Hi Fabian, *where my sponge zone starts, am I right? * You need to define the start by using a boolean-expression combination of inequalities which is adopted to identify your sponge region. *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)**?* For DNS, you need a reference field and generally, we use base flows (sometimes, mean flows). Then, you can define a friction term (forcing term) as follows: -sigma(X)(u-u_ref) Certainly, the absorbing strength can be a function (polynomial or Rayleigh like expressions) which you can find in some literature. e.g. for 1D, 3125(L-x)(x-x_s)^4/(256(L-x_s)^5) For linear NSEs, it is simpler -sigma(X)u *And do I have to care any other modifications?* No. The simplest way is to modify the definition of sigma(X). Hope it will be helpful. Cheers, Hui On 20/10/16 15:11, Selbach, Fabian 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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