Utilities to handle ccx issues with shells in steady state dynamics


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.

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)