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]> 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 <[email protected]>
> about it. Maybe you can also use special shape functions in the 3D elements
> around your lines.
> For example, I know Getfem supports X-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]> 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]>
>> Date : 10/11/2020 22:10 (GMT+01:00)
>> À : Jean-François Barthélémy <[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]> 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]> 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]> 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]) tel : (33) 04.72.43.87.08
> INSA-Lyon
> 20, rue Albert Einstein
> 69621 Villeurbanne Cedex, FRANCE
> http://math.univ-lyon1.fr/~renard
>
> ---------
>
>
