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Re: [Question #679411]: About cell.trsf and cell.velGrad

To: yade-users@xxxxxxxxxxxxxxxxxxx
From: Bruno Chareyre <question679411@xxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 12 Apr 2019 15:13:17 -0000
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Question #679411 on Yade changed:
https://answers.launchpad.net/yade/+question/679411

    Status: Open => Answered

Bruno Chareyre proposed the following answer:
That's actually a straighforward case since it's irrotational.

In you example with trsf[2,2]=0.9998  the true target strain is not -0.0002. You are using the small strain (or "engineering" strain) approximation, and you suffer the consequences.
The natural strain is not assuming smallness, it is log(trsf[2,2]=0.9998)=-0.00020002.
As you can see the 2e-8 difference is exactly the missing amount in your final trsf.

If you need to reach 0.9998 in N steps then the strain rate should be
log(0.9998)/(N*O.dt).

Bruno

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