Utilities to handle ccx issues with shells in steady state dynamics

[FEAnalyst]

Hi,

when preparing a simple example of steady state dynamics analysis involving shell elements, I’ve encountered two issues that require specific workarounds in CalculiX:

*ERROR in complexfreq reading the eigenvectors in the eigenvalue file… *INFO in steadystate: if there are problems reading the .eig file this may be due to:
1) the nonexistence of the .eig file
2) other boundary conditions than in the input deck
which created the .eig file

The solution was to remove the *BOUNDARY, OP=NEW keyword and the definition of that boundary condition from the second step so it remains unmodified from the first step. Currently, it’s not possible in PrePoMax but it would be good to have an option to remove the OP=NEW keywords in subsequent steps.

*WARNING: 1-D or 2-D elements may cause problems in steady state calculations
ensure that point loads defined in a *STEADY STATE DYNAMICS step
and applied to nodes belonging to 1-D or 2-D elements have been
applied to the same nodes in the preceding FREQUENCY step with
magnitude zero; look at example shellf.inp for a guideline.

To obtain correct results I had to copy the load definition from the steady state dynamics step to the frequency one, change the magnitudes to 0 and remove the LOAD CASE parameter. This is quite unusual but since it’s a CalculiX limitation, maybe PrePoMax could allow users to use this workaround. Not necessarily by supporting direct definitions of zero-valued loads within the frequency step but possibly by introducing an option for steady state dynamics step that upom activation would do this internally.

[Matej]

I think that number 1 is the same as for the modal dynamics step. Number 2 is new for me.

I will test the behaviours of both points to see what happens.

(I would say it is a little messy to deal with dynamic steps in CalculiX at the moment)

[ANYS]

@FEAnalyst

Not necessarily by supporting direct definitions of zero-valued loads within the frequency step but possibly by introducing an option for steady state dynamics step that upom activation would do this internally

¿Is this managed Internally now?

[FEAnalyst]

No, there’s no such feature yet.

[ANYS]

Thank you very much.

[ANYS]

Hi again and sorry for asking so much,

I’m behind a Dynamic Modal analisys set up which is not working right now.

¿Would there be a way I could load the stored eig file in Prepomax which I know is correct and save some computational time while testing the dynamic part?

I’m tring to add an *include card on top of the keyword editor and jump directly to the dynamic step but it doesn’t seem to work.

Regards

[FEAnalyst]

According to ccx documentation, it should be possible to use the existing .eig file:

These eigenmodes are recovered from a file ”problem.eig”, where ”problem” stands for the name of the structure. These eigenmodes must have been determined in a previous step (STORAGE=YES on the *FREQUENCY card or on the *HEAT TRANSFER,FREQUENCY card), either in the same input deck, or in an input deck run previously.

I haven’t tested it yet, but I guess it will work if you define only the modal dynamic step in the new analysis and use a proper name of the analysis job so that it finds the .eig file (in the same work directory).