# how to choose the unbalanced force ratio

hi,

I'm wondering if someone knows how to determine the Unbalnaced force ratio? Are there any criteria that we can refer to or some paper I can read?

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Bruno Chareyre
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2019-05-06
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2019-05-06
2019-05-06
 Jérôme Duriez (jduriez) said on 2019-05-06: #1

Hi,

You mean "how to choose the threshold value (for quasistatic conditions to happen)" ?

As for me, I usually aim for values around 0.5 -- 1 %, and I'm quite sure this always ensures quasi staticity for my simulations (which is kind of what the doc says).
I mentioned this choice of threshold e.g. in https://onlinelibrary.wiley.com/doi/full/10.1002/nag.2774, but there should be many other examples.

There also are some examples and counter-examples in my PhD thesis, e.g. Fig. 2.25 and 2.26. It's for interface tests, being able to read French might help..

 nobody (nobody01) said on 2019-05-06: #2

Hi,
Yeah, I mean "how to choose the threshold value".

do we have some criteria for all the simulations? or it depends on different simulations?

thanks

 Bruno Chareyre (bruno-chareyre) said on 2019-05-06: #3

Hi,
"unbF" is just an indication.
Everything is problem dependent, and the first questions are more "which value are you interested in?" and "which tolerance do you have on the determination of that value". On this basis you may find which unbF is ok.
Bruno

 nobody (nobody01) said on 2019-05-06: #4

Hi,
So we don't have something like the inertial number to determine the "unbF"

thanks

 Bruno Chareyre (bruno-chareyre) said on 2019-05-06: #5

Inertial number is just like unbF, it's just an indication (except that Iv is defined from input, unbF is defined from output and in that sense it's closer to what you need).
It doesn't tell you in advance, quantitatively, how much non-static perturbation you get in an arbitrary problem.
Also, Iv is defined only in homogeneous situations.
Bruno

 nobody (nobody01) said on 2019-05-06: #6

Thanks Bruno Chareyre, that solved my question.