Random Fatigue Analysis

Altair Forum User

Hello guys,

I'm trying to do a Random fatigue analysis thanks to Optistruct. So first of all, I know that 2017 version has its own module which does this kind of analysis, and I already did it. 
I'm now trying to compare Optistruct results with a VBA code I did.
So here are the step I did:

- FRF and Random Subcases (with RANDPS, TABLED1 etc)
- I ask for STRESS PSDF .Peak files for X to Z1, X to Z2, Y to Z1, Y to Z2, XY to Z1 and XY to Z2
 Here, I can already see the number of positive crossing (which allow me to calculate life). First Question, do I have to divide this number by 2PI?

My second question is, is it okay to create a derivated results on Hyperview, which does : RMS VELOCITY / (2*PI RMS DISPLACEMENT) in order to obtain the number of positive zero crossing directly on HyperView?
This whole zero crossing things is kind of getting me crazy, a lot of people use it but I do'nt really understand how it works.
(By the way, I can give you the files I have on my simple model if it is needed)


Thanks for your answers!

Altair Forum User

Hi,

 

Are you looking at equivalent PSD Stress?

 

Please do share the files 

Altair Forum User

Hi,

Please forgive me I'm kind of new to this and I don't really know how to be sure to look at equivalent PSD stress.

here are My files, please tell me if anything is correct. By the way I did one different subcase for direction.

NB : I limited the study to one element, ID = 14 (the one taking most damage according to Optistruct).
 

Unable to find an attachment - read this blog

Altair Forum User

@francois.B

 

Thank you for sharing the files. I will update you soon /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20'> 

Altair Forum User

Okay Thank you a lot !
Please ask me if you need anything else.