Learning Forum

[kshitij87]

Hello,

I want to perform a harmonic response simulation on a part for a specific duration of time. It is supposed to represent a vibration shaker test. The test conditions have been listed below:

Acceleration: 10m/s^2 (vertical direction)

Frequency: 7-50 Hz (at steps of 1Hz)

Total time for the test: 15 minutes (this is where I am stuck)

I know how to set up and run a harmonic response simulation with the acceleration conditions stated above, but can't figure out how to specify the time that the simulation must run for. Should I use the fatigue result and specify the time in that?

Also, should I look into transient structural for this problem?

Any help is appreciated.

Thank you.

-Kshitij

[Erik Kostson]

Hello

That is correct - harmonic analysis is in the frequency domain (not in time domain like a transient).

Time can come in as you said if one uses the fatigue tool in a harmonic analysis - that will give how many seconds the component can run at the excitation frequency before it fails.

This discussion might be useful if you look at the fatigue tool inside a harmonic response.



Finally one would not run transient for 15 minutes - since the system is in a steady state vibration harmonic is the analysis one could use.

We have courses on the subject which are useful:

All the best
Erik

[kshitij87]

Thanks a lot for the answer Erik, that discussion you linked was very helpful.
I will try using the fatigue tool to see how my model behaves.
I Just wanted to ask one more thing, is there a way in which I can specify the time for the simulation and see how my part performs?
Because my objective with the simulation is to model a real life vibration test that is run on battery packs to check for multiple failures. I can use a similar approach that is in the above linked discussion, but my concern is I don't want to design a part that has a life of 15 minutes. Rather, I want to see how it performs under 15 minutes of those loading conditions.
Regards Kshitij

[Erik Kostson]

No worries.
The term how it performs is very wage - you say multiple failures, but the most important thing that we can model is typically fatigue failure - for that use the fatigue tool.

The part will just vibrate at the excitation frequency during 15 minutes, so that is all that will happen, and this is just a steady state vibration, which we then model with a harmonic response.

So there is no need to run a transient analysis for 15 minutes :), that does not need to be run.

With the fatigue tool under the excitation you have and at a certain driving frequency it will tell you what the life is (it does not have to be 15 min, it can be 1 sec if the loads are high).

If we run for 15 minutes transient you will just see a steady state oscillation at the driving frequency - which is the same as the harmonic response at that frequency, but of course we do not need to run something for 15 minutes which can take a very long time. That is why harmonic is so good for these type of vibration tests.

See the course for more info please and the help manual structural analysis guide:
4.1. Uses for Harmonic Analysis
5 , Transient analysis

All the best

[kshitij87]

Thanks a lot for your help Erik. I will go through the course material and the guide and see what I can do. Regards Kshitij