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by HarryvL
Sun Jul 14, 2019 7:24 am
Forum: FEM
Topic: Buckling and Free Vibrations (without integrals or matrices)
Replies: 1
Views: 105

Buckling and Free Vibrations (without integrals or matrices)

An interesting challenge from Bernd (https://forum.freecadweb.org/viewtopic.php?f=18&t=37400&start=20#p319473) ... ... do you know some paper which explains all this without tons of integrals and matrix operations ... Attached an attempt at this for the interested reader. Buckling and Free Vibration...
by HarryvL
Tue Jul 09, 2019 8:15 pm
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

I can confirm this is the case. Analysis of a rigid column on a rotational spring shows that the frequency eigenvalue depends as follows on the vertical load F: (Omega_F) ^ 2= (1 - F/FE) * (Omega_0) ^ 2 where FE is the Euler buckling load of the column. So the natural frequency reduces to zero as t...
by HarryvL
Tue Jul 09, 2019 6:54 am
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

4) The only case I can imagine where we could hit a similar issue with FreeCAD is when we load a part or structure with forces that exceed the elastic buckling load (but I would need to check the math of such a case to be sure) I can confirm this is the case. Analysis of a rigid column on a rotatio...
by HarryvL
Mon Jul 08, 2019 11:43 pm
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

This is surprising and different from what I remember. I will look into it and compare to what I did for the bridge. great PS: yes the natural frequency in rad/s is the eigenvalue of the free vibration problem. than what is the column eigenvalue for? Do you know some paper which explains all this w...
by HarryvL
Mon Jul 08, 2019 11:18 am
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

This is surprising and different from what I remember. I will look into it and compare to what I did for the bridge. great PS: yes the natural frequency in rad/s is the eigenvalue of the free vibration problem. than what is the column eigenvalue for? Do you know some paper which explains all this w...
by HarryvL
Mon Jul 08, 2019 9:50 am
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

This is surprising and different from what I remember. I will look into it and compare to what I did for the bridge.

EDIT: the natural frequency in rad/s is the square root of the eigenvalue of the free vibration problem.

EDIT: see https://forum.freecadweb.org/viewtopic. ... 30#p319635
by HarryvL
Sat Jul 06, 2019 2:18 pm
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

bernd wrote:
Sat Jul 06, 2019 12:31 pm
HarryvL wrote:
Sat Jul 06, 2019 12:19 pm
I don’t understand. You have 5 values per line so the last one should be imaginary part in Hz as per my post.
no the number and four values ... see my screen from dat file !
EDIT: see https://forum.freecadweb.org/viewtopic. ... 30#p319635
by HarryvL
Sat Jul 06, 2019 2:04 pm
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

EDIT: see https://forum.freecadweb.org/viewtopic. ... 30#p319635
by HarryvL
Sat Jul 06, 2019 12:19 pm
Forum: FEM
Topic: extraction of negative eigenvalues
Replies: 34
Views: 753

Re: extraction of negative eigenvalues

- 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 Box_Mesh.dat.txt Screenshot_20190706_125...

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