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swak4Foam to calculate bubble velocity

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Old   March 1, 2012, 13:28
Default swak4Foam to calculate bubble velocity
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Nima Samkhaniani
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hi former
i guess, it should be possible to access a bubble velocity with swak4Foam
but i dont know how the procedure can be?
the procedure should be like that:

1) select all cells with alpha < 0.5
2) calculate the gravity center in each time step

any comment or suggestion?
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Old   March 1, 2012, 15:10
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Bernhard Gschaider
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Quote:
Originally Posted by nimasam View Post
hi former
i guess, it should be possible to access a bubble velocity with swak4Foam
but i dont know how the procedure can be?
the procedure should be like that:

1) select all cells with alpha < 0.5
2) calculate the gravity center in each time step

any comment or suggestion?
Why use a cutoff? that way you're going to get jumps in your result. Something like

"(pos()*vol()*(1-alpha1))/sum(vol()*(1-alpha1))"

(with an accumulation sum) might give you the center of the "non-fluid".Have a look at my presentation from the last workshop (you'll find it on the swak4Foam-page on the Wiki). Slide 76 has a similar application.

BTW: if you're interested in the velocity of the liquid interface then you might want to have a look at slide 155 where it s demonstrated how to calculate that with sampledSurfaces
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Old   May 24, 2016, 14:56
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Arsalan
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Hi Foamers,

I'm doing a 3D simulation of two and three bubble rising using a modified interFoam solver and I need to bubbles centre position, velocity and surface area.

For a single bubble rising I used swak4Foam expressions for example for bubble centre position in Y as follows :
Code:
    bubbleCentreY
    {
        type swakExpression;
        valueType internalField;
        verbose true;
    variables (
    "Vol= sum (alpha1 < 0.5 ? vol() : 0);"
    "VolY= sum (alpha1 < 0.5 ? pos().y*vol() : 0);"    
    );        
    expression "VolY/Vol";
        accumulations (
        min        
        );

     
    }
Is there a way to compute two or three bubble properties in this manner?

Thanks in advance,
Best Regards,
Arsalan.
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