CFD Online Discussion Forums - [swak4Foam] GroovyBC

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Hi

I'm trying to use groovybc to specify an inflow condition, however i'm kinda stuck with it. my c++ knowledge is very limited.

the velocity profile i'm trying to implement is

U=min(y,kln(y)+B) , 0 , 0

where k and B are constants, y is the y coordinate of the point. Velocity is only streamwise, the other 2 components at the inlet are 0.

I can create yp=y and kln=k*log(yp)+B, however I don't how to choose the minimum of these two.

I'm using OF 1.7

thanks for any help

Quote:

Originally Posted by longamon (Post 300763)

The min-function in groovyBC takes the minimum of a field and therefore only takes one argument.

The minimum of two fields a and b can be taken with the ?:-notation: (a < b ? a : b)

:D
thanks gschaider, that worked like a charm. kudos on the groovyBC app, great tool.

Hi, its me again. Upgraded to OF 2.0 and installed swak4foam, however the notations has changed a bit. This is the entry for the boundary "Entrada"

Code:

   Entrada

      {

        type            groovyBC;

        valueExpression "vector(ret*nu*v/1.5,0,0);";

        variables       "ret{Entrada}=590;nu{Entrada}=0.000138217;y1{Entrada}=pos().y;ymax{Entrada}=max(y1);y2{Entrada}=ymax-pos().y;yi{Entrada}=(y1<y2?y1:y2);yp{Entrada}=ret*yi/1.5;klny=2.5*log(yp+0.000001)+5;v{Entrada}=(yp<klny?yp:klny);";

        value           uniform (1 0 0);

      }

and it throws this error:

Code:

--> FOAM FATAL ERROR: 

 Parser Error at "1.5-6" :"field y1 not existing or of wrong type"

"max(y1)"

"     ^^"

Appreciate your help

David

Quote:

Originally Posted by longamon (Post 319606)

Hi, its me again. Upgraded to OF 2.0 and installed swak4foam, however the notations has changed a bit. This is the entry for the boundary "Entrada"

Code:

   Entrada

      {

        type            groovyBC;

        valueExpression "vector(ret*nu*v/1.5,0,0);";

        variables       "ret{Entrada}=590;nu{Entrada}=0.000138217;y1{Entrada}=pos().y;ymax{Entrada}=max(y1);y2{Entrada}=ymax-pos().y;yi{Entrada}=(y1<y2?y1:y2);yp{Entrada}=ret*yi/1.5;klny=2.5*log(yp+0.000001)+5;v{Entrada}=(yp<klny?yp:klny);";

        value           uniform (1 0 0);

      }

and it throws this error:

Code:

--> FOAM FATAL ERROR: 

 Parser Error at "1.5-6" :"field y1 not existing or of wrong type"

"max(y1)"

"     ^^"

Appreciate your help

David

Hmm. At first: You're working on the patch Entrada anyway, so there's no need to write the variables like this "ret{Entrada}=590" ("ret=590" is sufficient).

In my opinion this should not be the cause of your problem, but could you try it anyway? BTW: Using the external-variables syntax might lead to strange results if used on the "same" patch as external variables always get only one value (which is used for all faces).

That was it, y1{Entrada}=pos().y was supposed to be a vector and it wasn't

thanks

Hail all,
My c++ skill is quite low. Much like the original post I wish to compare to vector fields and get the minimum.
Basically I want:
U=(min(1,pos()z),0,0)

I was wondering how I would go about generating a field of uniform values 1. At the moment my work around is to use field2=(pos().z/pos().z). And seeing as this produces the result I want I'm not exactly complaining as much as I wish to know the 'correct' way to do it in the future.

And so i use:
variables "d=pos().z/pos().z;e=pos().z;profile=(e < d ? e : d)*vector(1,0,0);";
valueExpression "profile";

Its probably something really obvious or implied that I'm not aware of,
Striving for elegance, and Cheers

Quote:

Originally Posted by RygeltheXVI (Post 333192)

Since the release that has the date 2011-07-26 (check the README) there is a binary min/max in the parser. So basically

vector(min(pos().z,1),0,0)

should work