[meth]

I want to impose a dirichlet boundary condition in Openfoam on the inlet patch with a time varying value calculated in each time step. For a example U = ( 1 y 0), where y is a value that I am calculating in each time step inside the solver. I know I have to use fixedValue type boundary condition which is uniform. Is there any inbuilt boundary condition which I can directly use or, do I need to create my own one? If I have to create a new boundary condition can you please give me some ideas and references.

Thank you 

Methma

[fabian_roesler]

class Foam::uniformFixedValueFvPatchField< Type >

This boundary condition provides a uniform fixed value condition.

Example of the boundary condition specification:

myPatch
{
    type uniformFixedValue;
    uniformValue constant 0.2;
}

Note: The uniformValue entry is a DataEntry type, able to describe time varying functions. The example above gives the usage for supplying a constant value.

Search the Doxygen next time.

Cheers

Fabian

[meth]

Hi Fabian,

Thank you for your reply

I am little confused about uniformFixedValue boundary condition. Can you please give more details about it.

My questions are;

What is the difference between fixedValue Boundary condition and uniformFixedValue boundary condition?
Can I impose this boundary condition for the vector field, U?
If so, how should I describe the uniformValue?
I want to set U=[1 y 0], where y changes in each time step, and the values of y can be find from a dictionary. Do you know how to do this?

Thank you again

Best,
Methma

[fabian_roesler]

Hi Methma

On the OpenFOAM page and in this forum you can find the following links:
http://www.openfoam.org/version2.1.0...conditions.php
http://www.cfd-online.com/Forums/ope...condition.html
http://www.cfd-online.com/Forums/ope...how-field.html

They will give enough information and eventually will point you to a tutorial for this BC.

Here is the velocity BC for your problem:

type uniformFixedValue;
uniformValue table       
(       
    ( 0 (1 0 0))
    (10 (1 1 0))
    (20 (1 2 0))
    (xy (1 z 0))
);

first column is the time, second column is the velocity vector in brackets.

Cheers

Fabian

[meth]

Thank you very much Fabian I did it.

[meth]

Hi Fabian,

We can you uniformFixedValue boundary condition to obtain a time dependent dirichlet boundary condition on a patch. I am setting uniformValue to tableFile in my simulations. If I update the tablefile with time dose it automatically update the boundary values in each time step? or It always proceed with the data in the tablefile stored at the beginning?

I think it does not read the table file in each time step.

Best,

Methma

[fabian_roesler]

Sorry for the late response. I guess you are right. The table is not run-time-modifiable.

Cheers

Fabian

[fengyi]

Hi Methma
I meet this problem, too. I'd like to change the boundary condtion accoring to some value calculated from last time step, and I have no idea about how to make the boundary condition be run-time-adjustable.

Have you solved this problem? Could you please show me the idea? Or, can some seniors having a solution to this problem give me some advices?

Thank you.


Best regards,

Feng

[leorasy89]

Thank you for sharing, they are very helpful for me

[piu58]

@Feng

A very easy way would be a batch job
- calculating to some destination time
- calculated the new b.c. outside OF and write it in the "last time" folder
- calculate the next time period.

You may set the calculated times as short as your accuracy needs.

[fengyi]

Originally Posted by piu58

@Feng

A very easy way would be a batch job
- calculating to some destination time
- calculated the new b.c. outside OF and write it in the "last time" folder
- calculate the next time period.

You may set the calculated times as short as your accuracy needs.

Dear Pilz
Thanks for your reply.
It is a practical solution for this problem. I am thinking about performing this process automatically:
(1)---use functions in CONTROlDICT to calculate the boundary condition(such as magnitude of incoming velocity) at the end of every time step, and output it as a txt in the home directory.
(2)---the boundary condition read the information provided by txt at the beginning of the next time step to be run-time-adjustable.
(3)---run next time step according to the new boundary condition.
(4)---finish the next time step and repeat(1)

I have no idea about process(3). As I am a fresh man about Foam, I don't know how to code the boundary condition to make the it read the infomation provided by the txt in the home directory constantly.
I try to use the (#include 'the txt') in the boundary contion to read the infomation(maybe stupid or even wrong, forgive me), but I fail. Because the syntax (#include 'the txt') will be replaced with the information provided in the txt, so the (#include 'the txt') only work once at the first time step. Is there exist some function or syntax which can be used on this contion to read the information in the txt continuously during all the run time?


Best regards,

Feng

[victorable]

Originally Posted by fengyi

Hi Methma
I meet this problem, too. I'd like to change the boundary condtion accoring to some value calculated from last time step, and I have no idea about how to make the boundary condition be run-time-adjustable Drift Boss.

Have you solved this problem? Could you please show me the idea? Or, can some seniors having a solution to this problem give me some advices?

Thank you.


Best regards,

Feng

Kind of like me when I'm trying to wait for a solution, but I'm in vain.