Add different source term in diffusion equation at each time step

Lewis Liang · June 7, 2018, 06:44

Dear Foamers,

I'm recently working on adding a series of source term into my governing equation in sovler B, which is a normal form of diffusion equation. More specifically, the source term calculated by another OF solver A. And the computational domain in both solver A and B are kept the same. It means that, at one time step, the solver B solve the diffusion equation by adding the corresponding time step result solved by solver A as a source term. In other words, the source term will re-load into the solver at each time step. So far, I'm sill looking for a way to do so. And I search on the CFD forum, some of people advised applying the fvOptions function or "udf.h" as introduced as below:

reading in a field into fvOptions with type: scalarCodedSource

Read txt file and import values to source term.

But it still confuses me a lot. Could anyone help out of this problem?

Thanks in advance!

Regards,

Lewis

jpeter3 · June 7, 2018, 10:10

I do not know for any build in solutions for such a thing ... The udf.h example is not for OpenFOAM, this way custom functions are passed to solver in Ansys FLUENT program. And the other code snippet you pinned is a modification done to C++ source code of one of OpenFOAM solvers. It is a nice solution, if your source is time-independent.

Note that in openFoam, modifications are usually possible by modifying the source code of selected solver and compiling it under a different name, so basically rewriting the program.

Assuming, you would want to program the thing in C++ and compile your own solver, here are some suggestions:

You can load fields in same way as they are initialized in createFields.H, just put the code for e.g. myScalarField initializiation inside the main loop. When you run the solver B over the case result files of solver A, this will read myScalarField in each of solver A result files. But, this is like a post-process activity, that executes only at times solver A had written.

However, this may become tricky if you want to run solver B as normal solver (with some timesteps in between write times). Your solver A results (along with myScalarField) are not written at every time step ... some how, you would need to catch same write times in solver B as in solver A, write results of B, load myScalarField from time directory written by solver A and then assume that it doesnt change till the next write time of solver A ... Sounds complicated.

My suggestion, build a solver that incorporates solver A and solver B sequentially. This way you can share data easilly and calculate the whole thing in one throw.

June 7, 2018, 06:44	Add different source term in diffusion equation at each time step	#1
Lewis Liang Member Lewis Join Date: Jun 2016 Posts: 34 Rep Power: 10	Dear Foamers, I'm recently working on adding a series of source term into my governing equation in sovler B, which is a normal form of diffusion equation. More specifically, the source term calculated by another OF solver A. And the computational domain in both solver A and B are kept the same. It means that, at one time step, the solver B solve the diffusion equation by adding the corresponding time step result solved by solver A as a source term. In other words, the source term will re-load into the solver at each time step. So far, I'm sill looking for a way to do so. And I search on the CFD forum, some of people advised applying the fvOptions function or "udf.h" as introduced as below: reading in a field into fvOptions with type: scalarCodedSource Read txt file and import values to source term. But it still confuses me a lot. Could anyone help out of this problem? Thanks in advance! Regards, Lewis

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
courant number increases to rather large values	6863523	OpenFOAM Running, Solving & CFD	22	July 5, 2023 23:48
what is swap4foam ??	AB08	OpenFOAM	28	February 2, 2016 01:22
How to write k and epsilon before the abnormal end	xiuying	OpenFOAM Running, Solving & CFD	8	August 27, 2013 15:33
dynamic Mesh is faster than MRF????	sharonyue	OpenFOAM Running, Solving & CFD	14	August 26, 2013 07:47
plot over time	fferroni	OpenFOAM Post-Processing	7	June 8, 2012 07:56

June 7, 2018, 10:10		#2
jpeter3 New Member JPeternel Join Date: Oct 2014 Posts: 19 Rep Power: 11	I do not know for any build in solutions for such a thing ... The udf.h example is not for OpenFOAM, this way custom functions are passed to solver in Ansys FLUENT program. And the other code snippet you pinned is a modification done to C++ source code of one of OpenFOAM solvers. It is a nice solution, if your source is time-independent. Note that in openFoam, modifications are usually possible by modifying the source code of selected solver and compiling it under a different name, so basically rewriting the program. Assuming, you would want to program the thing in C++ and compile your own solver, here are some suggestions: You can load fields in same way as they are initialized in createFields.H, just put the code for e.g. myScalarField initializiation inside the main loop. When you run the solver B over the case result files of solver A, this will read myScalarField in each of solver A result files. But, this is like a post-process activity, that executes only at times solver A had written. However, this may become tricky if you want to run solver B as normal solver (with some timesteps in between write times). Your solver A results (along with myScalarField) are not written at every time step ... some how, you would need to catch same write times in solver B as in solver A, write results of B, load myScalarField from time directory written by solver A and then assume that it doesnt change till the next write time of solver A ... Sounds complicated. My suggestion, build a solver that incorporates solver A and solver B sequentially. This way you can share data easilly and calculate the whole thing in one throw.