[petsc-users] Solving a coupled multi-physics problem.

[Rahul Samala]

Hello PetSc users,

I request suggestions on how to do a coupled problem, in my case coupling between multiphase flow in porous media and deformation of porous media.I have successfully written and validated the flow code with 3 degrees of freedom (S-saturation, P-pressure, T-Temperature)
which uses SNES solver inside a time loop.  I have to use KSP solve for the deformation problem which has 1 degree of freedom (u-displacement).
For the coupled problem, the flow part now requires the displacement vector and the deformation part requires
the pressure field.

I have written a pseudo-code below. 
My idea is to use the second solution vector (displacement) in FormFunctionLocal belonging to SNES.
Since the DM used by SNES can be used for only one problem, a clone is made to be used for KSP.
Is this approach the correct way to solve this coupled problem.

typedef struct {    
    PetscScalar s; // Saturation
    PetscScalar p; // Pressure
    PetscScalar T; // Temperature
} Field;

typedef struct {    
    PetscScalar u; // Displacement
} Field2;

FormFunctionLocal(DMDALocalInfo *info, Field *sol, Field2 *sol2, Field *f, AppCtx *user)
{
........................
}

main()
{
    DM   da, newda; 
    Vec  sol;
    Vec  sol2;
    SNES  snes;
    KSP   ksp;

    SNESCreate(......, &snes);
    DMDACreate1d(........,&da);
    .
    .
    SNESSetDM(snes, da);
    DMClone(da, &newda);
    KSPCreate(.........,&ksp);
    KSPSetDM(ksp, newda);
    .
    .
    DMDASetUniformCoordinates(da,...........);
    DMDASNESSetFunctionLocal(da,...........,FormFunctionLocal);
    .
    DMCreateGlobalVector(da, &sol);
    DMCreateGlobalVector(newda, &sol2);    // This sol2 of type Field2 is passed to FormFunctionLocal.
    .
    do { // Time loop
    
    SNESSolve(snes,....);
    .
    .
    KSPSolve(ksp,......);    
    .
    .
    }while(criteria);  
}

Thank you,Rahul.




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