Hello Xinzeng,
You can find one use of MeshFunction in this
regression test for a libMesh based library (GRINS):
https://github.com/grinsfem/grins/blob/master/test/regression/test_turbulent_channel.C
Here, we are creating a MeshFunction (turbulent_bc_values) to map a 1-d
turbulent boundary layer solve on an extremely fine mesh, into the inlet
boundary of a 2-d channel with a coarser mesh.
The input data (data-1d) is read in from an xda file:
https://github.com/grinsfem/grins/blob/master/test/test_data/turbulent_channel_Re944_grid.xda
Thanks.
On Thu, Nov 17, 2016 at 4:28 PM, Xinzeng Feng <[email protected]>
wrote:
> Hi Roy,
>
> Thanks for your response!
>
> I think my goal is really to first assign discrete data to a FE mesh, and
> then pass it to an interface for arbitrary x,y,z points. To achieve this, I
> can pass the data to a System object and initialize it with project_vector.
> But I "guess" that MeshFunction might serve the purpose as good which, as
> you pointed out, takes data on finite element mesh and gives an interface
> for data at x,y,z points. But I have no idea how MeshFunction is
> initialized given discrete data.
>
> Do we have member functions similar to project_solution or project_vector
> work for MeshFunction?
>
> Xinzeng
>
> On Thu, Nov 17, 2016 at 10:06 AM, Roy Stogner <[email protected]>
> wrote:
>
> >
> > On Wed, 16 Nov 2016, Xinzeng Feng wrote:
> >
> > I'm a new user of libMesh. I am trying to incorporate patient-specific
> MRI
> >> data with a finite element model. For this purpose, I want to define a
> >> field map with nodal values assigned based on the images. The field then
> >> needs to be integrated to assemble the stiffness matrix.
> >>
> >> I've noticed that the MeshFunction class provides function-like objects
> >> for
> >> data distributed over a mesh, which might serve the need. But I'm not
> sure
> >> how to correctly use it.
> >>
> >
> > I think MeshFunction is actually the converse of what you want.
> > MeshFunction takes data on a finite element mesh and gives you an
> > interface for data at x,y,z points. You want to take data defined at
> > x,y,z points and assign it to finite element degrees of freedom on a
> > mesh.
> >
> > For that latter problem, what you'll want to do is define your own
> > function subclass, then pass it to System::project_solution() or
> > System::project_vector(). We do this in several of the example codes;
> > transient_ex1 (where we project initial conditions from an exact_value
> > function pointer) might be the clearest.
> > ---
> > Roy
> >
>
>
>
> --
> Xinzeng Feng, Ph.D.
> Institute for Computational Engineering and Sciences, Postdoctoral Fellow
> University of Texas, Austin
> ------------------------------------------------------------
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>
--
Vikram Garg
Postdoctoral Associate
The University of Texas at Austin
http://vikramvgarg.wordpress.com/
http://www.runforindia.org/runners/vikramg
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