[swak4Foam] Boundary Conditions with GroovyBC, Normal Gradient

Peter Benovsky · December 14, 2012, 05:55

Quote:

Originally Posted by gschaider

You can only have one BC on a patch at a time. Have you made sure that groovyBC is actually evaluated on that patch (for instance by introducing a syntactic error into an expression - if it fails it's evaluated)

BTW: which version of OF?

2.1.1
What I meant is that I use groovyBC for the temperature. alphat uses standard alpatWallFunction, hence should not be groovyfied.

gschaider · December 14, 2012, 07:26

Quote:

Originally Posted by Peter Benovsky

2.1.1
What I meant is that I use groovyBC for the temperature. alphat uses standard alpatWallFunction, hence should not be groovyfied.

OK. Please provide some context (like which fields you used which BC on). It is not as absurd as you might think: I have seen people specifying 'type' twice hoping both would work.

Anyway: if the value 0 is only there during the first timestep then it is the same bug

Peter Benovsky · December 17, 2012, 10:44

Quote:

Originally Posted by gschaider

OK. Please provide some context (like which fields you used which BC on). It is not as absurd as you might think: I have seen people specifying 'type' twice hoping both would work.

Anyway: if the value 0 is only there during the first timestep then it is the same bug

It took longer than I thought but here it is (the context):

Code:

location "0";
object alphat;
 
heater
{
type alphatWallFunction;
value uniform 0.01;
}
 
object T;
 
heater
{
type groovyBC;
refValue uniform 300;
valueExpression "300"; 
gradientExpression "gradT*time()";
fractionExpression "0";
variables "heatFlux=100;gradT=heatFlux/(alphaEff);";
}

Without groovybc in the next time step I get for alphat:

Code:

location "0";
object alphat;
 
heater
{
type alphatWallFunction;
Prt                             0.85;
value nonuniform List<scalar>
.
.
.
}

With groovy bc it is just fixedValue with value=0
Cheers
Peter

gschaider · December 17, 2012, 13:30

Quote:

Originally Posted by Peter Benovsky

It took longer than I thought but here it is (the context):

Code:

location "0";
object alphat;
 
heater
{
type alphatWallFunction;
value uniform 0.01;
}
 
object T;
 
heater
{
type groovyBC;
refValue uniform 300;
valueExpression "300"; 
gradientExpression "gradT*time()";
fractionExpression "0";
variables "heatFlux=100;gradT=heatFlux/(alphaEff);";
}

Without groovybc in the next time step I get for alphat:

Code:

location "0";
object alphat;
 
heater
{
type alphatWallFunction;
Prt                             0.85;
value nonuniform List<scalar>
.
.
.
}

With groovy bc it is just fixedValue with value=0
Cheers
Peter

Hmm. That is strange. It should work. Could you try some things:

- instead of alphaEff add a constant (although I don't think that is the problem)
- set valueFraction to "uniform 0" (just to be sure)
- reset the 300 in the refValue to x. This should fail (this is just to make sure that it is really read)

Which version of swak do you use (check the start of the output of funkySetFields)

xuan8908 · February 21, 2014, 17:25

Hi, Bernhard,

I am trying to look at your codes of the groovyBC implementation. I am
curious where you pass those strings, like "valueExpression_" and
"gradientExpression_"? In the source code, groovyBCCommon.C, you just
look up those keywords from the dictionary file and read them. How do
those strings come into play to update the boundary condition? I guess
one of those source codes may contain the implementation of this. Could
you please tell me which source code is the right one that I can read
and learn from? Thanks a lot in advance. I will appreciate your reply.

gschaider · February 22, 2014, 12:23

Quote:

Originally Posted by xuan8908

Hi, Bernhard,

I am trying to look at your codes of the groovyBC implementation. I am
curious where you pass those strings, like "valueExpression_" and
"gradientExpression_"? In the source code, groovyBCCommon.C, you just
look up those keywords from the dictionary file and read them. How do
those strings come into play to update the boundary condition? I guess
one of those source codes may contain the implementation of this. Could
you please tell me which source code is the right one that I can read
and learn from? Thanks a lot in advance. I will appreciate your reply.

grep is your friend if you want to find the location of variables in the source code (of course there are more sophisticated tool, but this is installed on every system)

That'd be updateCoeffs in groovyBCFvPatchField.C. But the real magic happens in Libraries/swak4FoamParsers (especially everything with PatchValue in the beginning)

xuan8908 · February 22, 2014, 12:54

Thank you, Bernhard. I will take a look at it.

Sliwa · September 17, 2014, 05:40

Hello,

I am not sure this is the right thread for my question, but I was wondering if it was possible to set a fixed gradient in the direction normal to the patch and a fixed value in the tangential direction with groovyBC?

gschaider · September 17, 2014, 18:29

Quote:

Originally Posted by Sliwa

Hello,

I am not sure this is the right thread for my question, but I was wondering if it was possible to set a fixed gradient in the direction normal to the patch and a fixed value in the tangential direction with groovyBC?

There is a groovyBCDirection that wraps directionMixed (http://www.cfd-online.com/Forums/ope...-mixed-bc.html) but maybe this is not exactly what you need (no Dirichlet in tangential direction)

Sliwa · September 18, 2014, 11:56

Yes, I needed the Dirichlet in the tangential direction. Thanks anyway.

behzad-cfd · November 15, 2017, 15:57

Quote:

Originally Posted by gschaider

There is a groovyBCDirection that wraps directionMixed (http://www.cfd-online.com/Forums/ope...-mixed-bc.html) but maybe this is not exactly what you need (no Dirichlet in tangential direction)

Hi Bernhard,

I want to solve $\nabla^{2}\xi+\vec{n}\cdot\nabla\xi=0$ equation and obtain B that is defined like $\overrightarrow{B}=(\frac{\partial\xi}{\partial y})\vec{e_{x}}-(\frac{\partial\xi}{\partial x})\vec{e_{y}}$ .
I've implemented the equation in my base solver. Now i want to test functionality of the new solver but i have some boundary condition problem before testing.
For example if i want to get $\overrightarrow{B}=(0,1)$ in boundaries i need to set $(\frac{\partial\xi}{\partial y})=0$ and $-(\frac{\partial\xi}{\partial x})=1$ .

Can i use groovyBC for this?
How can i implement this BCs?

Thanks in advance,

gschaider · November 16, 2017, 21:16

Quote:

Originally Posted by behzad-cfd

Hi Bernhard,

I want to solve $\nabla^{2}\xi+\vec{n}\cdot\nabla\xi=0$ equation and obtain B that is defined like $\overrightarrow{B}=(\frac{\partial\xi}{\partial y})\vec{e_{x}}-(\frac{\partial\xi}{\partial x})\vec{e_{y}}$ .
I've implemented the equation in my base solver. Now i want to test functionality of the new solver but i have some boundary condition problem before testing.
For example if i want to get $\overrightarrow{B}=(0,1)$ in boundaries i need to set $(\frac{\partial\xi}{\partial y})=0$ and $-(\frac{\partial\xi}{\partial x})=1$ .

Can i use groovyBC for this?
How can i implement this BCs?

Thanks in advance,

I'm afraid not. Because if you have a boundary with constant x then $(\frac{\partial\xi}{\partial y})=0$ is not a boundary condition but a differential equation for the value on the boundary

behzad-cfd · November 17, 2017, 04:44

Quote:

Originally Posted by gschaider

I'm afraid not. Because if you have a boundary with constant x then $(\frac{\partial\xi}{\partial y})=0$ is not a boundary condition but a differential equation for the value on the boundary

Thanks for reply,
I should tell you that actually we have $\vec{A}=(0,0,\xi)$ and $\vec{B}=\nabla \times A = (\frac{\partial \xi}{\partial y}, -\frac{\partial \xi}{\partial x})$
So how can i set such a condition?!

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February 21, 2014, 17:25		#25
xuan8908 New Member Xuan Ge Join Date: Oct 2011 Location: Ames, IA, US Posts: 6 Rep Power: 15	Hi, Bernhard, I am trying to look at your codes of the groovyBC implementation. I am curious where you pass those strings, like "valueExpression_" and "gradientExpression_"? In the source code, groovyBCCommon.C, you just look up those keywords from the dictionary file and read them. How do those strings come into play to update the boundary condition? I guess one of those source codes may contain the implementation of this. Could you please tell me which source code is the right one that I can read and learn from? Thanks a lot in advance. I will appreciate your reply.

February 22, 2014, 12:54		#27
xuan8908 New Member Xuan Ge Join Date: Oct 2011 Location: Ames, IA, US Posts: 6 Rep Power: 15	Thank you, Bernhard. I will take a look at it.

September 17, 2014, 05:40		#28
Sliwa New Member Join Date: Jul 2013 Posts: 7 Rep Power: 13	Hello, I am not sure this is the right thread for my question, but I was wondering if it was possible to set a fixed gradient in the direction normal to the patch and a fixed value in the tangential direction with groovyBC?

September 18, 2014, 11:56		#30
Sliwa New Member Join Date: Jul 2013 Posts: 7 Rep Power: 13	Yes, I needed the Dirichlet in the tangential direction. Thanks anyway.