Learning Forum

[Samuele Luigetti]

Good morning everybody

I have a problem with harmonic response linked to modal. The problem is that i have tot. forces in a certain direction acting on a structure and the output of the harmonic response (so the deformation that occurs at the peak in the frequency response in the same direction) does not correspond to what is expected. So i did several tests and i found out that the deformation expected occurs only when i put only a part of the forces (for example: i have 12 several harmonic loads: the simulation it's right with only 4 harmonic loads). This is strange because the shape of the deformation should be the same (or similar) if the harmonic loads have the same direction also if are in a different number. Hope that someone can help me, thanks!

[Claudio Pedrazzi]

Hi Samuele

are you speaking of a comparison between an experiment (measure, reality) and the FEM-simulation wiht ANSYS? 

In this case, how did you define the damping? In my experience, the damping is the real "unknown" and it has a lot of influence on the results of an harmonic analysis.

[Samuele Luigetti]

No, i'm talking about only fem simulations with workbench

[Claudio Pedrazzi]

ok, thanks. 

 

>>... to what is expected. So i did several tests and i found out that the deformation expected occurs only when i put only ...

Please define "deformation expected".

Expected from what? a known analytical solution? Anyway have a look at the damping nevertheless, it is an important input.  

[Samuele Luigetti]

Expected since the forces that acting on the structure and the solution of the linked modal, so the expected is not based on analytical solution or sperimental.

For the damping i set 2% because of the impossibility to know. Anyway i can try to change this and see what change.