Flexible body damping ratio

Hello,

I am trying to understand how the damping ratio is introduced to a flexible body in Adams. I understand that CRATIO acts as a percentage of the body's damping ratio but what I don't know is wether I should create a TABDMP card in the Nastran file when generating the MNF file or if the CRATIO statement does this exact same thing.

Thanks,

Josef K.

0 Jan Sotnik over 3 years ago

Hello Josef,

to apply modal damping (CRATIO) you do not have to create TABDMP card in bulk data file. The SDAMPING with TABDMP1 cards are used to define generalized damping which stores generalized damping matrix in MNF.

In fact one can define the "Damping Ratio" and "Generalized Damping" independently per flex body - see "Flex Body Modify" dialog box and one can also apply a combination of both. In case you have access to Knowledge Base articles have a look at this one and search for more:

GDAMP and MODAL damping in Adams

Hope it helps.

Greetings,

Jan
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0 Josef K. over 3 years ago

Hi Jan,

So if I understand this correctly, setting up CRATIO properly can allow me to avoid using the SDAMPING and TABDMP1 statements entirely, right?

e.g., Assuming I wanted a damping of 1% increasing to 2% from 0 to 100 Hz, I could either:

1) define the TABDMP1 statement when producing the MNF file and then enable GDAMP inside the flex body modify

or

2) define the CRATIO statement [STEP(FXFREQ, 0, 0.01, 100, 0.02) in this case] in Adams,

meaning tha combination of both is unecessary.

Thanks in advance,

Josef K.
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0 Jan Sotnik over 3 years ago

Hi Josef,

yes, your understanding is right.

Greetings,

Jan
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