Re: [deal.II] Applying non-homogeneous Neumann BC in step-18
On 7/15/23 11:33, Mohammad Amir Kiani Fordoei wrote: const Tensor<1,dim> n = fe_face_values.normal_vector(q_point); cell_rhs (i)+=( (n*traction_component*fe_face_values.shape_value(i, q_point))* fe_face_values.JxW(q_point)); }//for q_point }//for dof_per_cell But in computation of cell rhs i get this error: /home/amir/eclipse-workspace/mech1/mech.cc:983:22: error: no match for ‘operator+=’ (operand types are ‘double’ and ‘dealii::Tensor<1, 3>’) 983 | cell_rhs (i)+=( (n*traction_component*fe_face_values.shape_value(i, q_point))* | ^~ 984 | fe_face_values.JxW(q_point)); As error says, the normal vector with 3 component cannot be multiplied by double values in other terms. No, that's not actually what the error message says :-) It doesn't say anything about multiplication. If you read it carefully, it says that you cannot assign a right hand side of type Tensor<1,3> to a left hand side of type double. That makes sense. The types you have are because your right hand side is the product of n -- a tensor traction_component -- not sure, but probably a scalar fe_face_values.shape_value(i, q_point)) -- a scalar, see the function's documentation fe_face_values.JxW(q_point) -- a scalar What you *want* is a vector-valued shape function. You get that by "extracting" this from the fe_values object in the same way as is discussed in the vector-valued documentation module. I think something like this should work: FEValuesExtractors::Vector displacement(0); cell_rhs (i)+=( (n*traction_component*fe_face_values[displacement].shape_value(i, q_point))* fe_face_values.JxW(q_point)); Best W. -- Wolfgang Bangerth email: bange...@colostate.edu www: http://www.math.colostate.edu/~bangerth/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/9f48ee6b-cf61-499b-985e-268524743ee0%40colostate.edu.
Re: [deal.II] Applying non-homogeneous Neumann BC in step-18
Dear Wolfgang
Sorry for late response. Due to internet censorship in Iran, I didn't have
access to google group for few days.
I consider a specific region on triangulation for Neumann BC (a force
vector in 3D space).
There must be some mistakes in my program, but I couldn't figure out.
I tried to follow your instruction on:
https://groups.google.com/g/dealii/c/_4eeywhhxk4/m/myLiTWCqBgAJ .
So, I used this:
for (unsigned int i = 0; i < dofs_per_cell; ++i)
{
for (unsigned int q_point = 0; q_point < n_face_q_points ; ++q_point)
{
const Tensor<1,dim> n = fe_face_values.normal_vector(q_point);
cell_rhs (i)+=( (n*traction_component*fe_face_values.shape_value(i,
q_point))*
fe_face_values.JxW(q_point));
}//for q_point
}//for dof_per_cell
But in computation of cell rhs i get this error:
/home/amir/eclipse-workspace/mech1/mech.cc:983:22: error: no match for
‘operator+=’ (operand types are ‘double’ and ‘dealii::Tensor<1, 3>’)
983 | cell_rhs (i)+=(
(n*traction_component*fe_face_values.shape_value(i, q_point))*
|
^~
984 | fe_face_values.JxW(q_point));
As error says, the normal vector with 3 component cannot be multiplied by
double values in other terms.
Additionally, my traction component (for example in x-direction) is
preserved for dofs of other directions.
I know these mistakes, but I cannot figure out proper solution for them.
I have read steps 7, 18, 20, 21 and also reviewed lectures 21.~21.65. But I
couldn't find similar codes.
Thanks for your consideration.
Best regards
Amir
On Thursday, July 13, 2023 at 4:43:37 AM UTC+3:30 Wolfgang Bangerth wrote:
> On 7/11/23 05:32, Mohammad Amir Kiani Fordoei wrote:
> > Screenshot from 2023-07-11 14-01-30.png
> > As I understood, I just need to specify a boundary_id on triangulation
> and
> > apply traction force on that with code like this:
> > { - loop over cells
> > -loop over faces per cell && controlling being at_boundary
> > -loop over quadrature points of face
> > -loop over dof per cell && controlling intended boundary_id_NBC
> > -finally adding this term to rhs as
> > cell_rhs (i)+=
> > (fe_face_values.shape_value (i,q_point)
> >
> > *traction_component
> >
> > *fe_face_values.JxW(q_point));}
> > But, I didn't see noticble variation of displacement or norm of stress
> in my
> > solution, even for large traction force.
> > is it necessary to multiply traction_component to "* present_timestep *
> > velocity " (like Dirichlet BC displacement)? (I tried this too, but
> similar to
> > previous one no significant effect of load was observed.)
>
> Is this a boundary where you are still *also* applying a prescribed
> displacement? You can only do one or the other.
>
> Best
> W.
>
> --
>
> Wolfgang Bangerth email: bang...@colostate.edu
> www: http://www.math.colostate.edu/~bangerth/
>
>
>
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Re: [deal.II] Applying non-homogeneous Neumann BC in step-18
On 7/11/23 05:32, Mohammad Amir Kiani Fordoei wrote:
Screenshot from 2023-07-11 14-01-30.png
As I understood, I just need to specify a boundary_id on triangulation and
apply traction force on that with code like this:
{ - loop over cells
-loop over faces per cell && controlling being at_boundary
-loop over quadrature points of face
-loop over dof per cell && controlling intended boundary_id_NBC
-finally adding this term to rhs as
cell_rhs (i)+=
(fe_face_values.shape_value (i,q_point)
*traction_component
*fe_face_values.JxW(q_point));}
But, I didn't see noticble variation of displacement or norm of stress in my
solution, even for large traction force.
is it necessary to multiply traction_component to "* present_timestep *
velocity " (like Dirichlet BC displacement)? (I tried this too, but similar to
previous one no significant effect of load was observed.)
Is this a boundary where you are still *also* applying a prescribed
displacement? You can only do one or the other.
Best
W.
--
Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see
https://groups.google.com/d/forum/dealii?hl=en
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[deal.II] Applying non-homogeneous Neumann BC in step-18
Dear Deal.II group
I am trying to add boundary force (b) to step-18 as below
[image: Screenshot from 2023-07-11 14-01-30.png]
As I understood, I just need to specify a boundary_id on triangulation and
apply traction force on that with code like this:
{ - loop over cells
-loop over faces per cell && controlling being at_boundary
-loop over quadrature points of face
-loop over dof per cell && controlling intended boundary_id_NBC
-finally adding this term to rhs as
cell_rhs (i)+=
(fe_face_values.shape_value (i,q_point)
*traction_component
*fe_face_values.JxW(q_point));}
But, I didn't see noticble variation of displacement or norm of stress in
my solution, even for large traction force.
is it necessary to multiply traction_component to "* present_timestep *
velocity " (like Dirichlet BC displacement)? (I tried this too, but similar
to previous one no significant effect of load was observed.)
instead of procedure described in step-18, can I use functions "
create_right_hand_side" and "create_boundary_right_hand_side" of
VectorTools for applying body and traction force, respectively or they just
belongs to Laplace equation?
Thanks for considering this!
Amir
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