Hinge boundary condition

[Мария Бронзова]

Dear colleagues, 

I was trying to prescribe displacement boundary conditions on a 3D model on certain faces but only for the x and y displacement components. I used to apply the interpolate_boundary_values class before,  but it demands dim+1 components inside my boundary_function (i have a mixed displacement-pressure formulation problem), when I call fe.component_mask(velocities). 

Could you please let me know, how I can otherwise impose my Dirichlet condition for chosen displacement components?

Thank you!

[Wolfgang Bangerth]

The function takes an argument that specifies which components of the
solution to constrain. In your case, you would provide a mask that only
specifies, for example, the x and y components. The input function is
still a dim-dimensional function, but its z component will simply be
ignored.

Best
W.


--
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Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[Мария Бронзова]

Oh, logic, thank you a lot!

среда, 3 ноября 2021 г. в 17:59:30 UTC+1, Wolfgang Bangerth:

[Wolfgang Bangerth]

On 11/3/21 12:45 PM, Мария Бронзова wrote:
> Oh, logic, thank you a lot!

Would you like to suggest edits to the documentation of that function
that would have made that point clearer? Updating parts of the
documentation often make for excellent first patches!

[Мария Бронзова]

I somehow didn't come up intuitively with the idea of taking a closer look at the fe.component_mask parameter. I believe it would be helpful to have an extension with an example in some of the tutorial steps. 

Like in step-20 or so:

Depending on the type of the prescribed Dirichlet boundary conditions the VectorTools::interpolate_boundary_values() class can be used to interpolate boundary conditions as well on single boundary degrees of freedom. The fe.component_mask inside VectorTools::interpolate_boundary_values() specifies the desired components for selection. 

For instance, we want to set only x and y displacement components on the boundary with the id=3 to a certain value, according to the BoundaryValue<dim>() function, then the VectorTools::interpolate_boundary_values() class can be modified in the following manner:

DoFTools::make_hanging_node_constraints(dof_handler, constraints);

std::vector<bool> choice={true,true,false,false};

VectorTools::interpolate_boundary_values(dof_handler,

    3,

    BoundaryValue<dim>(),

    constraints,

    fe.component_mask(choice));

With kind regards,

Mariia

среда, 3 ноября 2021 г. в 20:34:02 UTC+1, Wolfgang Bangerth: