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:yves.ren...@insa-lyon.fr> 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
<jfrancois.barthel...@gmail.com
<mailto:jfrancois.barthel...@gmail.com>> 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 <andriy.andrey...@gmail.com
<mailto:andriy.andrey...@gmail.com>>
Date : 10/11/2020 22:10 (GMT+01:00)
À : Jean-François Barthélémy <jfrancois.barthel...@gmail.com
<mailto:jfrancois.barthel...@gmail.com>>
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
<jfrancois.barthel...@gmail.com
<mailto:jfrancois.barthel...@gmail.com>> 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
<andriy.andrey...@gmail.com
<mailto:andriy.andrey...@gmail.com>> 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
<jfrancois.barthel...@gmail.com
<mailto:jfrancois.barthel...@gmail.com>> 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 (yves.ren...@insa-lyon.fr) tel : (33) 04.72.43.87.08
INSA-Lyon
20, rue Albert Einstein
69621 Villeurbanne Cedex, FRANCE
http://math.univ-lyon1.fr/~renard
---------
