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<div class="moz-cite-prefix">Hi Andy,<br>
<br>
unfortunately my comparison values (correct lambda2) does not have
an results in between to compare with. Regarding the gradients i
am sure they are ok. For this dataset i calculated other stuff
based on the gradients and thats ok. Maybe the error is in the
syntax or the usage of the eigenvalues-function - will check there
...<br>
<br>
Stefan <br>
</div>
<blockquote type="cite"
cite="mid:CAMaOp+Ha7Q71iOjzKmjO5X++Fg4xwQS9z0bjqbNAdD_TJmiW3w@mail.gmail.com">
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<div dir="ltr">Hi,
<div><br>
</div>
<div>Maybe compute each portion manually and check that against
the correct values. Also, verifying the gradient calculation
is correct is another thing to look at. If the grid isn't
specified properly then the gradient operation will likely be
wrong.</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Jun 9, 2017 at 8:46 AM, Stefan
Melber <span dir="ltr"><<a
href="mailto:Stefan.Melber@dlr.de" target="_blank"
moz-do-not-send="true">Stefan.Melber@dlr.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div> Hi,<br>
<br>
<br>
for vortex-detection i (tried) to calculate the
lambda2-criterion (see e.g. <a
class="m_6725794015711734747moz-txt-link-freetext"
href="https://en.wikipedia.org/wiki/Lambda2_method"
target="_blank" moz-do-not-send="true">https://en.wikipedia.org/wiki/<wbr>Lambda2_method</a>)
with ParaView. The way of calculation is based on this
link <a
class="m_6725794015711734747moz-txt-link-freetext"
href="http://www.iesensor.com/blog/2016/01/24/using-paraview-to-visualise-vorticity-lambda2-vorticity-q-criterion/"
target="_blank" moz-do-not-send="true">http://www.iesensor.com/blog/<wbr>2016/01/24/using-paraview-to-<wbr>visualise-vorticity-lambda2-<wbr>vorticity-q-criterion/</a>.<br>
<br>
However - the results are a kind of "wrong" - see attached
pictures: l2_solver.png shows what the flow solver writes
out for lambda2, l2_paraview.png shows what calculated
with the algorithm below.<br>
<br>
Calculation of lambda2:<br>
<br>
<tt>D = Gradients = [d_ij]</tt><tt><br>
</tt><tt>S = strain(Vel)</tt><tt><br>
</tt><tt><br>
</tt><tt>S = (D + D^T)/2</tt><tt><br>
</tt><tt>Omega = (D - D^T)/2</tt><tt><br>
</tt><tt><br>
</tt><tt>lambda = EigenValue_of(S^2 + Omega^2) </tt><tt><br>
</tt><tt> = EigenValue_of(S^2 + (D - S)^2) </tt><tt><br>
</tt><tt> = EigenValue_of(S^2 + (Gradients -
strain(vel))^2) </tt><tt><br>
</tt><tt> </tt><tt><br>
</tt><tt>lambda2 = lambda_Y</tt><tt><br>
</tt><br>
and in ParaView this mean<br>
<br>
<tt>o Vector of velocity with
"Calculator".................: Vel =
iHat*x_velocity+jHat*y_<wbr>velocity+kHat*z_velocity</tt><tt><br>
</tt><tt>o Gradients of Vel with "<wbr>GradientOfUnstructuredDataSet"<wbr>:
switch on "compute gradient" and name it "Gradients"</tt><tt><br>
</tt><tt>o Calculate lambda with
"PythonCalculator"............<wbr>.: lambda =
eigenvalue(strain(Vel)**2+(<wbr>Gradients -
strain(Vel))**2)</tt><tt><br>
</tt><tt>o Caluclate lambda2 with
Calculator....................<wbr>: lambda2 = lambda_Y</tt><tt><br>
</tt><br>
<br>
<br>
Does anyone see the error why the calculation of lambda2
with ParaView does not work?<br>
<br>
Remark: i contacted the author of the blog above already -
seems he never tested his calculation and has no idea what
is "wrong".<br>
<br>
Stefan<br>
<br>
<br>
<br>
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