Damping in Linear Transient Analysis
Hello all,
I have a question about damping definition in linear transient analysis, either direct or modal.
In OptiStruct tutorial OS-T 1315 Modal Transient Dynamic Analysis, a 2% damping ratio is defined in TABDMP1 table with 0.02% between 0Hz and upper EIGRL value 1000Hz.
But in OS-T 1310 Direct Transient Dynamic Analysis, PARAM,G = 0.2 with PARAM,W3 = 300 are used. I do not understand the last case (what are these values?) and the link with 0.02 value in Modal Transient analysis. More precisely, why G is 0.2 and not 0.02, and why W3 (which if I am right is supposed to be a frequency??) is 300?
In addition, I have read in OptiStruct help that TABDMP1 refered in SDAMPING subcase in a Loadstep could combined with PARAm,KDAMP,-1 to be equivalent to PARAM,G.
All those different information make me a bit confused. Is it also possible to use PARAM,G in Modal Transient ?
Naturally, I would have done the same thing as Modal Transient in any case : a TABDMP1 table with 0.02 CRIT value called in SDAMPING Loadstpe subcase. But if I try to use PARAM,G I get the same thing as if I did not refer SDAMPING, so without damping definition.
Can someone clarify correct and possible setups for damping definition in (Modal) Transient Analysis?
Thank you!
Answers
-
0
-
Altair Forum User said:
Does this equation in the documentation help you?
Well, thanks @Adriano A. Koga but I had read that help page before asking, and it doesn't help as it is written 'Frequency of interest in radians per unit time (PARAM,
W3) for the conversion of overall structural damping into equivalent viscous damping.' It doesn't say what this frequency is supposed to be, or why the 0.02 damping ratio in TABDMP1 is replaced by 0.2 with W3=300 in the tutorials I quoted./emoticons/default_unsure.png' title=':unsure:' />
0
Altair Employee