Dear All,
I have a class which represents a velocity field (I am using a variant of
the pressure correction navier stokes model with two phases) and a class
which represents a transport model along a provided velocity field. I am
adding in some terms into the velocity model (currently surface tension but
soon to be added is the canham-helfrich or willmore energy) accounting for
the physics and force balance on the boundary between the two phases. The
approach that we are using is to create a block structure inside the
velocity class to incorporate these other physics into the model. We have
a splitting of velocity separate from the pressure terms and have separate
dofhandlers for these two groups but now we are lumping all the components
that need to be simultaneously solved for with the velocity into the
velocity dofhandler and fesystem. For instance we have the block
components in the velocity fesystem:
dim components of velocity, normal velocity, curvature and willmore energy
so that our velocity fesystem looks like
FESystem<dim> (
FESystem<dim>(FE_Q<dim>
(parameters.degree_of_fe_velocity),dim), 1, // velocity
FE_Q<dim>(parameters.degree_of_fe_velocity),
1, // normal velocity
FE_Q<dim>(parameters.degree_of_fe_velocity),
1, // curvature
FE_Q<dim>(parameters.degree_of_fe_velocity), 1
// willmore force
)
I have figured out how to construct the block sparsity patterns and
matrices etc and solve for this, but at the end of the day this class
represents a velocity not a velocity plus other stuff. This class
interfaces with the other class representing transport and I need to be
able to provide a velocity, dofhandler and fesystem in such a way that I
don't break encapsulation ie the other class doesn't need to know that
internally there was a block system and other components...
The other class expects to be able to query a
TrilinosWrappers::MPI::Vector, FESystem<dim> and DoFHandler<dim>
representing the velocity finite element solution.
Supposing internally to the velocity class I have
solution, a TrilinosWrapper::MPI::BlockVector
fe_system, the FESystem<dim> described above and
dof_handler, the associated DoFHandler<dim> which is sorted
DoFRenumbering::hierarchical and DoFRenumbering::component_wise.
Supposing velocity_block represents the block number associated to the
velocity components, I noticed that solution.block{velocity_block} would be
a TrilinosWrapper::MPI::Vector of the velocity as desired and it is
possible to extract the sub FiniteElement
fe_system.base_element{velocity_block} corresponding only to the velocity,
but the dof_handler has no such existing capability and if I pass it as is
with the extracted FiniteElement into an FEValues, an assertion is
triggered when we call fe_values.reinit(cell) saying that the given finite
element does not match the dofhandler's finite element... I don't want to
pass the entire system since that requires the other class to know that it
only needs the first block components etc.
My question is this: What would be a best approach to dealing with this?
Is there currently a way to extract a "diagonal block" from the system and
reduce the solution, fesystem and dofhandler to only represent that part?
Do I need to create a new FESystem, DoFHandler and vector to provide the
functionality I need ?
I hope this is clear enough and enough(and not too much) background to
understand what I am asking. Thanks for any help!
Spencer Patty
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