyword type: model definition
With this keyword distributing constraints can be established between the nodes belonging to an element surface and a reference node. A distributing constraint specifies that a force or a moment in the reference node is distributed among the nodes belonging to the element surface. The weights are calculated from the area within the surface the reference node corresponds with.
The *DISTRIBUTING card must be immediately preceded by a *COUPLING keyword card, specifying the reference node and the element surface. If no ORIENTATION was specified on the *COUPLING card, the degrees of freedom apply to the global rectangular system, if an ORIENTATION was used, they apply to the local system. For a *DISTRIBUTING constraint the local system cannot be cylindrical.
The degrees of freedom to which the distributing constraint should apply, have to be specified underneath the *DISTRIBUTING card. They should belong to the range 1 to 6. Degrees of freedom 1 to 3 correspond to translations along the local axes, if any, else the global axes are taken. Degrees of freedom 4 to 6 correspond to rotations about the local axes (4 about the local x-axis and so on), if any, else the global axes are taken. No matter what the user specifies, forces are always distributed (degree of freedom 1 to 3). Consequently, the only freedom the user has is to decide whether any additional moments should be distributed.
In the degrees of freedom in the reference node a force/moment can be applied by a *CLOAD card. This load system is replaced by an equivalent force distribution in the nodes belonging to the coupling surface. No matter what force and/or moment is applied to the reference node, all translational degrees of freedom of the nodes in the surface are updated. This means that for the first *CLOAD definition in the reference node in a step the parameter OP=NEW is de facto active.
No kinematic relations are created between the reference node and the coupling surface, so applying displacement constraints in the reference node has no effect. In fact, the displacements at the reference node remain zero throughout the calculation. In order to check the force and/or moment in the reference node the user should use *SECTION PRINT to obtain the global force and moment on the selected surface. To check the global displacements of the surface a *DISTRIBUTING COUPLING may be defined for the nodes in the surface. For the global rotations a mean rotation MPC (cf. Section 8.7.1) can be used.
A *DISTRIBUTING coupling is usually selected in order to distribute a force or moment area-weighted among the nodes of a surface. For this to work properly the surface should be plane.
If any of these conditions is not satisfied, the results will be inaccurate.
Example: *ORIENTATION,NAME=OR1,SYSTEM=RECTANGULAR 0.,1.,0.,0.,0.,1. *COUPLING,REF NODE=262,SURFACE=SURF,CONSTRAINT NAME=C1,ORIENTATION=OR1 *DISTRIBUTING 4,4 *NSET,NSET=N1 262 ... *STEP *STATIC *CLOAD 262,4,1.
specifies a moment of size 1. about the local x-axis, which happens to coincide with the global y-axis.
Example files: coupling7, cyl.