|June 15, 2007, 09:37||
Hi FOAMers, I would like to
Join Date: Mar 2009
Posts: 24Rep Power: 10
I would like to have your opinion about the following problem:
- the strain tensor is defined as
S = 2 * symm(grad(U)) = grad(U) + grad(U)^T (1)
- and, according to the linear algebra, its magnitude is
|S| = sqrt(.5 * (S_ij * S_ij)) (2)
- now, if I let OpenFOAM to write out both the U gradients and S
S = mag(2*symm(fvc:grad(U))) (3)
I see that values coming from (3) and (2) (calculated manually) are different.
I had a look to the vectorSpace class and what I can understand (with my little C++ knowledge), is that the magnitude of a tensor S is given by
|S| = sqrt(Sij * Sij) (4)
which differs from Eq. (2). Additionally, a manual check with the help of Eq.(4) does not return what is given by OF (Eq. (3)) and there is not any constant factor between their values...
What am I missing?
Thanks a lot,
|August 7, 2011, 03:02||
Join Date: Aug 2009
Location: Wiesbaden, Germany
Posts: 241Rep Power: 10
strain rate Tensor is defined by
S:=1/2 [ grad(U)+gard(U)^T]
Try it and give me respond if it's worked.
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