[CIG-SHORT] Question about Dirichlet Boundary Conditions

[Matthew Knepley]

On Mon, Dec 31, 2018 at 11:20 AM tu xiang <tuxiang2016 at outlook.com> wrote:

> Hello, everyone
> I am very confused about Dirichlet Boundary Conditions.
> Such as the example given by the manual:
> [pylithapp.problem]
> bc = [mybc]
> [pylithapp.problem.bc.mybc]
> label = group A
> bc_dof = [2] ; fixed displacement in z direction
> db_initial = spatialdata.spatialdb.SimpleDB
> db_initial.iohandler.filename = disp_A.spatialdb
> db_initial.query_type = nearest ; change query type to nearest point
> algorithm
> db_rate = spatialdata.spatialdb.UniformDB
> db_rate.values = [displacement-rate-z]
> db_rate.data = [1.0e-06 * m/s] ; velocity is 1.0e-06 m/s
>
> From the manual, bc_dof = [2] (fixed displacement in z direction) means
> the displacement in z direction is fixed, but  it laterly says group A
> moves at a speed of 1.0e-06 m/s in the z direction. How could this
> happen? Group A is fixed and moves at a speed of 1.0e-06m/s  in z
> direction at the same time?
>
> Hope someone can give a detailed explanation.
>

The displacement in z is fixed on this boundary. It is is fixed to a
time-dependent value prescribed by the spatial database.
Being fixed means that it does not respond to the internal forces, but
rather is determined completely by the spatialdb.

  Thanks,

    Matt


> Best regards,
> Tu Xiang
>
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