Linear constraint

[TUDoR]

I have a problem where I like to give a LINK between two nodes + a constant
value of my choice. Is there any possibility to handle such a case in an elegant
way?

example of the desired constraint:
dof 2 of node 1 = dof 2 of node 2 - 0.1

[JStorm]

I want to bring this question on top again:

Is there a way using FEAP commands to add linear multipoint constraints
without Augmented Lagrangian Multipliers but with the elimination method?

a1 * DOF1 + a2 * DOF8 + aX * DOFx + .... = 0

[Prof. R.L. Taylor]

Currently, feap does not include any elimination method for constraints.  It would be useful if any user has implemented one to post the result.

[Prof. R.L. Taylor]

I am curious as to how you want to specify the linear constraint, and how many you need to impose?  Any description would help us consider implementing a multi-point-constraint option.

[JStorm]

Dear Prof. Taylor,

my experiences with FEAP  actually are to limited to propose a well design syntax for the input file. my first idea is something like:

Code: [Select]

MultiPointConstraint, constraintID
  NodeID1 DOFnr a1
  NodeID2 DOFnr a2
  ...
  NodeIDn DOFnr an
to define a homogeneous linear constraint. To my mind the extension to non-homogeneous linear constraints is not needed because it can be obtained by adding a further node to the model and the homogeneous equation, and prescribe a displacement boundary condition to the new node.

The number of possible multi-point-constraints should be arbitrary. (Of course the number is limited by the number of DOFs of the model)

[Nish]

Dear FEAP community,

Is there any possibility to apply linear multi freedom constraints in FEAP?

Regards,
Nish

[JStorm]

FEAP has the LINK feature to tie two degrees of freedom, but not a generalised multi-point constraint implementation.

At my institute, we have implemented multi-point constraints via elimination method into FEAP.
My colleague has extended the implementation to parFEAP and implemented a Lagrange multiplier version for multi-point constraints.

We have sent an early version of the code to FEAP some years ago.
But the user interest in that feature seems quite low.
Hence, it was never considered for integration into official FEAP.

[Nish]

Many thanks JStorm for your help.
Link is fine for me at this moment. just I do not know how to link too many pair nodes, for example I want to link node 502 to node 151,
                                                                                                                                                                             503 to node 152,
                                                                                                                                                                              .
                                                                                                                                                                              .
                                                                                                                                                                              .
                                                                                                                                                                              852 to 501

Do you maybe know how should i do this?

[JStorm]

If the node pairs are in planes, then ELINk could be helpful for you.

You also can make use of the LOOP feature to update the variables with the node IDs and call the LINK command.

Most general is to create a user macro umesh*.f to do the job.

[Prof. S. Govindjee]

LINK also has generation, so if your nodes have regular intervals in terms of node numbers then you can used the generation feature of LINK.  See chapter 11 of the user manual.

[Nish]

Thank you JStorm and prof. Govindjee. It is done.