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.

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.

Yuri S.

Thank you very much for your help.

Have a nice day