Thanks Daniel.
I will try the first approach. My time dependent Function class returns an
update and not a new value. Actually, I am trying to solve a free surface
flow problem with moving mesh(for very small displacements). I am
implementing the flow and mesh movement in a decoupled way. So at the end
of every time step I get the flow solution(velocity and pressure). So I
advect(displace) the free surface vertices as (U_{t_n} +
U_{t_{n+1}})*time_step/2. This is the incremental displacement which I want
to add to previous displacements. I use this free surface boundary
displacements to solve for the interior vertices displacements using a
simple 'laplacian'(which is linear and thus laplacian_system_matrix is
assembled only once). And finally apply these displacements to the entire
(initial)mesh.
Of course all this can be done using just incremental displacements instead
of cumulative displacement(as I am moving the mesh anyway at every time
step), I just want to try with cumulative.
I will revert for any further clarifications.
Thanks,
Bhanu.
On Monday, December 4, 2017 at 4:54:11 PM UTC+5:30, Daniel Arndt wrote:
>
> Bhanu,
>
> [...]
>> VectorTools::interpolate_boundary_values(move_dof_handler, 106,
>> move_boundary_values_function, move_boundary_values);
>> MatrixTools::apply_boundary_values(move_boundary_values,
>> move_system_matrix, move_solution, move_system_rhs);
>>
>> instead of 'constraints'.
>> Now, I have to add the current time step dirichlet values to the
>> 'previous cumulative dirichlet values at this boundary' in my
>> 'move_boundary_values_function' object of type 'template <int dim> class
>> MoveBoundaryValues106 : public Function<dim>'. How can I accomplish this in
>> my member function
>>
>> template <int dim>
>> void MoveBoundaryValues106<dim>::vector_value(const Point<dim> &p,
>> Vector<double> &values) const
>> {
>> // std::vector<Tensor<1,dim>>
>> previouscumulative(n_boundary_dofs_of_type_106);
>> const double time = this->get_time();
>> previuouscumulative += get_function_values();
>>
>> values[0] = previouscumulative[];
>> values[1] = previouscumulative[];
>> values[2] = previouscumulative[];
>> values[3] = previouscumulative[];
>> }
>>
> So you have a time-dependent Function class that only returns an update
> instead of the new value?
> In this case, I would still call
>
> VectorTools::interpolate_boundary_values(move_dof_handler, 106,
> move_boundary_values_function, move_boundary_values_update);
>
> and add to the previous vector
>
> for (auto& it=move_boundary_values.begin();
> it!=move_boundary_values.end(); ++it)
> it->second += move_boundary_values_update[it->first];
>
> Since move_boundary_values are also just the boundary values for your
> previous solution, you could also compute move_boundary_values on the fly
> by extracting the boundary DoFs using DoFTools::extract_boundary_dofs
> <https://www.dealii.org/8.5.1/doxygen/deal.II/namespaceDoFTools.html#ad3067f335a97de429176178689222f3a>
>
> and accessing the respective values in the solution vector, i.e.
>
> for (const IndexSet::ElementIterator& it=boundary_dofs.begin();
> it!=boundary_dofs.end(); ++it)
> move_boundary_values[*it] = solution(*it) +
> move_boundary_values_update[*it];
>
> This is also the approach you would need to use if you want to refine your
> mesh between time steps.
>
> All of this would of course be much simpler if your Function class would
> simply return the actual values and not just an update.
>
> Best,
> Daniel
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