FEM - Dynamic Loads?

About the development of the FEM module/workbench.

Moderator: bernd

JensElmo
Posts: 5
Joined: Fri Feb 16, 2018 9:16 am

FEM - Dynamic Loads?

Postby JensElmo » Fri May 18, 2018 8:29 am

I have a project where I have essentially a mechanical hammer hitting object with a down force of 160kN in a percussion rate of 32 Hz.
I am not able to find out how in the FEM module to apply a dynamic load, if that is even possible in FreeCAD.
So I was hoping somebody could help me, or direct me to a tutorial about dynamic loads.




FreeCAD Info
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.13387 (Git)
Build type: Release
Branch: master
Hash: c5f4079252b11e3c54cd603be7d3697fa9f9d922
Python version: 2.7.14
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.1.0
Locale: Danish/Denmark (da_DK)
Jee-Bee
Posts: 971
Joined: Tue Jun 16, 2015 10:32 am
Location: Netherlands

Re: FEM - Dynamic Loads?

Postby Jee-Bee » Fri May 18, 2018 11:33 am

You have to modify you're input file of calculix.
you need at least add the *AMPLITUDE parameter.
see for a bit more information http://www.feacluster.com/CalculiX/ccx_ ... de202.html
I'm not sure what type of analysis you need. just start with *STATIC and try out..
User avatar
HarryvL
Posts: 275
Joined: Sat Jan 06, 2018 7:38 pm

Re: FEM - Dynamic Loads?

Postby HarryvL » Fri May 18, 2018 1:57 pm

@Jee-Bee, the simplest analysis type that captures steady state dynamic response is "Steady State Dynamic Analysis, as I use and describe here:

https://forum.freecadweb.org/viewtopic. ... 50#p232309

However this assumes a sinusoidal periodic load. If you have a different periodic load then you would need Fourier analysis to write this as a sum of periodic loads. I believe there is an option for that too in CCX. However, I would first try to use the simplest option (above) and see if you can make that work.
User avatar
HarryvL
Posts: 275
Joined: Sat Jan 06, 2018 7:38 pm

Re: FEM - Dynamic Loads?

Postby HarryvL » Fri May 18, 2018 2:05 pm

I just checked the manual. CCX can indeed decompose a general periodic load into sinusoidal (harmonic) components using Fourier transform. The only additional thing you need to do (in addition to what I describe above and in my bridge post) is to add HARMONIC=NO to the *STEADY STATE DYNAMICS card and describe one period of the load in the *AMPLITUDE card. It will produce similar results as in my post, so please take care with the post processing. I would be interested to see your results.
Jee-Bee
Posts: 971
Joined: Tue Jun 16, 2015 10:32 am
Location: Netherlands

Re: FEM - Dynamic Loads?

Postby Jee-Bee » Fri May 18, 2018 3:12 pm

Sorry @HarryvL i just read sometimes parts of of the CCX documentations but it takes time to gain some experience