Ok, thanks Wolfgang and Daniel!
I will follow your advise and post updates on this issue.
/Erik
2016-09-30 5:54 GMT+02:00 Wolfgang Bangerth <bange...@colostate.edu>:
> On 09/28/2016 11:32 PM, Erik Svensson wrote:
>
>>
>>
>> I’m trying to implement homogeneous Neumann bc on part of the boundary in
>> tutorial example step-20.
>>
>> The Neumann bc should be imposed strongly (as for Dirichlet bc in normal,
>> non-mixed, formulation). Is this correct?
>>
>> In any case, I’m trying to impose the Neumann bc strongly using the
>> technique
>> from step-22.
>>
>> Running program I get the error:
>>
>> ---
>> An error occurred in line <1878> of file
>> </usr/local/dealii/dealii-8.4.1/include/deal.II/numerics/vec
>> tor_tools.templates.h>
>> in function
>> void
>> dealii::VectorTools::{anonymous}::do_interpolate_boundary_values(const
>> M_or_MC<DoFHandlerType:: dimension, DoFHandlerType:: space_dimension>&,
>> const
>> DoFHandlerType&, const typename dealii::FunctionMap<DoFHandlerType::
>> space_dimension>::type&, std::map<unsigned int, double>&, const
>> dealii::ComponentMask&, dealii::internal::int2type<dim_>) [with
>> DoFHandlerType
>> = dealii::DoFHandler<2>; M_or_MC = dealii::Mapping; int dim_ = 2; typename
>> dealii::FunctionMap<DoFHandlerType:: space_dimension>::type =
>> std::map<unsigned char, const dealii::Function<2, double>*,
>> std::less<unsigned
>> char>, std::allocator<std::pair<const unsigned char, const
>> dealii::Function<2,
>> double>*> > >]
>> The violated condition was:
>> cell->get_fe().is_primitive (i)
>> The name and call sequence of the exception was:
>> ExcMessage ("This function can only deal with requested boundary "
>> "values
>> that correspond to primitive (scalar) base " "elements")
>> Additional Information:
>> This function can only deal with requested boundary values that
>> correspond to
>> primitive (scalar) base elements
>> ---
>>
>> Can someone please help me to interpret the error message, or even better
>> guide me how to proceed implementing the Neumann bc?
>>
>
> Erik -- imposing zero Neumann boundary values for the mixed Laplace
> implies that the normal velocity is zero on the boundary. This is no
> problem if you discretize the velocity variable through the ordinary
> Lagrange elements, but in step-20 we use the div-conforming Raviart-Thomas
> element for which this function is not equipped to handle the situation
> because the Raviart-Thomas element mixes both the x- and y-components of
> the velocity vector.
>
> I think you should be able to use
> VectorTools::project_boundary_values_div_conforming
> instead to do what you want to do.
>
> Best
> W.
>
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: bange...@colostate.edu
> www: http://www.math.colostate.edu/~bangerth/
>
>
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