[petsc-users] Fluid-Structure interaction with multiple DMPlex

[Matthew Knepley]

On Tue, Jan 11, 2022 at 2:59 PM Thibault Bridel-Bertomeu <
thibault.bridelbertomeu at gmail.com> wrote:

> Le mar. 11 janv. 2022 à 16:36, Jed Brown <jed at jedbrown.org> a écrit :
>
>> Thibault Bridel-Bertomeu <thibault.bridelbertomeu at gmail.com> writes:
>>
>> > Hello everybody,
>> >
>> > So, let's say i have the mesh attached to this email that has 2 physical
>> > surfaces and 5 physical curves. This gives me 2 strata in the "Cell
>> Sets"
>> > and 5 strata in the "Face Sets".
>> > Would something like the following piece of code be the right way to
>> > "extract" and manipulate each stratum of the "Cell Sets" to assign them
>> a
>> > DS, a TS etc...?
>> >
>> >     DMLabel surfacesLabel;    ierr = DMGetLabel(dm, "Cell Sets",
>> > &surfacesLabel);CHKERRQ(ierr);    IS fluidIS;    ierr =
>> > DMLabelGetStratumIS(surfacesLabel, 2, &fluidIS);CHKERRQ(ierr);
>> > DMLabel fluidLabel;    ierr = DMLabelCreate(PETSC_COMM_WORLD, "Fluid",
>> > &fluidLabel);CHKERRQ(ierr);    ierr = DMLabelSetStratumIS(fluidLabel,
>> > 1, fluidIS);CHKERRQ(ierr);
>> >
>> > Once I have the Fluid label linked to the fluidIS (same for the
>> > solid), should I call DMPlexLabelComplete on both the labels before
>> > proceeding and calling the DMCreateSubDM with their IS ?
>>
>> How do you want to implement the function space and interface condition?
>> As single-valued temperature seen from both sides? With a discontinuous
>> space and a surface integral? Euler equations are commonly solved in
>> conservative variables, thus you don't have an option of a continuous
>> temperature space.
>>
>
> A priori, the job of the fluid is to provide a certain heat flux to the
> solid that will subsequently warm up. So I am not expecting that both fluid
> and solid will have the same temperature at the interface, it will indeed
> be discontinuous.
> I do not get why you mention a surface integral though ?
> Anyways, for now, I do not really know how to handle this boundary
> condition problem ... it is one of the _big_ items of my todo list and I
> think I'll need your help.
>

Hmm, let's start here because that does not make sense to me. Can you write
down the mathematical model? Usually I think of temperature as being
a continuous field. I have only seen discontinuities for rareified gases.

  Thanks,

    Matt


> For now, I am trying to figure out how to handle both discretizations, and
> I am going the following way :
>
> // Set up the discrete systems for both domains
> //+ Fluid is finite volumes
> PetscFV fluidFV;
> ierr = PetscFVCreate(PetscObjectComm((PetscObject) dm), &fluidFV);CHKERRQ
> (ierr);
> user->dof = 4;
> ierr = PetscFVSetNumComponents(fluidFV, user->dof);CHKERRQ(ierr);
> PetscInt dim;
> ierr = DMGetDimension(dm, &dim);CHKERRQ(ierr);
> ierr = PetscFVSetSpatialDimension(fluidFV, dim);CHKERRQ(ierr);
> ierr = PetscObjectSetName((PetscObject) fluidFV, "EulerEquation");CHKERRQ
> (ierr);
> ierr = PetscFVSetType(fluidFV, PETSCFVLEASTSQUARES);CHKERRQ(ierr);
> ierr = PetscFVSetComputeGradients(fluidFV, PETSC_FALSE);CHKERRQ(ierr);
> PetscInt fluidFieldNum = 0;
> ierr = DMSetField(dm, fluidFieldNum, fluidLabel, (PetscObject) fluidFV);
> CHKERRQ(ierr);
> ierr = DMViewFromOptions(dm, NULL, "-dm_fv_view");CHKERRQ(ierr);
> //+ Solid is finite elements
> PetscBool simplex;
> ierr = DMPlexIsSimplex(dm, &simplex);CHKERRQ(ierr);
> PetscFE solidFE;
> ierr = PetscFECreateDefault(PetscObjectComm((PetscObject) dm), dim, 1,
> simplex, "heateqn_", -1, &solidFE);CHKERRQ(ierr);
> ierr = PetscObjectSetName((PetscObject) solidFE, "HeatEquation");CHKERRQ
> (ierr);
> PetscInt solidFieldNum = 1;
> ierr = DMSetField(dm, solidFieldNum, solidLabel, (PetscObject) solidFE);
> CHKERRQ(ierr);
> ierr = PetscFEDestroy(&solidFE);CHKERRQ(ierr);
> ierr = DMViewFromOptions(dm, NULL, "-dm_fe_view");CHKERRQ(ierr);
> // //+ Sub-DM for the fluid domain
> // DM fluidDM;
> // IS subFluidIS;
> // ierr = DMCreateSubDM(dm, 1, &fluidFieldNum, &subFluidIS,
> &fluidDM);CHKERRQ(ierr);
> // ierr = DMViewFromOptions(fluidDM, NULL, "-fluid_dm_view");CHKERRQ(ierr);
> // //+ Sub-DM for the solid domain
> // DM solidDM;
> // IS subSolidIS;
> // ierr = DMCreateSubDM(dm, 1, &solidFieldNum, &subSolidIS,
> &solidDM);CHKERRQ(ierr);
> // ierr = DMViewFromOptions(solidDM, NULL, "-solid_dm_view");CHKERRQ(ierr);
> //+ Create the DS covering both domains
> ierr = DMCreateDS(dm);CHKERRQ(ierr);
> ierr = DMViewFromOptions(dm, NULL, "-dm_ds_view");CHKERRQ(ierr);
> //+ Sub-DS for the fluid domain
> PetscDS fluidDS;
> ierr = DMGetRegionNumDS(dm, fluidFieldNum, &fluidLabel, &fluidIS,
> &fluidDS);CHKERRQ(ierr);
> ierr = PetscDSViewFromOptions(fluidDS, NULL, "-fluid_ds_view");CHKERRQ
> (ierr);
> //+ Sub-DS for the solid domain
> PetscDS solidDS;
> ierr = DMGetRegionNumDS(dm, solidFieldNum, &solidLabel, &solidIS,
> &solidDS);CHKERRQ(ierr);
> ierr = PetscDSViewFromOptions(solidDS, NULL, "-solid_ds_view");CHKERRQ
> (ierr);
>
> I am not sure where I am going with this for now, I am really
> experimenting ...
> I tried generating two sub-DMs because it seemed to me that, that way, I
> could have two TS and basically work my two problems independently and
> figure out the interface later. But! When I printed them (with
> fluid_dm_view and solid_dm_view), it seemed that something was wrong : the
> fluidDM showed a FEM field and both sub DMs appeared to know the whole mesh
> and all the strata of all the fields.
> The next step is to figure out the FEM for the heat equation -- I have the
> details for the FVM in another code, it should be pretty straightforward.
> The following step will be to plug in a timestepper, or two timesteppers.
> Then the interface and the connection between the two problems.
>
> Thanks for your help and all your input, as always !!!!
>
> Cheers,
> Thibault
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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