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
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
I ran into problems. Static solution using octave solving Cu=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 calculix–> 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 don’t get the mass of my system (which should be the case if I am
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 …
Any help or suggestion would be highly appreciated!
Thanks a lot in adance,
PS: Thinking about the sum of the Mass-Matrix a bit more, it should be 3*Mass_of_Body for a 3D-problem… which came out correctly.