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[Anders Logg <question111571@xxxxxxxxxxxxxxxxxxxxx>]

Question #111571 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/111571

    Status: Open => Answered

Anders Logg proposed the following answer:
On Wed, May 19, 2010 at 11:05:17AM -0000, Patrick Riesen wrote:
> New question #111571 on DOLFIN:
> https://answers.launchpad.net/dolfin/+question/111571
>
> hello dolfins
>
> after using mesh.move(...) in  a (time-)step, i see that the vector of dofs of a function based on that mesh still correspond to the unmoved mesh, so in a next step, i need to update the function dofs to the new mesh cells.
>
> if i use tabulate_coordinates() and tabulate_dofs() and replace the old dofs with those evaluated at the new dof coordinates i should be fine, or is there something else i have to take into account?
>
> i'm not really sure what and what not is happening in dolfin concerning functions based on the mesh which is being moved.
>
> thank you for the support,
> regards,
> patrick

I suggest taking this into account in your discretization (instead of
interpolating values to the new mesh). There is nothing in DOLFIN that
handles this automatically.

Think about your finite element basis functions as being time-dependent:

  phi_i = phi_i(x, t)

Then take that into account when you set up your space-time finite
element discretization and note that the time derivative will hit
phi_i(x, t), which gives rise to an additional term, the "ALE" term
-grad(u)*w where w is the velocity of the mesh.

--
Anders

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