displacement frequency is exploded

[Jee-Bee]

I have a question regarding the units after creating the frequency calculation and the related displacement factor.

I have a model added below. Where i create a Frequency calculation combined with static.
so just a static calculation and add the code below after the *END STEP of static to create to eignemodes calculation.

Code: Select all

*STEP, PERTURBATION
*FREQUENCY
10
*END STEP

my problem is that when plotting the eigenmodes plots the max displacement = 360 or so mm(??). while the max distance = 126.25 mm. So it breaks everything... when showing even at displacement factor 1.

2019-07-25 14_00_56-FreeCAD 0.19.png (41.49 KiB) Viewed 1187 times

I'm not sure but i would say that the resulting values aren't mm there is no input energy added so also no magnitude...
Would it be possible to scale this max value so 'large' displacements can shown normal??

[Jee-Bee]

No others who are having the same issue? (or maybe iam very bad at explaning my problem... )

[fandaL]

Forum search gives a related discussion here https://forum.freecadweb.org/viewtopic. ... 8&start=10 There is the python code for scaling <1 https://forum.freecadweb.org/viewtopic. ... 10#p289519

So a way around could be to use Pipeline/Warp filter to display deformed shape with arbitrary scale.

[Jee-Bee]

that's a pita that a workaround is needed. i try to create a pipeline...

Still i don't understand where the extremly high "displacement" values of frequency analysis come from...

[fandaL]

Still i don't understand where the extremly high "displacement" values of frequency analysis come from...

The theory behind frequency analysis gives only the shape and frequency, not information about amplitude, so displacements you see are not real. Calculix gives output which is somehow normalized (mass normalized so that “displacements” fulfill equation uMu=1 where u is eigenvector, M is mass matrix). For real displacements one would need to run some kind of dynamic analysis which is more complicated.

[Jee-Bee]

thanks