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Rate of strain in a fluid

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Old   December 12, 2003, 08:48
Default Rate of strain in a fluid
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I am trying to determine the value of strain in a fluid. A literature review leads me to:

Sij = 1/2 (duj/dxi + dui/dxj)

Some papers have

|S| = sqrt(2 * Sij Sij)

whilst others have

|S| = sqrt (Sij Sij)

Can anyone tell me which is correct.


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Old   December 12, 2003, 12:33
Default Re: Rate of strain in a fluid
vasanth allampalli
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The first one seems familiar and correct
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Old   December 15, 2003, 07:54
Default Re: Rate of strain in a fluid
Jonas Bredberg
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The first formula gives you the rate of strain as commonly defined, in tensor notation and hence with direction. I've seen, as you, both the other two defintions for the total strain. I would prefer people to use the one without 2.
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Old   January 21, 2004, 13:09
Default Re: Rate of strain in a fluid
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The first one is the strain rate tensor (3x3 matrix) while the latter is the magnitude of the strain rate tensor (a scalar value). Both are correct depending on what you want to evaluate.
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