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short question: zeroGradient equal fixedGradient=(0 0 0) ?!

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Old   July 16, 2013, 07:54
Default short question: zeroGradient equal fixedGradient=(0 0 0) ?!
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Andreas Ruopp
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Hello,

I looked at fixedGradientFvPatchField.C and
zeroGradientFvPatchField.C and for me

Code:
type fixedGradient;
value uniform (0 0 0);
behaves like using:
Code:
type zeroGradient;
So why do we have zeroGradient? fixedGradient type would be enough?!
Or do I draw the wrong conclusion?

Best regards,

Andy
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Old   July 16, 2013, 08:34
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Bernhard
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They are not the same. zeroGradient only garantuees the wall-normal derivative to be zero, not the complete gradient.
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Old   July 16, 2013, 12:52
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Andreas Ruopp
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Thank you for the fast answer. I got it.

Next little question:
A given fixedGradient value (a b c) will specify the gradient of for example U in the standard Coordinate-System(x,y,z) on a patch
HTML Code:
http://foam.sourceforge.net/docs/cpp/a00671.html#details
This boundary condition supplies a fixed gradient condition, such that the patch values are calculated using:


where
= patch values
= internal field values
= gradient (user-specified)
= inverse distance from patch face centre to cell centre

Hence, x_p is independent from the normal patch face vector?

Thanks for the answer in advance,

Andy
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boundary, condition, fixedgradient, zerogradient

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