Hi Fabian,

What you describe is what I believe is going on. I am however cc’ing Hui since he uses this regularly. Perhaps once this is clarified we can determine what else to add to the user guide to make it clearer.

Cheers,
Spencer.
On 20 Oct 2016, at 15:11, Selbach, Fabian <fabian.selbach@student.uni-siegen.de> wrote:

Dear Community,

I would like to know more about how to implement damping-zones in detail.

Of course I already found the example with the following structure, but no other information about the mathematical background of this "Absorption-Forcing" and the definitions of RefFields and SpongeCoeffizient :

        <!-- Define reference fields /-->
        <FUNCTION NAME="RefFields">
            <E VAR="u" VALUE="-y*y+1" />
            <E VAR="v" VALUE="0" />
            <E VAR="p" VALUE="0" />
        </FUNCTION>
        <FUNCTION NAME="SpongeCoefficient">
            <E VAR="u" VALUE="-100*(x>2.5)" />
            <E VAR="v" VALUE="-100*(x>2.5)" />
        </FUNCTION>
    </CONDITIONS>
    <FORCING>
        <FORCE TYPE="Absorption">
            <COEFF> SpongeCoefficient </COEFF>
            <REFFLOW> RefFields </REFFLOW>
        </FORCE>
    </FORCING>
With the SpongeCoefficient function I define the space where my sponge zone starts, am I right? So in this example it starts from x>2.5, but what about the -100? Is it some kind of function like u _damp = -100*u*(-y*y+1)? I'm not sure about that and there are no information in the user-guide. Can somebody explain that in more detail? And do I have to care any other modifications?

Thanks for any answer!

Best regards
Fabian
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Spencer  Sherwin
McLaren Racing/Royal Academy of Engineering Research Chair, 
Professor of Computational Fluid Mechanics,
Department of Aeronautics,
Imperial College London
South Kensington Campus
London SW7 2AZ

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