Help: Producing a Stiffness Matrix

General Questions
1

I’m a relative novice to FE and new to Prepomax and Calculix.

In my day job, I’m a design engineer. My present customer is having some gears analysed and the gear specialists want a stiffness matrix for the gearbox housings to import into their analysis. They have a section in their help guide “Importing a Nastran Triangle format stiffness matrix”.

Can Prepomax produce and export a Nastran Triangle format stiffness matrix? If so, could someone guide me through the process, or point me towards documentation that would help me to produce what I want?

2

Check this thread and maybe other from that guy: To output element stiffness matrix to a result file - CalculiX (official versions are on www.calculix.de, the official GitHub repository is at https://github.com/Dhondtguido/CalculiX).

Basically, there are two options:

  • *FREQUENCY, SOLVER=MATRIXSTORAGE
  • substructure generation: a few keywords to create so-called substructures (superelements) - extract matrices while leaving some DOFs available for use in further linear analysis

Both require keyword edits (there’s a built-in Keyword Editor in PrePoMax or you can export input files and edit them manually) because they aren’t supported in GUI. Check the CalculiX User’s Manual for more details regarding them: https://www.dhondt.de/ccx_2.22.pdf

I would focus on the first option for now, it should be sufficient. The only question is about the right format. Of course, it won’t be the Nastran format exactly but once you have the stiffness matrix extracted, you might be able to convert it to the desired format.

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