Add different source term in diffusion equation at each time step

Lewis Liang · June 7, 2018, 07:44

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, 11:10

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, 07:44	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

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June 7, 2018, 11:10		#2
jpeter3 New Member JPeternel Join Date: Oct 2014 Posts: 19 Rep Power: 12	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.