ok, I added this possibility.
Yves
On 11/11/2020 14:15, Andriy Andreykiv wrote:
Dear Yves,
I agree, that would be the simplest solution.
Best regards,
Andriy
On Wed, 11 Nov 2020 at 13:59, Yves Renard <[email protected]
<mailto:[email protected]>> wrote:
Dear Jean-François and Andriy,
The simplest way for the import in python of gmsh files with the
activated option for the lower dimension elements is to define it
as a new format, may be something as "gmsh_with_lower_dim_elt". I
can add it, this is very simple to do.
Best regards,
Yves
On 11/11/2020 13:30, Andriy Andreykiv wrote:
Jean-François,
Yes, I use a classical region to store the elements. A region
with line elements is not different from any other region.
Regarding the numerical difficulties you're referring to, well,
we didn't have singularities there.
We also had a Neuman like term (mixed Dirichlet/Neuman condition
that was switching depending on the solution, geomechanical
sink), but no issues like yours.
You might consider consulting Yves Renard
<mailto:[email protected]> about it. Maybe you can also
use special shape functions in the 3D elements around your lines.
For example, I know Getfem supportsX-Fem
<http://getfem.org/userdoc/xfem.html#xfem> and maybe you could
enrich your solution with some asymptotic shape functions around
the line elements.
Best regards,
Andriy
On Tue, 10 Nov 2020 at 23:39, Jean-François Barthélémy
<[email protected]
<mailto:[email protected]>> wrote:
Thank you very much Andriy. This is clear. It seems that the
problem relies on the current limitation of import and not on
the assembly implementation. However the documentation made
me think that a region in a mesh of dimension N could only
store elements of dimension N or faces of dimension N-1 bit
not less and as the bricks require a region ID I was afraid
that it would be a limitation although of course there is no
fundamental problem in integrating lineic terms... In your
problem, you also use a classical region ID to store your
line terms, don't you?
Well other issues may arise from this kind of term defined on
a line: indeed the solution induced by a Neumann lineic term
is expected to take infinite values in the vicinity of the
line (think about Green function in a conductive or elastic
problem which varies as ln(r) close to the line or 1/r for a
pointwise Neumann term). Then a linear or nonlinear term
involving the local solution at the line itself and
contributing to the matrix term (lhs) may cause problem or at
least lead to an unreliable solution. Have you encountered
such difficulties?
Best regards
Jean-François
-------- Message d'origine --------
De : Andriy Andreykiv <[email protected]
<mailto:[email protected]>>
Date : 10/11/2020 22:10 (GMT+01:00)
À : Jean-François Barthélémy <[email protected]
<mailto:[email protected]>>
Objet : Re: Terms on a physical line in 3D
Dear Jean-François,
Unfortunately I don't work in Python interface, so I don't
know. But yes, that's add_all_element_type flag.
Alternatively, if your line mesh is very simple you could add
these elements one by one to the volume mesh, in your Python
code.
Yes yes, I'm quite sure the line elements will work in high
level generic assembly. That's a generic Getfem behaviour.
We're using Getfem in our company and we have boundary
conditions,
defined on line elements, embedded in a volumetric mesh. We
define non-linear terms using high-level assembly on those
line elements.
I suspect it's me or my colleague Liang Jin who actually
introduced this flag, so that we can import these line
elements, because the previous behaviour was
that these line elements were always skipped.
So, yes, if you are able to recompile getfem and the
interface that would be the simplest solution. You might
choose to commit your changes to Getfem repo as well.
Best regards,
Andriy
On Tue, 10 Nov 2020 at 19:13, Jean-François Barthélémy
<[email protected]
<mailto:[email protected]>> wrote:
Dear Andriy,
Thank you for your answer.
Is the flag that you mention the boolean
"add_all_element_type" which is set to false by default
in getfem_import.cc?
I should have mentioned that I was working with the
python interface and it seems that this flag cannot be
changed from the python interface. The current behavior
is that a GMSH physical line is imported as the surface
region containing convexes which have an intersection
with the line, which is of course not what I need.
Anyway, do you suggest that I recompile getfem and the
python API by setting a default true value for this flag
in order to get the physical lines properly stored in a
region? Afterwards you are sure that a "line" region
would work in the high level generic assembly? If this is
the case, I wonder why the developers have set this flag
to the default false value, do you know why?
Thank you very much
Best regards
Jean-François
Le mar. 10 nov. 2020 à 16:57, Andriy Andreykiv
<[email protected]
<mailto:[email protected]>> a écrit :
Dear Jean-François,
Yes, this is possible. It was routinely done before.
You need to have your 3D mesh AND line elements
explicitly defined (Getfem doesn't have edges of
volume elements as entities).
You could use GMSH for that or define the mesh in
your code. In GMSH you can assign physical domains to
all elements, including your line elements.
During the import of your GMSH mesh you would need to
set somewhere a flag "not to ignore lower dimension
elements", so that your lines are getting properly
imported.
After importing GMSH mesh into getfem::mesh and
having region ID's for the volume as well as for the
line elements you can define their interpolations
(getfem::mesh_fem),
integration methods (getfem::mesh_im), create a
getfem::model, add unknown variables and use higher
order assembly to define your nonlinear terms.
Best regards,
Andriy
On Tue, 10 Nov 2020 at 16:29, Jean-François
Barthélémy <[email protected]
<mailto:[email protected]>> wrote:
Dear Getfem users,
I have a 3D mesh in which physical lines are
identified (ie set of edges). These lines may be
on the boundary or in the interior of the domain.
I would like to build a model incorporating
(linear and even nonlinear) terms on these lines
(ie integration domain of dimension m.dim()-2).
This could be used for example to model a
concentrated line of current injection in an
electric ohmic problem (rhs term) or a lineic
domain of high conductivity (contributing then to
the matrix term). Is there any way to do so in
Getfem?
Thank you in advance
Best regards
Jean-François Barthélémy
--
Yves Renard ([email protected]
<mailto:[email protected]>) tel : (33) 04.72.43.87.08
INSA-Lyon
20, rue Albert Einstein
69621 Villeurbanne Cedex, FRANCE
http://math.univ-lyon1.fr/~renard
---------
--
Yves Renard ([email protected]) tel : (33) 04.72.43.87.08
INSA-Lyon
20, rue Albert Einstein
69621 Villeurbanne Cedex, FRANCE
http://math.univ-lyon1.fr/~renard
---------
