Learning Forum

[shathabhisha.bhargav]

Hello,
I want to find peak stresses of the model at 30g, for the range 2500Hz to 2700Hz. So when I select equivalent stress and max principal stress in the solution section, I get the results of the stresses for the model, but in the details section--> in the defintion tab, there's a option to define by where I set it to "maximum over frequency" and Amplitude to "Yes", when I do this I get different stress values for Max principal stress as well as von-mises stress. What is the difference between these two results? Are the first results were scaled down by 0,7071(RMS value)? Are the stress values which I get when I select from "maximum over frequency" and Amplitude "Yes" are the peak stress at the resonance for the above mentioned range?

[dlooman]

Your first set of results may just be the "Real" results.  A harmonic analysis produces a real and imaginary result and the maximum usually occurs at some phase angle to the real solution.  The "Amplitude" result is the SRSS of the real and imaginary solution and so is probably greater than your first result.  There's no .7071 scaling being done.  

[shathabhisha.bhargav]

Thanks for the reply, I understood as this way, Please correct me if I am wrong.
-->The intial stress results are RMS(root mean square) where RMS=Amplitude /√2,
Here the solver treats the input value as RMS, consequently the response(stresses, displacement) will also be scaled down by 1/√2, So when I select both option "maximum over frequency" and and Amplitude as "YES", this generally does is, it gives peak stresses or maximum response values that occur due to harmonic loading. This is typically required for fatigue or failure analysis, as components experience peak loads in real- world scenarios. If we select amplitude "NO", solver uses RMS values, here the stress values are lower, which represents the effective value over time(average power in dynamic systems)

[dlooman]

No, Ansys never reports the RMS value.  By default it reports the real results, which are the results at phase angle zero.  Amplitude is SRSS(Real, Imag).   Another postprocessing technique is Maximum over phase angle.  

[shathabhisha.bhargav]

Understood, Thank you. So to know the peak responses at resonance(in my case) it is better to use SRSS value i.e. Amplitude "Yes"

[dlooman]

Yes.  At resonance the imaginary result is the largest so Amplitude should capture that.