extraction of negative eigenvalues

[UR_]

the reader code never changed over the years

phpBB [video]

[PrzemoF]

Just tried a frequency analysis by modifying cantilever3D example from start page.

Got mode 1 to 15.

If I select result object e.g. "CalculiX_frequency_mode_1_results", I see in properties:


Screenshot 001.png


But same values for all modes

Where is the beaf?

Check if you see the results in the file produced by CalculiX. If it's there then the reader is broken, but I doubt it - it worked since it was added to the FreeCAD code. Another option is change of formatting by CalculiX, but that's unlikely. Post the model, so someone can check it.

P.S. I never dreamt that the reader code might survive that long without modifications

[UR_]

Post the model, so someone can check it.

FemCalculixCantilever3D.FCStd

(620.53 KiB) Downloaded 4 times

Box_Mesh.dat.zip

(2.13 KiB) Downloaded 6 times

[bernd]

I can confirm the problem for 0.19 Just open FEM 3D example change from static to frequancy analysis.

Ahh it works in 0.18.2 ... which means I may am the culprit in one of the lots of code refactoring commits ... I will have a look ...

screen.jpg (176.32 KiB) Viewed 198 times

[bernd]

my vault ...

I deleted this line https://github.com/FreeCAD/FreeCAD/blob ... em.py#L284 I will have a look how to fix this.

[bernd]

git commit 20b78fc fixes the eigenmode reading. Back to the origin question ...

Is the eigenmode we gone read from dat file the right one ??? https://github.com/FreeCAD/FreeCAD/blob ... py#L94-L95

[HarryvL]

Judging from the table in the first post the entries in the frequency line are as follows:

Code: Select all

<mode number> <real part of frequency in rad/s> <real part of frequency in Hz> <imaginary part of frequency in rad/s> <imaginary part of frequency in Hz>

EDIT: this is not correct. see: https://forum.freecadweb.org/viewtopic. ... 30#p319635

[HarryvL]

A practical example of a natural frequency analysis where the imaginary part of the response needs to be considered:

https://forum.freecadweb.org/viewtopic. ... 50#p232717

EDIT: this relates to imaginary response modes and not to imaginary frequencies

[bernd]

- start FreeCAD
- load FEM 3D example
- change to analysis type frequency
- change from first 15 to first 8 frequencies
- delete constraint fixed and constraint force
- run analyisis
- the imaginary part in Hz is missing
- screen and file attached

test.FCStd

(330.26 KiB) Downloaded 3 times

Box_Mesh.dat.txt

(3.07 KiB) Downloaded 3 times

Screenshot_20190706_125522.png (58.25 KiB) Viewed 85 times

[bernd]

but I can the rad/Time use as well ... https://en.wikipedia.org/wiki/Radian_per_second just use /2pi ...