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Convergence criteria (II)

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Old   August 21, 2009, 19:55
Default Convergence criteria (II)
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Daniel LLanes
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Hi everybody:

Shall i consider a fluctuation between two constant (approximately) values as a convergence (in the semi-value of the fluctuation between peak and valley) without assuming a great mistake?

Thx in advance!!
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Old   August 22, 2009, 05:09
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Giuki Cael
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That depends on the convergence history and the amplitude of the convergence I would say. It depends which residual you are considering, maybe you could check the contours and see if somewhere an irregularity occurs, trying to adapt the mesh at those spots and see whether you still have fluctuations. Also you might check the skewness of your mesh...
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Old   August 22, 2009, 06:27
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Daniel LLanes
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Its fluctuating around its third-fourth significative number, whose order is 10x^-3. Enough for my Cl, Cd and Cm (i think...)

Ty m8!!
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Old   August 22, 2009, 06:32
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Giuki Cael
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Is it the residual which is fluctuating or your Cl, Cd you are monitoring?
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Old   August 22, 2009, 19:40
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Daniel LLanes
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Here is an example of the residuals. Almost constant, as you can see... Fluctuation of Cd, Cl and Cm is what expected (anything but weird ), peak-valley-peak-valley-peak-valley and so on...

Thank you m8!!


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Old   August 22, 2009, 21:41
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In my experience residuals on the order of 1e-5 are small enough to consider it converged. I would consider the case converged in your case, assuming the amplitude of the oscillations aren't too large.

That said, I've seen residuals less than 1e-5 for Cl for a circulation-control airfoil and yet the magnitude of oscillations for Cl were on the order of 1 (for an airfoil with an expected Cl of around 6.) In that case, the problem turned out to be three-fold: highly skewed cells in areas of high gradients, too large of cells in these areas, and large area changes. Have you tried grid adaption based on gradients?

Another thing to check would be the under-relaxation factors and courant number. Try increasing all of those to see if it either causes divergence or convergence.
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Old   August 23, 2009, 06:13
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Daniel LLanes
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Ty m8s, this has been (is being) useful for me

Cheers!!
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Old   August 23, 2009, 20:28
Default Vibrational Analysis
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Sri
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Hello Everyone

Could any one please help me with vibrational Analysis.

I am carrying Vibrational Analysis on a Fuel Rail, if i want to add mass of the fuel during Modal analysis, how can i do ??

Please help me out.

Last edited by csri07; August 23, 2009 at 20:59.
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