Software Use > FEM Coupling (HyperFEA)

ANSYS Eigenvalue Buckling + Modal Analysis - User defined analysis?

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mraedel:
Hi,

I would like to incorporate a global linear buckling and modal analysis in my sizing using ANSYS. HyperFEA allows the definition of a buckling constraint in the Global FEA Constraints. Unfortunately, it seems not to be implemented yet for use with ANSYS.

I wonder, is it possible to start a linear buckling analysis from HyperSizer using an APDL-script and read the result in HyperSizer using the "User defined analysis"?

Ryan:
Hi,

We have implemented a new global buckling constraint feature in V7.1 (currently in beta). Attached is a description of this new feature.

1) The location of the buckling mode is automatically detected within a display set based on the grid displacements.
2) Required stiffness factors are applied per mode, per component based the relative grid displacement.
3) All modes shapes can be displayed in the FEM viewer.
4) Frequency constraints have been added as well. The algorithm is identical to the one used for global buckling.

We may be able to distribute a beta version of V7.1 to you. I will contact you offline for more details.

Thanks,
Ryan

mraedel:
Sounds promising.

I am looking forward to hear from you.

mraedel:
Hi, I now use HyperSizer 7.1.43 which should support global buckling and modal analysis. So, I used HyperFEA, created a FEA Constraints for buckling and eigenfrequency on a displayset containing the whole model. I additionally use displacement constraints.

When I start HyperFEA, everything works. The displacement constraints act as expected. But unfortunately, in the Iteration Report Constraints tab I see, that the actual eigenvalue for buckling and the actual eigenfrequency of the iteration are zero.

Does this mean no buckling and modal analysis was performed? I have no real idea how to tell HyperSizer to perform a global buckling anaylsis in ANSYS.

I re-read the attached word-file from your previous answer and read the sentence "The project must include the run deck with the buckling solution. Modal grid displacements must be exported to the relevant FEA results file."

Does this mean I have to provide buckling results in the initial ANSYS rst-file at import? How do I tell ANSYS to write these buckling results in the same rst-file as the static solution?

The import of load sets is described here. When I try to use


--- Code: ---/SOLU
LSSOLVE,101      ! Static solution with PSTRES,ON
LSSOLVE,201      ! Buckling
FINISH

--- End code ---

I get an error in ANSYS:


--- Code: ---The analysis type must not be changed after the first load step.  For a
new analysis, enter the FINISH command now and reenter using the
/SOLUTION command.

--- End code ---

But if I use


--- Code: ---/SOLU
LSSOLVE,101      ! Static solution with PSTRES,ON
FINISH
/SOLU
LSSOLVE,201      ! Buckling
FINISH

--- End code ---

the calculation is done, but the rst-file of the static solution is overriden by the buckling solution and I can not import the reaction loads for the static load case in HyperSizer.

Is there a simple exemplary CDB-File with load step data or an APDL file to show the process?

Ryan:
We've seen this too. To the best of our knowledge, you can't have an ANSYS result file (RST) with both static (perturbation) and buckling results. This appears to be a limitation of the RST format in ANSYS.

The workaround would be to make separate run decks  - one with static, and another with static + buckling. You can use include statements to share model, loads, and boundary condition data between the two run decks.

-Ryan

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