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

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...

- Tue Jul 09, 2019 8:15 pm
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

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...

- Tue Jul 09, 2019 6:54 am
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

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...

- Mon Jul 08, 2019 11:43 pm
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

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...

- Mon Jul 08, 2019 11:18 am
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

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...

- Mon Jul 08, 2019 9:50 am
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

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

EDIT: the natural frequency in rad/s is the

EDIT: see https://forum.freecadweb.org/viewtopic. ... 30#p319635

- Sat Jul 06, 2019 2:18 pm
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

EDIT: see https://forum.freecadweb.org/viewtopic. ... 30#p319635

- Sat Jul 06, 2019 2:06 pm
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

- Sat Jul 06, 2019 2:04 pm
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

EDIT: see https://forum.freecadweb.org/viewtopic. ... 30#p319635

- Sat Jul 06, 2019 12:19 pm
- Forum: FEM
- Topic: extraction of negative eigenvalues
- Replies:
**34** - Views:
**753**

- 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...