groovyBC boundary using values from another boundary
 

Dear all
I have been studying the groovyBC boundary condition these days.But I am confused in understanding something.
The following is my inputing file for pressure p.
-------------------------------------------------------------------------------------------------------

dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{

SIDE
{
type groovyBC;
value uniform 0.1;
valueExpression "Pside";
variables "Pside@SIDE=p;";
}
OUT
{
type zeroGradient;
}
IN
{
type zeroGradient;
}
}
----------------------------------------------------------------------------------------------------------
Does it mean that I am using the state of the fields P on the same patches(in my case it is SIDE) from the previous time-step or iteration to evaluating the pressure expression in run-time?

According the original description from website http://openfoamwiki.net/index.php/Contrib_groovyBC
"groovyBC provides the ability to access fields from remote patches (other patches present within the current simulation). When evaluating the expression in run-time, the state of the fields on the remote patches from the previous time-step or iteration are utilised."

Have I understood it correctly?
Thank you for your suggestion!


lg88

It's a bit more complicated than that: if the solver does multiple iterations per timestep then for later iterations p will be the updated value. Your expression basically sets p uniformly to the average of what p currently is (which is technically the value of the last time).

Newer versions of groovyBC have the possiblity to access the p from the last time with "oldTime(p)".

Form the @ in your remote patch-access I deduce that you're using a non-swak4Foam version of groovyBC (the syntax there is different). "oldTime" won't work there anyway

Hi gschaider
I have installed swak4Foam in my computer for the purpose of using function 'oldTime'.I need the calculated value of the last time not the average value.So I have changed my inputing P file as follow:
----------------------------------------------------------------------------------------------------
dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{

SIDE
{
type groovyBC;
value uniform 0.1;
valueExpression "Pside";
variables "Pside{SIDE}=oldTime(p);";
}
OUT
{
type zeroGradient;
}
IN
{
type zeroGradient;
}
}

-----------------------------------------------------------------------------------------------------------------
But when I run my case,it came out some warnings as:
I guessed the solver had token the average value as the boundary condition from the warning.Do you know what is wrong with it?

Regards!

lg88

Just write
the values are always averaged if you us the "remote" notation for variables. Even if "remote" is the same patch

shredder BC instead of coupling
 

Dear Jack, dear Bernhard,

I have the same warning when running scalarTransportFoam on my case.
My case is a simple simulation of a rectangular channel after a delta-shaped SuperFocus mixer. Since the nozzles of fluid A and B alternate, my initial condition is a nice alternating pattern A-B-A-B-A
https://dl.dropboxusercontent.com/u/..._condition.png
The fluid moves steadily in negative z direction.
The upper inlet patch is coupled to the lower one via groovyBC
Even changing it to "oldTime(T)" still yields the solver warnings.
The results are like a shredder boundary condition:
Instead of a coupling, that reproduces the values at the outlet, I get this:
https://dl.dropboxusercontent.com/u/...ot_working.png

Neither my supervisor nor me can think of any simpler yet adequate other BCs.
Any advice?

I have discussed this multiple times here: "remote" variables can only be uniform. But what would be appropriate for your example would be a "mapped"-boundary. See the pitzDailyMapped in the tutorials and n swak in Examples/tests/ the mapping examples (although they do more than what you might need)

The sign "-" in groovyBC
 

I have confused, When I use groovyBC to set the input of the velocity, such as this
The problem here is the sign "-" before para. Its physical meaning ?

When I do not use it, the velocity will be in the opposite direction, ie the velocity input from outlet .

Thanks,

best regards,


takasi

Dear Takasi,
short answer: try long answer: openFoam regards the minus sign as a binary operator (e.g. "a - b") so that it cannot stand on its own. The unary minus sign (e.g. "-c") can thereby be used by multiplying a term with -1.

I hope, this solves your problem!
Greetings,
Yeru

Strange. groovyBC should know how to handle a unary minus

did u solve ur problem?
I am having the same warning, in 1D the result is ok, but in 2D i can not have convergence