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, the translations are always distributed (degree of freedom 1 to 3). Consequently, the only freedom the user has is to decide whether any additional rotational degrees of freedom should be distributed.
The degrees of freedom in the reference node can be constrained by a *BOUNDARY card, or a corresponding force/moment can be applied by a *CLOAD card. The displacements in the reference node can be obtained by selecting U on the *NODE PRINT card. The rotation about the reference node cannot be printed. In order to obtain 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.
A *DISTRIBUTING coupling is usually selected in order to distribute a force or moment area-weighted among the nodes of a surface. In case of a bending moment or torque the rotation takes place about the center of gravity of the surface. Nodes close to the center of gravity usually deteriorate the convergence.
In CalculiX, the *DISTRIBUTING contraint is linear, i.e. the coefficients of the constraint are not updated during the calculation.
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.