RBE3, Master, DOF, Slaves, Wtfact
Distributes the force/moment applied at the master node to a set
of slave nodes, taking into account the geometry of the slave nodes as well
as weighting factors.
MasterNode at which the force/moment to be distributed will be applied. This node must be associated with an element for the master node to be included in the DOF solution.
DOFRefers to the master node degrees of freedom to be used in constraint equations. Valid labels are: UX, UY, UZ, ROTX, ROTY, ROTZ, UXYZ, RXYZ, ALL
SlavesThe name of an array parameter that contains a list of slave nodes. Must specify the starting index number. ALL can be used for currently selected set of nodes. The slave nodes may not be colinear, that is, not be all located on the same straight line (see Notes below).
WtfactThe name of an array parameter that contains a list of weighting factors corresponding to each slave node above. Must have the starting index number. If not specified, the weighting factor for each slave node defaults to 1.
The force is distributed to the slave nodes proportional to the weighting factors. The moment is distributed as forces to the slaves; these forces are proportional to the distance from the center of gravity of the slave nodes times the weighting factors. Only the translational degrees of freedom of the slave nodes are used for constructing the constraint equations. Constraint equations are converted to distributed forces/moments on the slave nodes during solution.
RBE3 creates constraint equations such that the motion of the master is the average of the slaves. For the rotations, a least-squares approach is used to define the "average rotation" at the master from the translations of the slaves. If the slave nodes are colinear, then one of the master rotations that is parallel to the colinear direction can not be determined in terms of the translations of the slave nodes. Therefore, the associated moment component on the master node in that direction can not be transmitted. When this case occurs, a warning message is issued and the constraint equations created by RBE3 are ignored.
Applying this command to a large number of slave nodes may result in constraint equations with a large number of coefficients. This may significantly increase the peak memory required during the process of element assembly. If real memory or virtual memory is not available, consider reducing the number of slave nodes.
As an alternative to the RBE3 command, you can apply a similar type of constraint using contact elements and the internal multipoint constraint (MPC) algorithm. See Surface-based Constraints for more information.
This command is also valid in SOLUTION.