Thanks very much, Jean-Paul,
during the time i was waiting for the answer, i kind of figured out a way
similar to the first one,
now since you have also proposed a more elegant way, i will look into it
also. Thanks,
best,
lailai
On Wednesday, January 16, 2019 at 12:08:18 PM UTC-5, Jean-Paul Pelteret
wrote:
>
> Dear Laila,
>
> I have two suggestions that may help you here:
>
> 1/ You could add the boundary ID as an argument to
> the PoiseuilleBoundaryValues class:
>
> template <int dim>
> class PoiseuilleBoundaryValues : public Function<dim>
> {
> public:
> PoiseuilleBoundaryValues (const typename types::boundary_id b_id)
> : Function<dim>(dim+1),
> b_id (b_id)
> {}
>
> …
>
> private:
> const typename types::boundary_id b_id;
> };
>
> If you do so then you could return a different value based on the boundary
> ID for which the specific instance of this class.
>
> template <int dim>
> double
> PoiseuilleBoundaryValues<dim>::value (const Point<dim> &p,
> const unsigned int component) const
> {
> Assert (component < this->n_components,
> ExcIndexRange (component, 0, this->n_components));
>
> double umax = 1.5;
>
> if (component == 0)
> {
> if (b_id == 1)
> return
> umax*(1-pow(2*p[1]/(UserGeometry::y_bottom-UserGeometry::y_top),2));
> else if (b_id == 2)
> return … etc…
> }
>
> return 0;
> }
>
> You could then make a loop over all relevant Dirichlet boundaries and
> create a specialised instance of this class and pass it to the deal.II
> function that interpolates the boundary values.
>
> for (auto b_id : {list_of_dirichlet_boundary_ids})
> VectorTools::interpolate_boundary_values (dof_handler, b_id,
> PoiseuilleBoundaryValues<dim>(b_id),…);
>
> 2/ The above is, in my opinion, not particularly elegant. The second (and
> maybe more concise and robust) option would be to use the FunctionParser
> <https://dealii.org/developer/doxygen/deal.II/classFunctionParser.html>
> class,
> which seems to be able to do everything that you are doing in
> this PoiseuilleBoundaryValues class and more. You could even write the
> evaluated expressions for each boundary within an instance of a
> ParameterHandler, so they need not be hard-coded.
>
> I hope that this helps you.
>
> Best,
> Jean-Paul
>
> On 16 Jan 2019, at 06:29, Lailai Zhu <[email protected] <javascript:>>
> wrote:
>
> hi, Dear Deal.II users,
>
> I am using deal.II to solve for a simple flow with multiple inlets
> where I need to impose Pouseuille BC (dirichlet) with different
> magnitudes.
> I used to use the following piece of code together with
> VectorTools::interpolate_boundary_values
> to work for one BC. This is rather hard-coded, where I know the maximum
> velocity of this the BC, the locations of the BC, which is ok for only one.
>
> Now the issue arises if i have around 10 inlets to impose, these inlets
> can in general have different positions, velocity magnitudes and channel
> widths. I can also duplicate the following codes 10 times and customize
> each corresponding to each inlet. However, this does not sound so elegant,
> may I ask whether there might be some smarter way to achieve this?
>
> Thanks in advance,
>
> best,
>
> lailai
>
>
> template <int dim>
> class PoiseuilleBoundaryValues : public Function<dim>
> {
> public:
> PoiseuilleBoundaryValues () : Function<dim>(dim+1) {}
>
> virtual double value (const Point<dim> &p,
> const unsigned int component = 0) const;
>
> virtual void vector_value (const Point<dim> &p,
> Vector<double> &value) const;
> };
>
>
> template <int dim>
> double
> PoiseuilleBoundaryValues<dim>::value (const Point<dim> &p,
> const unsigned int component) const
> {
> Assert (component < this->n_components,
> ExcIndexRange (component, 0, this->n_components));
>
> double umax = 1.5;
>
> if (component == 0)
> return
> umax*(1-pow(2*p[1]/(UserGeometry::y_bottom-UserGeometry::y_top),2));
>
> return 0;
> }
>
>
> template <int dim>
> void
> PoiseuilleBoundaryValues<dim>::vector_value (const Point<dim> &p,
> Vector<double> &values) const
> {
> for (unsigned int c=0; c<this->n_components; ++c)
> values(c) = PoiseuilleBoundaryValues<dim>::value (p, c);
> }
>
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