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Old   May 9, 2023, 10:37
Default uniformFixedValue Boundary condition
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Hi all
I am using OpenFOAMv10, and currently working on a case such that I need to have the velocity field for a patch called droplet (Boundary condition in 0th folder) used within another dimensionless field called alpha as a condition for the same patch droplet.

For that I am using uniformFixedValue type coded.
(I am trying to use it as a groovyBC)

As I am not that good with coding it results in error that U is an unknown identity.

I am attaching the code for that patch droplet of alpha field as below:

type uniformFixedValue;
uniformValue coded;
name drop;
#include "mathematicalConstants.H"

const volScalarField& U = this->db().lookupObject<volScalarField>("U");
return scalar(mag(U) > 1e-9) ? 1.0 : 0.0); // U as velocity from the boundary condition file 'U'


Thanking in advance.
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Old   May 9, 2023, 13:49
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Mark Olesen
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If you have the option to use OpenFOAM-1912 or later, you have expressions (many ideas similar to swak4foam) - you can simply specify the uniformValue type as "expression" and go from there without any additional compilation.

If you do decide to stick with coded, remember that you are trying to write a boundary condition. This means that you need to access the corresponding boundary values of your velocity field (not the entire volume field). The velocity field is of course also a volVectorField not a volScalarFIeld either.

After you get at the boundary field part of "U", remember that you need to return a field of values, not just a single scalar.
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Old   May 10, 2023, 16:38
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Hi olesen

Thanks for your quick reply and correcting out my mistake with the vector part. Though even if I do that I am still unable to access the velocity from Velocity boundary file for the droplet patch. It states an error that 'U' was not declared in the scope.
How do I get access/read to the velocity field for the patch droplet in the alpha boundary file?

Thanks in advance.

(Unfortunately I am bound to use only OpenFOAMv10 for this!)
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groovybc, openfoam 10, uniformfixedvalue

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