How to define "servo-links"

Yuri S.

Hi, 

Does anybody know how to enforce a "servo-link" between two nodes?
I mean a link such that allows me to enforce the displacement of one node as the displacement of another node times a scaling factor.

Thanks
Yuri

Adriano Koga_20259

For OptiStruct you can use the concept of an MPC (equation).

Analysis>>equations.

 

MPCs allows you to create couplings between your nodes/dofs by prescribing an equation. Literally you're adding an equation to your system matrix.

 

The equation involves a independent node/dof, and a dependent node/dof, pretty like the RBE2 concept (which is essentially a bunch of equations).

 

your equation is always written as a summation, equaling 0.0:

wi*indep_node_dofA + wd*dep_node_dofB = 0.0

so, if you want, for example, the X displacement of the dependent node to be 3times the Y displacement of the independent node, then your equation will basically be:

(-1.0)*indep_node_dof2(Y) + (3.0)*dep_node_dof1(X) = 0

isolating:

>>  3.0*dep_node_dof1(X) = 1.0*indep_node_dof2(Y) 

 

Another example:

node1X has to follow node2X.

The equation factors are just.

-1.0node1X + 1.0node2X = 0

 

For using your equation, after creating these inside a load collector, you need to turn it on, as MPCs into your loadstep in order to activate them in your subcase.

Hope this helps you.