I have been using FreeCAD for about 2 weeks.
Suggestion:
My suggestion is that a negative value can be specified for the "Eigenmode Low Limit"
Justification:
I have been performing "Free-Free" Frequency Analyses and I have noticed that not all the Rigid Body Modes are displayed under the Calculix frequency output. (The Rigid Body Modes are those with eigenvalues close to 0.0.)
The modes that are not displayed are those with small negative eigenvalues, of the same magnitude as the other small values, output from Calculix within FreeCAD:
E I G E N V A L U E O U T P U T
MODE NO EIGENVALUE FREQUENCY
REAL PART IMAGINARY PART
(RAD/TIME) (CYCLES/TIME (RAD/TIME)
1 -0.9206131E-05 0.0000000E+00 0.0000000E+00 0.3034161E-02
2 0.4278982E-05 0.2068570E-02 0.3292231E-03 0.0000000E+00
3 0.3131142E-04 0.5595660E-02 0.8905770E-03 0.0000000E+00
4 0.4225360E-04 0.6500277E-02 0.1034551E-02 0.0000000E+00
5 0.4730425E-04 0.6877809E-02 0.1094637E-02 0.0000000E+00
6 0.6699469E-04 0.8185029E-02 0.1302688E-02 0.0000000E+00
7 0.1543087E+09 0.1242211E+05 0.1977040E+04 0.0000000E+00
8 0.2150798E+09 0.1466560E+05 0.2334103E+04 0.0000000E+00
9 0.3530977E+09 0.1879089E+05 0.2990664E+04 0.0000000E+00
10 0.3532363E+09 0.1879458E+05 0.2991251E+04 0.0000000E+00
This output was achieved by modifying the "FREQUENCY" input data in the *.inp file and rerunning.
The small negative value is due to roundoff error. The "jump" between the eigenvalues of the 6th and 7th modes is typical of a good model.
The analysis of "Free-Free" models is an important step in the validation of FEM models. If the model has less than 6 rigid body modes then it implies that there is some sort of constraint within the model.
mac