Ghost reactions

[Tom76]

Hello there,

I have a small problem that emerges in Postprocessing.

After analysing a model of a scaffold I'm using Freebody to check reaction loads on the wheels.
However a "Ghost reaction" emerges on the scaffold itself, on a place where no constraints are defined.
See also the attached picture.

Does anyone have a clue where this reaction could come from?
I already tried a rebuild of the model, but this doesn't make any difference.
The reaction keeps appearing.

Thanks for your help.

Tom

 

[rb1957]

do you have AutoSPC on ?

output to print file, .f06, and look at how NASTRAN has interpreted your model.

 

[Tom76]

Thank you for your reply.

Normally I always have AutoSPC on, set to Eigenvalue. And no problems so far.
However, I remodelled the elements adjacent to the "Ghost reaction".
After analysing the structure again the ghost reaction was gone.
So the problem is solved, although I still don't know where it came from.

Anyway, thanks once more.

Tom

 

[rb1957]

maybe you needed an exorcism ?

 

[BlasMolero]

Dear Tom,
This is very easy, check the NX NASTRAN input file generated by FEMAP, you will see there the SPC1 constraints prescribed to the "ghost" node.
Also, make sure to uldate to the latest version of FEMAP, we run now on version 10.3.1.B, I remember that version 10.3.1.A fixed a problem with free body display, here you are the details:


SUBJECT: Femap 10.3.1-A patch is available
----------------------------------------------------------------------------

Dear FEMAP Customer:

Please be advised that a few problems have been discovered in the new Free
Body Post-Processing Tool incorporated in FEMAP v10.3.0 and v10.3.1.


• The first issue affects the Free Body data related to tetra and wedge
elements (with and without mid-side nodes) as well as tri elements with
mid-side nodes. Results on other elements are not affected and their answers
should match older versions and f06 results.

• The second issue relates to the display of freebody resultant vectors
shown in user-defined coordinate systems. If all 3 components were not
selected for the resultant calculation, then the resultant vector would be
displayed in the global rectangular coordinate system instead of the
user-defined coordinate system.

This patch also corrects a problem in Parasolid that would cause FEMAP to
exit unexpectedly when removing certain faces from a solid.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[Tom76]

Dear Blas,

Thank you for your reply.
Now I know where to look, in case I encouter this problem again.

Best regards,
Tom