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Reference: ParaView Version 4.3.1<br>
<br>
I have two technical questions:<br>
<br>
(Q1) In the PV filter 'Gradient Of Unstructured Data Set' is the
"QCriterion" function, the Q-Criterion defined by J. C. R. Hunt, A.
Wray, and P. Moin (1988) "Eddies, stream, and convergence zones in
turbulent flows," Center for Turbulence Research Report CTR-S88, and
referenced by G. Haller in "<i>An objective definition of a vortex</i>,"
J. Fluid Mech. (2005), vol. 525, pp.1–26?<br>
<br>
(Answer to Q1) Courtesy of Don Simons of Egility Corp., Yes, the
formula being<br>
Q=-0.5*(Vx,x*Vx,x + Vy,y*Vy,y + Vz,z*Vz,z) - (Vx,y*Vy,x + Vx,z*Vz,x
+ Vy,z*Vz,y)<br>
<br>
(Q2) In the PV filter 'Calculator' what is the formula used by the
"mag" function to calculate mag(<b>S</b>) where <b>S</b> is a
symmetric 2nd-order tensor? Using matrix notation, the tensor <b>S</b>
would have the following components:<br>
<br>
---------------<br>
| Sxx Sxy Sxz |<br>
| Sxy Syy Syz |<br>
| Sxz Syz Szz |<br>
---------------<br>
<br>
(Answer to Q2) The PV formula for mag(<b>S</b>) is the square root
of the sum of the squares of the 6-tuple (Sxx, Syy, Szz, Sxy, Sxz,
Syz). <br>
<br>
For consistency with a three-component vector, I would have expected
it to be the 6-tuple (Sxx, Syy, Szz, 2Sxy, 2Sxz, 2Syz)?<br>
<br>
<br>
Samuel W Key<br>
FMA Development, LLC<br>
1005 39th Ave NE<br>
Great Falls, Montana 59404<br>
USA
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