Hello,

On Thu, May 23, 2019 at 3:45 PM Nikrouz <nikrouz....@gmail.com> wrote:

> Dear All libMesh uses,
>
> I want to apply traction boundary condition on two of the surfaces of my
> geometry. As far as I know, There are two methods
>
> for defining such a boundary condition: *Using penalty method*


The penalty method is used for enforcing Dirichlet boundary conditions.


> and
> *side_time_derivative method*.


This is correct, but it is used within the FEMSystem framework. You'd want
to refer to the fem_system examples in this case.


> I have a couple of questions:
>
>
> 1- Which method is more straightforward for defining boundary
> condition(traction) in libMesh?
>

Please have a look at the following example:
https://github.com/libMesh/libmesh/blob/master/examples/systems_of_equations/systems_of_equations_ex6/systems_of_equations_ex6.C

It is a "plain" (non FEMSystem) example. If you look in the assemble()
function, you will see that following the element interior loop, there is a
loop over boundary elements and then the traction is applied appropriately.

HTH,

Paul


> 2- I have searched different examples in libMesh and I could not find
> any case that has used side_time_derivative method(for example defined
> in fem-ex3). Is there any example illustrates how can I call the
> mentioned method in the code? Where should I call it?How?
>
> In the example fem3 example, the method need two inputs:
>
> *bool ElasticitySystem::side_time_derivative (bool request_jacobian,**
> **                                             DiffContext & context)*
>
> *FEMContext & c = cast_ref<FEMContext &>(context);
>
>    // If we're on the correct side, apply the traction
>    if (c.has_side_boundary_id(BOUNDARY_ID_MAX_X))
>      {
> *
>
> *......*
>
>
> How and where should I use this method in the code to have a traction
> boundary condition?
>
> Thank you everybody!
>
>
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