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how to choose the unbalanced force ratio

Asked by ytang

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?

thanks in advance.

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Bruno Chareyre
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Jérôme Duriez (jduriez) said : 		#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..

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ytang (ytang116) said : 		#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

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Bruno Chareyre (bruno-chareyre) said : 		#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

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ytang (ytang116) said : 		#4

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

thanks

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Best Bruno Chareyre (bruno-chareyre) said : 		#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

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ytang (ytang116) said : 		#6

Thanks Bruno Chareyre, that solved my question.