Hi All,

being new to this platform, I start with a short intro: working in the field of FEA for quite some time (personal experience primarily with MARC & ABAQUS, a bit of NASTRAN,a bit of ANSYS), I am driving a small project just out of personal interest: I would like to realize an open-source workflow where a reduced FEA model is implemented into an Modelica-Model (FMU/FMI) for system

modeling.

My current approach:

- FEA-Sover Calculix, dumps Mass & Stiffness Matrix
- pymor reduces Full-Order Model (FEA) to reduced Order Model (a bit away from Craigh-Bampton)
- Modelica SDK implements reduced model (not decided yet because I am stuck @ topic 2)

I used a very simple beam model as a pilot (Nextcloud).

Modal result look reasonable (1st Eigenfrequency 186 Hz), static solution matches closed form solution sufficiently.

After exporting using

*FREQUENCY, SOLVER=MATRIXSTORAGE,
I ran into problems. Static solution using octave solving C*u=f, checking for the node I am interested,

delivered Calculix results, seems OK.

Some helping hands from the Pymor discussion group suggested that the Mass matrix might be wrong. After some clean up ( the converter calculixâ€“> MatrixMarket in the link above is still not correct, I used different approach), I am still getting strange results.

For example: I summed all elements of the mass matrix (of course considering the symmetry and

the storage of Calculix), I donâ€™t get the mass of my system (which should be the case if I am

not mistakenâ€¦).

I checked the source code (matrixstorage.c) which looks very reasonable (M & C dump consistent),

so I am a bit stuck, probably hunting for (but not seeing) the obvious, trivial mistake â€¦

Any help or suggestion would be highly appreciated!

Thanks a lot in adance,

Claus

PS: Thinking about the sum of the Mass-Matrix a bit more, it should be 3*Mass_of_Body for a 3D-problemâ€¦ which came out correctly.