Enforced diplacement problems

[y32k]

I'm trying to load a model using enforced displacement and can't get it to work. I've tried using solids and shells with no results. It works fine with beam elements. I've tried both displacement and rotations, loaded on the geometry and nodes, but neither generate any results.
I must be missing something, because I can create the loads without any problems. Any help would be appreciated.

 

[truckcab]

What kind of analysis are you taking about? Dynamic/static?

The SPCD card works well in both cases.
i.e.
SPCD,NODEID,DOF(1-6),DISPLACEMENT
SPCD,100,4,0.5 (rotation 0.5 rad of node 100)


If, however, you run a modal transient dynamic analysis then the SPCD way of applying forced displacement prevents you from using residual vectors.

Live Long and Prosper !

 

[y32k]

I'm doing a static analysis. I'm using SPCD as you indicated. I did manage to find an example on the Noran website similar to what I'm trying to do. Their model works fine, and I can't find any differences between the two, except for the material properties. I only have the modulus and nu specefied, but I don't see why that would make any difference.
Is there a switch in the analysis options that I'm missing?

 

[truckcab]

Hmm... rotation of a solidelement node will not work since solid elements do not have any rotational degrees of freedom, not either do a common shell as CQUAD4 have any stiffness in the "drilling freedom" i.e. in plane rotation of the node. But you have tested translations as well? Otherwise, this might be the reason to your problems?

No, if your analysis is linear and static, then E and nu will do. There must be another thing causing your problem.

 

[truckcab]

By the way? Do you receive an error message or do you simply get a "null" answer?

 

[Onda]

You should constrain the node You want to move with an SPC1 card and call the SPCD with a LOAD card

As an exemple:

$
$ FILENAME - CONST2.DAT
$
ID LINEAR,CONST2
SOL 101
TIME 200
CEND
TITLE = ENFORCED DISPLACEMENTS USING SPC1 ONLY
DISP(PLOT) = ALL
SPC = 1
SUBCASE 1
LOAD = 11
SUBCASE 2
LOAD = 12
BEGIN BULK
PARAM POST 0
$
SPC1 1 123456 1 51 2551 2601
$
SPCD 11 1 3 0.0
SPCD 11 51 3 0.0
SPCD 11 2551 3 5.0
SPCD 11 2601 3 5.0
$
SPCD 12 1 3 0.0
SPCD 12 51 3 5.0
SPCD 12 2551 3 5.0
SPCD 12 2601 3 0.0
$
INCLUDE ’const.bulk’
$
ENDDATA

As a final comment, if the SPCD entry is the only loading in the model, a warning message
is issued alerting you to the fact that no loading is specified for your model. If you intended
for the SPCD entry to be the only loading condition, you may safely ignore this warning
message.

Onda

 

[y32k]

I got the enforced displacements to work. I don't know what happened, all I did was create the same model with a new file instead of overwriting an old one, but that works now. I didn't know rotations wouldn't work; that's what I started with. I was just getting null results, no errors or warnings.

Thanks for the help

 

[johnhors]

Nodes of solid elements only have translational degrees of freedom, so enforcing rotations at these nodes does nothing.

 

[smegger61]

You may find that keeping the old run files such as *.xdb was preventing the overwriting re-run of the analysis working correctly as it can corrupt the new run. It's a good idea to delete (or rename/compress a file you may want to keep) previous run files before running the analysis deck again.